Meet the Crimson Rambler

When I was a child, my mother...like many other mothers...used to say, "Good night.  Sleep tight. Don't let the bed bugs bite!".  Good advice for a child not sure what bed bugs really were...otherwise I'd probably have had nightmares!  I spent most of my young life thinking bed bugs were mythical because of that phrase.  As I got older, I discovered that they were very real creatures that actually do bite people as they sleep.  As you can imagine, I was filled with fear and panic when I first learned about how pesky these little buggers can be.  As I've grown into the young parasitologist that I am, these pests have moved from something I fear to something I find fascinating.  Like most other parasites, these guys have very interesting lives and guess what...they aren't terribly dangerous to tell the truth.  The worst they can do is be an annoyance and an extremely difficult one to rid yourself of at that.  So, today we look at the strange lives of these odd insects that have had aliases such as the "wall louse", "heavy dragon", "chinche bug", "redcoat", and my personal favorite, "crimson rambler".  

Taxonomy
These animals belong to the largest of all the animal phyla: Phylum Arthropoda.  Within this phylum they exist as members of class Insecta.  Something tells me you can guess what other types of creatures make up this class.  They belong to order Hemiptera, meaning "half-wing", which refers to the partially membranous wings of most member of this order.  Interestingly enough, not all members of this order have wings (as we see with bed bugs).  However, members of this order do all possess piercing-sucking mouthparts often called the proboscis. This is used for penetrating tissues..both animal and plant in nature. They further belong to family Cimicidae.  Members of this family are all wingless blood-feeders that seek out birds, bats, and humans. There are 22 genera within this family; twelve feed on bats, two on humans, and the rest on birds...typically birds that live in caves or along cliffs.  The three species that feed on humans are colloquially called "bed bugs" due to their nocturnal feeding habits.  These three are Cimex lectularius, Cimex hemipterus, and Leptocimex boueti. The first is the most commonly found species globally, but prefers temperate climates, while the second prefers more tropical areas.  The last is found only in West Africa.

Bed Bug Bodies

SEM of a bed bug.  The piercing mouthparts have
been artificially colored with purple and red.

As mentioned previously, these little bugs are wingless...actually, if you want to be technical, they have vestigial (reduced to the point of being useless) wings. As adults, they are small reddish-brown ovals reaching as big as 5mm x 3mm in size.  Newly hatched nymphs are transparent, but become progressively darker as they go through successive molts.  These insects use chemical signals to communicate with one another about nesting, feeding, and reproducing.

Coming Out of the Woodwork...Err...Cave-work?!
These insects can proliferate quickly and be extremely difficult to eradicate once they have an established home.  But where did they originally come from?  Though no one can say for sure when or where bed bugs originated, we do know that the three species that feed on humans are also known to feed on bats.  It is likely that humans picked up these parasites from living in caves alongside infested bat colonies.  C. lectularius has also been known to feed on rodents, which may have helped to spread these insects into human dwellings outside of caves.

There is a long and fascinating history associated with these little bugs, but I'll save that for a future post. Today, we are experiencing a time of resurgence in bed bug populations.  As more people take over the planet, we build more places to house more people in fewer areas.  This space-saving comes with a price. Not only are apartments, dorms, and condos more prone to infestations with cockroaches and ants, now we are seeing more and more cases of bed bug infestations as well.  As you probably would have guessed, they are a bigger problem in places with larger populations.

The Feeding: Adventures of the Crimson Rambler
After closing your eyes and drifting off to dreamland, these little creatures make their way out of mattresses, dressers, pillows, and cracks or crevices in the walls near your bed. They find their way to you by detecting the carbon dioxide you exhale with every breath, by feeling the warmth of your body heat as they get closer, and by using a variety of navigation chemicals.

After discovering your exposed skin, the creatures pierce you with their tiny little beaks.  This blood derrick finally strikes paydirt when it enters into a blood vessel.  From here, the pressure within the vessel itself forces this iron-rich liquid into the body of this miniscule beast. Their bites are not painful and often go unnoticed in the beginning. The wounds left behind eventually become small itchy welts around your neck, arms, and jaw. The bug draws on the fresh blood for the next 5-10 minutes before dropping off and crawling back into the home from which they emerged. This is a ritual that occurs every 5-10 days.

Despite the fact that these creatures tend to feed once or twice a week, they can actually go for about 5 months without feeding under typical conditions.  Under ideal conditions (for them) they can live for up to a year.  Speaking of time, here's a fun fact: These insects digest their blood meals slowly and human DNA can be recovered from bed bugs up to 90 days post feeding!  This gives them a unique place in forensic entomology for determining whether or not a person was in a place where the bed bugs were found!

Male (behind) traumatically inseminating a female.

And the Most Traumatizing Mating Ritual Goes To...
One of the things that I've always found most fascinating about bed bugs is their means of reproduction.  These animals mate when a male finds a female, grabs her from behind, and literally stabs her in the abdomen with his hypodermic genitalia.  That's right hypodermic genitals.  After the stabbing, he ejaculates into her body and the sperm swim around in her hemolymph until they reach sperm storage structures.  Eventually, the sperm are released and move to the ovaries where fertilization occurs.  This process is appropriately called traumatic insemination.

Human Health Issues

Bed bug welts.

Despite being exclusive blood feeders, and being known to become infected with over 28 human pathogens, these animals have never been documented to have transmitted any diseases to humans.  The worst that these bugs can do is cause skin irritation that may be mild or could cause blisters in sensitive individuals. The biggest problem humans experience when living with bed bugs is the psychological effect associated with living in an infested home.  Much fear and disgust surrounds these organisms, and it is easy to have such feelings when faced with an infestation. 

These bugs are often associated with sub-par living spaces in our minds, but the truth is that a home can be a very nice home and still get an infestation.  They can be brought into a home through clothing, luggage, furniture, etc. from an infested home.  They can also come from wild animals or pets that have been exposed to nesting sites.

Detection and Management
Bed bugs are not always easy to detect because they are nocturnal feeders, usually feeding in the wee hours of the morning.  If you haven't had any reactions to the bites, you can still detect bed bugs by finding their fecal spots, blood smears on your bedding, or empty exoskeletons left behind as the insects molt.

A bed bug harborage.

Sometimes you can find a single bed bug, but they are more often found congregated at nesting sites.  These clusters of bed bugs, young and old, are often known as "harborages" and are the end of the chemical trail after feeding for most of these insects.  Harborages can exist in bedding, luggage, furniture...even electrical sockets and laptops.

Some people employ the help of specially trained bed bug detection dogs to help them find harborages.  Apparently, these dogs are very good at their jobs.  Under controlled lab conditions, these dogs are 97.5% accurate.  Of course, we expect that rate to be lower under real-world conditions, but that's still pretty impressive! Bed bugs are said to have a smell that some describe as rotting raspberries.  Trained dogs can typically pick up on the origins of these smells within minutes, which pest control specialists usually need about an hour.

A New York bed bug detection dog.

Bed bugs die if exposed to 115°F heat for 7 minutes or more.  Heat along with pesticides like malathion are the best course of action for managing bed bug infestations.  These animals can also be killed by freezing temperatures, but this takes several days rather than a matter of minutes. It is also recommended to vacuum areas, heat treat bedding and mattresses, and above all else to call in professionals to help with eradication efforts.  In extreme cases, you may have to dispose of a heavily infested mattress or couch.


There was an interesting paper that came out recently talking about a traditional method of bed bug control that involved the use of plant leaves scattered around the bed as traps.  Apparently this method actually works to some degree and scientists are working to develop artificial traps that have the same design as the hairs on these bed bug-snaring leaves.  More about that paper in a future post.

Bed bugs and their eggs
inside an infested dresser drawer.

To prevent bites, try to minimize the amount of skin you leave exposed while you sleep and think about infesting in a pesticide-impregnated mosquito net until you know you have gotten rid of these insects.  To prevent bringing these guys home be careful of secondhand items and sketchy hotels. Keep your luggage off the floor when possible in hotels, even non-sketchy ones may be infested. Bed bugs don't need a dirty place to live...they just need a place with hosts and lots of hiding places. Also, be sure to thoroughly look at your personal items after a trip...especially if you were in close proximity with birds or bats...and be sure to wash your trip clothing with hot water and dry them in a dryer for at least 20 minutes at a medium-high heat.

If you do develop skin problems from bites, you can treat them using a hydrocortisone cream or an oral antihistamine like Benedryl.  The bites usually heal within a few weeks.

Moral of the Story
If you get bed bugs, be sad that you have something hard to get rid of, but happy that you have something that can't transmit any sort of deadly disease! (Always a silver lining!) These creatures are fascinating even though they cause a lot of human annoyance and can be costly to eradicate from your home. Be in awe of the crimson ramblers...just hope you never have to deal with them up-close and personal! :p

Avian Trichomoniasis: A Disease that is for the Birds

Last night I got home from the 46th annual Southwestern Association of Parasitologists' meeting.  I spent Thursday night, all day Friday, and Saturday morning immersed in conversations about parasitism among other exciting topics.  My little notebook is clutter with little thoughts that popped up during the numerous and exciting presentations given by everyone from undergraduates through tenured professors.  When I sat down to create a post for today, I had a hard time deciding which topic to pick!  Then I remembered that I will be able to post on everything I learned in good time. One thing that was barely touched upon sparked my interest.  Rather than posting about something I learned a lot about (you know, the logical thing to do) I decided to post about something I had to do a little research about.  This wasn't the first time I've ever encountered Trichomonas gallinae, in fact, I mentioned it once in a blog about dinosaur parasites.  But I've never written anything else about it, and I would like to change that. So, here it is, a blog post about something that was barely mentioned and scarcely discussed at a meeting full of parasitophiliacs, just because I can.

Trichomonas gallinae is not a human parasite.  This parasite instead infects a variety of birds.  It is most often found in columbids (doves and pigeons) but has also been known to infect chickens (no wonder with an epithet like "gallinae"...the scientific name for a chicken is Gallus gallus), turkeys (which are in the same order as chickens...the order galliformes), and a variety of raptors (birds of prey like hawks and eagles).  As late as 2005, reports of the disease were coming out about new bird host species.  The disease is widespread and, as you may have already guessed, very much not host-specific.  But before we go any further, let us look at this protist's taxonomic status.

Taxonomy
 Like all protists, this organism is a eukaryote, separate from bacteria and archaea by the presence of true, membrane-bound organelles.  There are many debates about upper taxonomy, so to avoid doling out information that is not up to date, let us skip to the class level.  This organism is placed within class Parabasalia, which is thought to be one of the oldest classes of protozoans. These primitive, unicellular organisms lack mitochondria and function anaerobically.  Parabasalids are characterized by the presence of one or more clusters of flagella emerging from the anterior end of the cell.  They are named for the parabasal fibers that run between basal bodies and Golgi complexes within the cell  There are 10 orders within this class, most of which are known to live within the guts of insects (both as parasites and as symbiotic mutualists). They are further placed within the order Trichomonadida based on their morphological characters.  Member of this order usually have 4-6 flagella with one being "recurrent", meaning that one runs the length of the cell and presents much like an undulating membrane.  Those within this group that are parasites (and not all of them are) never form a cyst stage.  Instead they remain in mobile feeding stages known as "trophozoites".  Because they do not usually form a cyst stage, the major means of transmission is via direct contact. This protist belongs in the family Trichomonadidae under the type genus Trichomonas.  Members of this genus exclusively parasitize vertebrates, but non-parasitic members can be found as endosymbionts within the guts of termites. One member of this genus, T. vaginalis, parasitizes humans and is spread through sexual contact.

Life Cycle
Trichomonas gallinae has a relatively simple life cycle compared to say, most parasitic helminths.  But that doesn't make it uninteresting.  These parasites are typically found at the anterior ends of the digestive and respiratory tracts of birds or in the oral-nasal cavity of such animals.  These organisms are able to reproduce quickly via binary fission while inside a suitable host.  Again, these organisms do not form cysts, so they often die rather soon after expulsion from a host.  They move from one host to another in one of three ways:

1) As a parent bird regurgitates food or crop milk (a secretion produced by pigeons, doves, flamingos, and some penguins that includes partial sloughs of the lining from the crop and contains a great deal of protein, fats, anti-oxidants, and immune supplements including antibodies and digestive bacteria) to feed their young, the parasite can get picked up as the food passes through the upper digestive tract and/or oral cavity and transferred to the young upon ingestion. This is the main source of transmission among doves and pigeons, which could be why the parasite is so prevalent in these types of birds.  Adult birds may carry the disease asymptomatically for years...spreading the disease to their offspring long before manifesting clinical signs of infection.

2) Trophozoites can survive for a short time in water, where an uninfected host may pick up the parasite through drinking. This means of transmission is highly problematic for domesticated chickens and turkeys that drink from water or ingest food that may be contaminated with feces, saliva, or a variety of secretions coming from the crop.  Wild birds have been known as sources of infection among domestic birds, but domestic birds keep the transmission cycle going within their own flocks through this form of transmission.

3) An uninfected bird may eat an infected bird and acquire the infection in this manner. This is an especially common means of infection for birds of prey, for reasons I'm sure you can imagine.

Avian Trichomoniasis
This disease is typically found in young birds and can be found in a wide variety of virulence patterns.  Adult birds that have been infected and have recovered carry the parasite, but become resistant to reinfection.  Because of the dynamic virulence of these parasites, the rates of birds infected are not closely linked to mortality rates.  Sometimes infections are mild or even asymptomatic for years.  Other times, the disease can result in death a mere 4-18 days after infection.

The disease presents as lesions within the mouth cavity that appear white or light yellow.  The lesions result in mucosal inflammation and ulcerations that expand into the esophagus, proventriculus, and crop.  As the disease progresses, the lesions create masses of dead (necrotic) tissue that may block the passage of food and/or air.  This may cause so much pain that the birds no longer wants to eat and suffers from subsequent starvation, or it may cause emaciation or asphyxiation as the esophagus and trachea become obstructed.  In rare instances, other organs such as the liver, or the eyes can become infected and will manifest such lesions to cause organ failure.


Diagnosis, Treatment, and Prevention
Avian trichomoniasis may be diagnosed based on clinical signs such as difficulty swallowing, inflamed mucosa, and excessive salivation or by direct observation of characteristic lesions/nodules within the mouth.  The only way to confirm infection is to demonstrate the organisms microscopically from samples of fluids, nodules, or lesions.


The most efficient treatment is the administration of antiprotozoal drugs like dimetridazole or metronidazole.  Birds typically recover in as little as 1-2 days after administering such drugs.  Sometimes, oral plaques have to be removed manually using forceps before drug administration.

For domesticated birds, the best form of prevention is regular cleanings of feeders and water sources.  It is also important to try to reduce contact with wild birds that may transmit the disease or at the very least protect food and water sources from wild birds.

The spread among wild birds can be reduced by regularly cleaning wild bird feeders and bird baths, allowing adequate drying time for both before refilling them with food or water. These parasites have never been known to infect humans, but in the interest of safety from other type of avian zoonoses, it's a good idea to wear gloves when completing such chores.

Moral of the Story
First of all, writing this post taught me that just because something is grazed over at a meeting of people who love parasites doesn't make it any less significant or interesting than any other parasite. From doing the actual research itself, it is important to know about such things if you ever plan to raise domestic birds as pets or sources of meat/eggs/feathers.  It is equally important to know these things if you are a wild bird enthusiast with a backyard of bird feeders and stone baths for inviting your winged friends to join you for a mint julep on a nice, sunny afternoon.  So, keep your bird-areas clean as best you can and hope for mild cases for the birds beyond your treatment/prevention capabilities.

Long Live the Broad Fish Tapeworm! All About Diphyllobothrium latum

You may or may not be aware that eating certain foods puts you at risk of picking up parasites such as Diphyllobothrium latum.  Don't worry, I'm not going to try to talk you out of eating sushi or ceviche...I would never do that because I am a lover of both! However, it is good to be aware of the dangers of such foods so that you know what you are getting yourself into...especially in places other than the states where regulations are...less stringent, to put it mildly.  The bad news is that this parasite can go undetected for many years, and may get to be about 30 feet long in humans.  The good news is that once you've been diagnosed, our old friend Praziquantel can knock out in infection rather quickly.  So sit back, and enjoy learning about this fascinating fish tapeworm!



So what is this parasite you speak of?

Sushi from a restaurant in Chicago...I ate most of this!

Diphyllobothrium latum is commonly known as the "broad fish tapeworm".  As this common name implies, it is contracted from eating raw or undercooked fish and has a broad morphology, which we will mention again a little later. The worm is native to Scandinavia, western Russia, and the Baltics, but has been spread to North America through fish importation.  It has been historically more problematic in the Pacific Northwest than anywhere else on this continent.  As Americans expand their culinary pallets to include foods with raw or undercooked fish as the main ingredient, the risk for cases of parasite infections have increased.  Cases of infection have been reported from a variety of foods from many origins.  Sushi/Sashimi are among the biggest Asian threat.  Italian carpaccio di persico and French tartare maison make up some of the European threats. In Latin American cuisine, ceviche is a candidate for transmission as well. Luckily, food standards have become more restrictive in terms of fish importation and storage in this country.  It is not likely that you will contract this parasite here in the US, but if by some chance you do, remember that it's easy to get rid of as long as you can confirm the infection.

Carpaccio di Persico

Ceviche

Taxonomy
Like all tapeworms, this animals belongs to phylum platyhelminthes under class Cestoda.  It further belongs to order Pseudophyllida because the adults of this species possess two bothria (structures that help them attach to the host's intestinal walls) and dumbbell-shaped ovaries.  These worms also have both the genital pore and the uterine pore located in the center of their ventral (belly) sides.  D. latum belongs in family Diphyllobothriidae, which infect copepods, then later infect fish (usually), and wind up in mammals, where they grow to maturity and reproduce.  D. latum is the longest tapeworm species that infects humans, averaging 10 meters (30 feet) in length.  These worms may shed as many as one million eggs in a day.  The proglottids (segments in which eggs are produced...among other functions) of this worm are more broad than other tapeworm proglottids, hence the common name.

Scolex showing bothria on left. Proglottids on right.

Life Cycle
The life cycle of this tapeworm starts with an infected mammal shedding proglottids (laden with eggs) in their feces.  These proglottids get ingested by a copepod (this takes place in water) and the eggs develop into a procercoid larva. A small fish, such as a minnow, then eats the infected copepod and the parasite develops into a plerocercoid larva or "sparganum" within the fish's muscles.  Along comes a bigger fish that eats the smaller fish, and now the parasite can make a comfy home in the muscles of something like a trout or perch.  An unsuspecting human then eats the fish without properly cooking it to rid it of the parasites within, and now our human is infected.  Once inside the human, the parasites become immature adults and eventually develop into sexually mature adults.  They begin to reproduce, releasing their eggs in the human's feces and the cycle begins again.  These worms are restricted to humans, in fact many other animals have been reported to have harbored these worms.  There are papers describing this worm from dogs, cats, bears, weasels, and even pinnipeds (such as seals and sea lions)! Once established in a mammal host, this worm can live for up to 20 years, sometimes going completely unnoticed!

Diphyllobothriasis
The disease associated with being infected with D. latum has a long history with coastal cultures that have traditionally created foods using raw or undercooked fish.  Archaeological sites in South America have revealed eggs in 4,000-10,000 year old human remains. During the 1970s, there were over 5 million cases of diphyllobothriasis reported in Europe and over 4 million cases reported in Asia.  Symptoms of this disease are often asymptomatic (having no clinical signs or symptoms), in fact, 4 out of every 5 people who contract this worm show no signs of infection.  The remaining 1 in 5 infected persons experiences vomiting, diarrhea, and weight loss in addition to fatigue, abdominal pain, general discomfort, and constipation.  In prolonged cases, patients rarely suffer from severe vitamin B-12 deficiency as this parasite may absorb as much as 80% of B-12 within a person's body.  This deficiency can lead to megaloblastic anemia, which leads to demyelination (loss of the insulation around your nerves).  Demyelination leads to degeneration of the spinal cord
and may leave people with a variety of disfunctional nerve-related symptoms.

Diagnosis and Treatment

D. latum egg under a microscope.

Due to there often being a lack of clinical symptoms, many times this disease goes undiagnosed or gets diagnosed long after infection.  There are really only two ways to diagnose this disease.  The first way is to identify proglottids or eggs from a patient's stool sample.  The second way is to perform a PCR test following sonication to remove the eggs from the proglottids.  Sometimes, these worms can be found during a routine colonoscopy. Click here to see a video of this worm shot during a colonoscopy. Once diagnosed, the treatment plan is rather easy to administer.  Typically, a patient is given praziquantel.  This drug has some side effects that are similar to those that 1/5 patients experience from the infection itself.  Patients may also be treated with niclosamide, which has no side effects because it doesn't get absorbed by the gastrointestinal tract.

Prevention
One way to prevent the spread of diphyllobothriasis is to raise public awareness of water contamination and to encourage them not to defecate in sources of drinking water. One should always avoid eating any fish that looks questionable.  The best way to prevent the spread of this disease is to educate food handlers about how to properly prepare fish.  Fish should either be cooked thoroughly or brined before serving.  If a dish requires raw fish, the fish should be frozen at -10 degrees C for 2-3 days before being thawed and used.

Gefilte Fish

Moral of the Story
If you are planning to eat sushi or gefilte fish, be sure the fish have been prepared properly to kill off any little passengers that may have been hanging out in the fish muscles.  If you think you may have accidentally ingested a fish tapeworm, see a doctor so that you don't carry around your new friend for a few decades.  Also, don't be mad at D. latum, remember, he/she is just trying to survive!  And by the way, sushi is still delicious, so the risk of getting an easily treatable tapeworm infection is certainly not going to keep me from enjoying it! :P

See? We LOVE sushi!!! :p

Here's a close-up of the sushi bridge we ordered! :)

A Love Letter About My First Parasite Encounter: Meet Ascaris lumbricoides

Okay, so this person has green gloves, but the purple
are much more memorable to me!

The name Ascaris lumbricoides holds special significance for me. This enormous nematode was the first parasite I ever learned about in any great detail.  I can remember sitting there in the Zoology lab on the second floor of Bolin Science Hall and staring at this odd preserved creature resting harmlessly in the dissection tray before me.  We had all been warned that the eggs from these animals could sometimes survive being fixed in formaldehyde, so our desks were free from the clutter of our books and drawings binders and we were all wearing those now all-too-familiar purple gloves. My labmates were not excited about this lab...they were rather repulsed in fact, so I had been elected to do the "cutting" for this one. I remember thinking I was a pretty big nerd to not feel the same repulsion. In fact, I was actually intrigued by this miniscule monster. I had learned only minutes before that the females of this species can lay up to 200,000 eggs in a single day...a fun fact that has stuck with me even to this day. They weren't gross, they were fascinating. As I carefully drug the dissection pin down the length of the specimen's delicate tegument, I recall being curious about how such biological simplicity could lead such a complex life, and how something so...well...dissectionally "boring"...could be such a huge problem for so many people all over the world. Their anatomy was simple, but profoundly efficient. Their life cycle was strange and led to many questions that I would ponder over the next few years as I learned more about these parasites.

A pinned dissection of a female Ascaris.

This morning I was thinking about what to post for this week, and I realized that I had never posted anything about this creature, which in all fairness was the first creature to spark my interest in parasites. So let's talk about it!

Not long ago, I learned that this worm has a common name...which I had never heard before, surprisingly.  It is known in other places, especially in Europe, as "the maw-worm".  The word "maw" has deep roots dating back to both the Old English "maga"and the Middle English "mawe" both referring to the stomach or the belly.  Today, the word is more often used to describe the upper digestive tract, especially the mouth of a particularly ravenous animal. As we discuss the life cycle of this animal, keep both definitions in mind. But first things first.

Taxonomy
Ascaris lumbricoides belongs to kingdom Animalia and to phylum Nematoda (roundworms). As roundworms, they lack circulatory and respiratory systems and have a cuticle that is shed during successive growth stages.  This last characteristic is why these animals are thought to be more closely related to arthropods than to flatworms or segmented worms.  This species is further classified under the class Rhabditea along with other parasitic nematodes such as threadworms and pinworms. They exist in the order Ascaridida on the basis of having three prominent lips, lots of cuticular sensory structures called caudal papillae, and lateral external labial papillae. These worms are placed in the family Ascarididae, which it shares with the famous dog parasite, Toxocara canis.

Morphology

Posterior end of a male A. lumbricoides.

I won't got into too much detail here, but I will mention that these animals are quite large compared to other nematodes. Males typically range from 15cm-31cm in length and possess a distinctly curved posterior end. They are about 2mm-4mm in girth and have a few little spicules on their distinctive hook that are used for copulation.  The females are much larger, measuring between 20cm-49cm in length and 3mm-6mm in girth. Her ovaries extend the length of her body and her uterus is split into two parallel elongated structures that may hold as many as 27 million eggs at a time.

The eggs of these animals are particularly fascinating.  They can be oval or round and appear to have a bumpy outer shell.  This bumpy layer is comprised of proteins and is referred to as being "mammillated", which is really just a fancy word for bumpy. The lipids in the layer beneath the proteins in the egg shell are largely ascarosides.  Ascarosides are glycosides (sugars + alcohol + glycosidic bond) which give the shell its incredible powers of impenetrability. The only things that can pass through such layers are gases and lipid solvents. This gives them a resistance to a variety of chemicals that one parasite text book referred to as "almost legendary". These eggs have been known to remain viable in formalin, potassium dichromate, hydrochloric acid, nitric acid, acetic acid, and even sulfuric acid. (*Note* The acids were at 50% solutions, not at full strength, but that's still pretty amazing!) There have been documented cases of these eggs remaining viable after 10-12 years in the environment. The eggs are sometimes carried accidentally by cockroaches and other household pests that may dwell in contaminated soils. (Another reason I hate cockroaches.)

Life Cycle
The life cycle of these worms starts with their impervious eggs being shed in the feces of a human (or pig) host into soil.  While in the environment, juvenile worms will begin to form inside of the protective egg shells of fertilized eggs.  The juveniles will undergo a series of life stages, all inside the egg, before the egg becomes infective. At this point, a person (or pig) eats fruits or vegetables that are contaminated with egg-laden soil or drinks water with similar contamination.  Sometimes the eggs can even become airborne under the right conditions and infect via the nasal passages of humans. The eggs travel down into the stomach, where they continue to be impervious to the acids of the stomach, and on into the small intestines.  The eggs then hatch releasing the juvenile worms who then penetrate the intestinal walls to hitch a ride in the hepatic portal system. The now fourth-stage worms reach the lungs and penetrate through the alveoli.  They move up through the bronchiole tubes and into the trachea before being coughed up and re-swallowed back down into the esophagus. Once back in the small intestine, the worms mature, mate, and start pumping out eggs to start the cycle over.

The question I have, which is a question other more experienced biologists still trying to answer, is why the long journey out of the small intestine only to wind back up in the same place? Why not just stay there and mature in a safer environment? Some think this odd behavior is something that is a relic of some evolutionary adaptation with origins much further back in time. It makes me think of a sort of parasite walk-about. Where juveniles must embark on a perilous journey through our bodies in order to prove they have the ability to survive our dangerous immune system.  Upon returning home, they are given the privilege of mating and passing on their superior genes to the next generation of survivalists. (I feel like I could make a cartoon out of this...)

Ascariasis

A view of Ascaris within a small intestine.

The infection of a person with these worms is termed ascariasis.  Some of the bigger issues associated with infection occur when juveniles stray from their path to the lungs and die in other organs like the spleen or liver.  This can cause immune responses such as inflammation in these areas. Juveniles have also been known to migrate into developing fetuses through placental walls of expectant mothers.  The worms that manage to make it to the lungs cause hemorrhaging of lung capillaries, which becomes more severe in heavy infections.  With heavy parasite burdens, some people suffer from pulmonary edema and air-space clogging. Dead lung tissue and white blood cells may accumulate to create Loeffler's pneumonia (a.k.a. Ascaris pneumonitis).  If  unchecked, this can lead to diseased lungs that invite bacterial infections and could result in death.

A removed section of intestine that was
cut open to reveal blockage by these worms.

This worm might occasionally suck blood, but most of the time it just sticks to absorbing liquids from intestine. With enough worms, this can lead to malnutrition or underdevelopment.  It can also impair cognitive abilities in children. Most hosts experience abdominal pain, rashes, insomnia, asthma, and/or eye pain.  With massive infections, the intestines can become blocked by these worms, which is a fatal condition.  Adults will also sometimes wander out of the intestine to cause strange problems elsewhere in the body.



Diagnosis
Currently, there's no good way to identify juvenile stages of this parasite within a patient's body. Juveniles can be identified from sputum, but only by technicians who recognize them as being such. Fecal examinations can reveal eggs after worms have reached maturity and begun laying eggs. The symptoms described above can lead to a suspicion of ascariasis, but aren't enough for a full diagnosis alone.


Treatment

The choice drug for treating ascariasis is Mebendazole.  This drug binds with tubulin (a structural protein) and essentially paralyzes the muscles and intestinal walls of the worms. Ivermectin (a de-worming agent) is also used in some cases, as is Nitazoxanide (a drug for treating cryptosporidia). In cases of malnutrition, supplements are often administered as well. I have heard of people undergoing surgery to remove partial intestinal blockages due to these parasites, but I haven't actually read anything on that particular subject, so I don't know how often that actually happens.

The Moral of the Story
Wash your hands...especially if you've been playing in nightsoil (soil mixed with human feces). Also, don't use nightsoil as a fertilizer for your crops (don't laugh, many parts of the world do this)...and for God's sake, wash your fruits and vegetables well! This isn't something we worry about too much here in the states because ascariasis is found more often in tropical regions, but don't think we are immune here.  Just a few weeks ago someone brought into a local parasite lab a worm that their son had passed right here in Nebraska. The worm was a nice-sized female, and upon dissection she was found to have fertilized eggs, meaning the boy also had at least one male still inside of him. (Don't worry, I'm sure the good parasitologists recommended the parent get ahold of some Mebendazole.) The theory is that he got this from working on a pig farm.  Pigs carry these worms in the same way that humans do...in fact, the species known to infect pigs (Ascaris suum) is so similar to A. lumbricoides that some people argue these are actually the same species! So again...keep those hands clean!

The Other Moral of the Story
It's funny how some things stick in your mind. As I advanced through school after the day I opened up that worm I fell more and more in love with biology. I went from wanting to be a psychologist, wanting to do genetic engineering, to wanting to be a herpetologist, and finally to wanting a career as a parasitologist. The progression was slow and meandering, but I can still look back on my freshman year in Zoology Lab...to that exact day learning about nematodes....and it becomes clear that I was meant to be a parasitologist all along. I guess it just took meeting other parasitophiliacs to convince my brain of what my heart must have already known. <3

A throw-back to nematode-day of General Zoology Lab, which I took as a freshman, then taught as a grad-student.  The top left shows a male above a female to show their dimorphism. I'm not sure about the top right, so I won't speculate. The bottom left is a cross-section through a male showing the intestine surrounded by the testes and other reproductive organs.  The bottom right is a cross-section through a female showing the intestine (bacon-looking strip), uteri (the two big round structures), and ovaries (other round structures).  I remember we could always tell the male from the female cross-section by looking for the "eggs and bacon" or the "smiley face" in the female. :p

As You Wish-A Post for Friends, Family, and Readers

Okay everyone, sorry that I've fallen behind in posting.  The last few weeks have been pretty busy between my advisor leaving for Brazil (and me getting everything wrapped up before he left) and dealing with a side project that sort of consumed me last week. 

As some of you may know, I had an encounter with a man in a coffee shop.  The encounter began cordially enough...the man was sitting at the table with some friends I met a while back who meet once a week to discuss positive psychology. As I approached them with my delicious mug of Moroccan mint tea, I heard them discussing (or rather this man lecturing) about faith, hope, and love. I smiled thinking that this  would be a pleasant conversation....I was in for a surprise.  One of the men (the one in charge of these meetings) had to leave a little early (by "early" I mean early for him...we had already exceeded the one-hour time slot for this group discussion and had all opted to continue discussion outside of this scheduled discussion) so he excused himself and off he went, leaving me, the retired physicist (let's call him "D"), and the man still rambling (let's call him "R"). The conversation took an odd turn as R began to describe why he felt churches should be more exclusive and not let in people who do drugs and other such characters. I disagreed, but my opinion was barely noted before R continued ranting. As the rant evolved, somehow we got on the subject of homosexuality. At this point, the high and mighty R asserted that homosexuality was "unnatural".

I interjected, correcting him with a simple, "No it isn't." 

This comment sent in soaring into a rage of hellfire and brimstone and culminated with him telling me "You don't know what you are talking about". 

His comment unearthed within me a fury I hadn't realized dwelled within me.  I leaned forward assertively and got right in his face as I said, "I have two degrees in biology, I DO know what I am talking about."

 The man glared at me as I sat back into my seat and asked, "How old are you?"

I responded with my age only for him to assert that he was "3 times your age" (the guy couldn't have been any older than late 50s or early 60s) and that I couldn't possibly know more than him because I was younger. D interjected with a quick, "So you are in your 70s?" I asked if R had ever studied biology or the natural world....I asked if he had any degrees in the subject, to which he responded that he had a "degree from the university of life" and that he "had been a father and knew homosexuality was unnatural"....both excellent qualifications for discussing the subject at hand. O.o

This went on and on....he rambled about things that weren't pertinent to the discussion and tried to assert that they formed the basis for his argument. He confused gender identity issues with sexual identity issues, he claimed the bible and God himself said homosexuality was unnatural, and he said he had gay friends and loved them as people, but didn't believe they should be married because they would ruin the institution of marriage (though somewhere in there he revealed that he was divorced...one of those damn gays must have ruined his otherwise perfect marriage). Here D and I were, trying to get a word in, but maintaining a calm demeanor as R flew off the handle and caused a scene that had people all over the shop staring at us.  R challenged me to find "one shred of scientific proof" that homosexuality exists in nature.  All I could think was CHALLENGE FREAKING ACCEPTED!

After R left, D and I discussed the issue in a more civil manner where both of our opinions (though they were similar) could be voiced.  We also had one of the barista come over and tell us that he admired our patience with dealing with R. Over the next week, I spent more time that I intended searching the literature for examples of homosexuality in nature.  There was certainly no shortage of such evidence, in fact, I had to choose which studies to include in my report for R and which to just read for funzies. I learned a lot....it's amazing what you find when you look more intensely at a subject. 

The next week I waited for R at the coffee shop. I even made it a point to arrive early than I am usually able to arrive to make sure I wouldn't miss him. He never showed up. I was there from noon until a little after three and there was no sign of him, so my 23 page document remained in my backpack, along with my Principles of Biology textbook, flagged with passages touching on the subject from various chapters. Several friends and family members have requested to read this document, so I decided to post it here.  I know this isn't dealing with parasites themselves, but I believe that ignorance is parasitic, so in a metaphorical sense, this qualifies for the blog's theme. Plus it's my blog, so bite me.

The following is my report to R. This has been somewhat edited from it's original content to protect my own privacy in the event of pissing off someone crazy (and probably angrily ignorant), but I promise to try and leave it as untouched as possible. Be warned, it's kind of a long read. Also, please keep in mind that I wrote this in a week, so don't judge too harshly! Without further ado:

Authentically Natural: An Examination of Homosexuality as a Component of the Natural World

By: Me :)

INTRODUCTIONS

Who is this 26-year-old punk biologist?

            When we officially met for the first time last week, you made several incorrect assumptions about me. First, I must apologize for accidentally deceiving you. I recently had a birthday and I’m not used to calling myself 26 yet. So, I’m not 25…sorry about that. The way I figure, if we are going to have a civil conversation, we should know more about one another.  Here’s who I am. 

            I’m a 26-year-old Christian woman raised on a farm in a small town in Texas. Despite not having a lot of money growing up, I was extremely active in my community and in high school activities. I was an athlete for a short period of time (basketball, cross-country, track, and long jump). I was an artist in many different ways (musician, thespian, prose orator, poet, writer...I also dabbled in a number of craft-type works of art). I loved science as a general subject…it was always my favorite subject. Biology held my fascination the most of any of the branches of this subject. I competed in U.I.L Science along with a multitude of other academic competitions. I also loved promoting school spirit by serving as my school’s mascot for the last two years of high school. I graduated in 2005 as the class valedictorian. I remember praying as I prepared for my speech. I asked God to give me the right words, and as always, my God delivered.  In my speech, I quoted one of my favorite songs by Semisonic. The quote was “Every new beginning comes from some other beginning’s end”. I knew that these words were perfect for such a speech, but I didn’t know just how often they would return to resonate throughout my life.

            As this chapter of my life ended, I began a new chapter as a college student. I learned many things over the next four years. I learned more about the natural world and fell in love with it for its fascinating complexity. I learned that I didn’t know nearly as much about this subject as I had once thought.  I also learned that there were a lot of other things I didn’t know. I made lots of new friends and embraced a diversity of people that I had never been exposed to before. I learned about other cultures and other races. I learned about other faiths and other political viewpoints. I learned about people by not judging them and by actually taking the time to get to know them. I met gay people, lesbian people, transgendered people, and asexual people. I’d like to emphasize that I didn’t meet “gays” or “lesbians”, I met people. These people were interesting and taught me that there were more to them than I had ever realized. I’ve always felt like I was a compassionate person, but these new friends helped me to realize just how uncompassionate I had been towards people who were different from me. I was never outright mean to anyone, but I certainly had my prejudices. I’m not proud of this fact, but that doesn’t make it any less true. I am proud that I was mature enough to admit this fact and after intense prayer, I feel as if I have truly repented of my judgmental sins. I know in my heart that God blessed me with the ability to analyze information critically and to use that information to rationalize things that don’t make sense to me. I firmly believe that he sends people into our lives for a reason. Jesus was known as the great teacher, so it makes sense that we are all students, and that we all have lessons to learn. But like any good student, we have to keep our minds and hearts open, and we can’t fall asleep when we don’t like the subject matter if we actually want to learn anything.

            Getting back to college, I graduated in May 2009 with a Bachelors of Science in Organismal Biology with a second major in History (the majority of my history classes were in U.S. history, but were still generally well-rounded). I began graduate school the following August. I finished my Masters of Biological Sciences in May of 2012. A few months previous I had received my acceptance letter from a PhD program to which I had applied. I first laid eyes on my new home-city in June when we came to look for a place to live and for my fiancé to apply for jobs in our future new home. In July I married the love of my life after dating for four years, and then we jetted off to a resort in Mexico for what most experts would have to agree was the most amazing honeymoon anyone has ever had ever. In August, we packed up our belongings and headed up to this city. I began my work as a Ph.D. student a few weeks later. So many new beginnings born from the end of this chapter of my life.

            I am now studying ancient parasitism under a world expert in the field of Archaeoparasitology (in fact, he coined the term itself). I’ve learned a great deal more since moving here. My knowledge of parasites and the people who study them has at least tripled since I arrived last August. As before, I’ve made a lot of new and diverse friends. I’ve learned even more about how different people are and how wonderful those differences can be. Some of my new friends are homosexuals. They are such amazing and fun people! They throw great parties and always go out of their way to make people feel included at group events. I can’t even count the number of gay men I have met in the last few months because if we are at a gathering, they always make it a point to introduce themselves and ask me about what I do. Such a simple act of kindness is appreciated when you don’t know many of the people surrounding you.  After meeting you last Friday, I attended a birthday party for a gay friend. I wore a pretty, full-length dress and pair of adorable shoes. We ended up walking more than we had expected to be walking and my feet began to hurt terribly. I mentioned my pain to my friend and without much thought he offered to run a few blocks back to another friend’s apartment to get me some flip-flops, but I didn’t want to split up the group on my account. Then my friend did something totally unexpected…he offered to swap me for his flat, comfy-looking shoes. I didn’t think he was serious, but he was. He wore the heels even after some fraternity boys walking along the sidewalks downtown called him a “faggot”. He didn’t care. He didn’t want me to be in pain anymore. He wore those shoes until my feet had recovered and then we swapped shoes again so he could go dance with his friends for his birthday. This was the most selfless act of love anyone other than my husband had done for me in years. Words cannot express how blessed I am to know this man, nor can they adequately express how thankful I am that God opened my eyes and my heart so many years ago.

            I suppose this all boils down to me needing you to realize that I’m not just some punk that pissed you off with bullshit last week. I am a person who has been fascinated by the natural world all of my life. I have spent the better part of the last decade dedicating my life to studying biological systems and the organisms that comprise them. I moved to a new state where I barely knew anyone with my wonderfully supportive husband to become better educated about my passion, and to build a career as a biologist. I am qualified to discuss matters of biology despite my age and your perception of the correlation that is, in all actuality, non-existent between the two. I am also an avid supporter for the rights of homosexuals. I support their civil rights not because some politician told me to, not because my parents told me to, not because my priest told me to…but because I got to know homosexuals. I also support their rights because I have logically analyzed both sides of arguments regarding the rights of homosexuals over the years and the only rational explanation from legal, scientific, and religious viewpoints was that they have the right to enjoy the same lives, liberties, and pursuits of happiness as any other American. 

EXAMINING HOMOSEXUALITY

A Biological Perspective

            I suppose the best way to start is to begin with the subject about which I know the most. First, let us define a few words so that we are all on the same page about what those words mean.

Gender Identity--This refers to a person’s sense of and subjective experience of their own gender. Whether a person identifies themself as being male or female is not a function of their sex chromosomes. Rather, gender identity is a function of one’s own inner perceptions and feelings about their gender.

Sexual Identity--This refers to how one thinks of oneself in terms of whom one is romantically or sexually attracted to. Like gender identity, this is not a function of sex chromosomes, but rather a function of physical and psychological attraction.

Sexual Orientation--This refers to an enduring personal quality that inclines people to feel romantic or sexual attraction to persons of the opposite or same sex or gender or to both sexes or to more than one gender. These attractions are generally called heterosexuality, homosexuality, bisexuality, or asexuality, but there are subcategories within some of these more broad groupings. Generally, there are three components that make up one’s sexual orientation: Sexual attraction, sexual behavior, and sexual identity. There is no simple cause for sexual orientation. Research suggests that biological factors such as genetics and biochemistry as well as environmental factors influence sexual orientation. Sexuality has also been shown by research to be fluid, and to be existent in various gradations rather than existing dichotomously.

Transgendered--This refers to individuals who have tendencies that are different from the conventionally accepted gender roles. Transgendered individuals feel there is a discrepancy with their assigned gender and their internal sense of gender. These individuals typically do not seek to change their bodies surgically. This is a state of a person’s gender identity and has nothing to do with one’s sexual orientation.

Transsexual--This refers to individuals who do not identify with the gender they were assigned at birth.  They often (but don’t always) seek surgery in order to make their bodies reflect their gender identity. Again, this is a function of gender identity, not sexual orientation.

Intersex (a.k.a. hermaphroditism in non-human species)--This refers to a variation in sex characteristics including chromosomes, gonads, and/or genitals that do not allow an individual to be distinctly identified as male or female. Being an intersexed individual may include genital ambiguity, and/or combinations of genotypes or phenotypes other than XY or XX and their associated phenotypes.

Gynandromorph--This refers to an organism that contains both male and female characteristics. These animals have astonishingly distinctive demarcations between their male and female appearances.  Gynandromorphic individuals are found in various species of animals including spiders, butterflies, moths, lobsters, crabs, birds, and even small mammals.

Parthnogenesis--This is a type of asexual reproduction through which embryos develop without fertilization from sperm. Offspring are genetically identical to the parent individual.

            Okay, now that we all know what these words mean, let’s talk sexual diversity in nature.  There are over 1,500 species that have been observed displaying homosexual behaviors. (Bagemihl, 1999) Many instances of humans observing such behaviors were never formally documented or were outright rejected for fear of reprimand by the scientific community existing within societies not yet accepting of such concepts. However, the sexual diversity of the natural world remains a biological truth whether or not man choses to believe in its existence. 

            There are a variety of homosexual behaviors displayed by non-human animal species. These behaviors include mating rituals directed at members of the same sex, copulation with members of the same sex, displays of affection among members of the same sex, genital stimulation of members of the same sex without copulation, and even parenting of offspring by two members of the same sex. 

“The animal kingdom [does] it with much greater sexual diversity--including
homosexual, bisexual, and non-reproductive sex--than the scientific community
and society at large have previously been willing to accept.”
--Bruce Bagemihl, Ph.D. (Canadian Biologist and Linguist)--

            A plethora of species display such behaviors. (See Appendix 1-7).  Let’s start with insects. At least 11 species of dragonflies and damselflies have been documented as having mating damage on the heads of males in 20%-80% of a population. You see, these animals have an interesting way of engaging in sex. The males have little claspers on their abdomens that they use to grip the region behind the head of the females during copulation.  In the process, females contract “mating damage” to those bodily regions. Males do not use their claspers for defensive purposes. The discovery of mating damage on these animals indicates that they engage in homosexual coupling behaviors (Utzeri and Belfiore, 1990).  Bed bugs also have been shown to engage in homosexual mounting (Ryne, 2009). Fruit flies (Drosophila melanogaster) have been used to study the genetic basis of homosexuality. If a male of this species bears two copies of a particular allele within a certain gene, the male will mate exclusively with other males of the species (Gailey and Hall, 1989).  Later studies covered the alteration of brain structure in homosexual individuals (Yamamoto, et al., 1998). Other studies further examined this phenomenon in this species, but we won’t cover them further for our purposes. 

            Okay, but these are just insects, higher animals couldn’t possibly be homosexual, right? Wrong. Whiptail lizards (belonging to the family Teiidae) undergo parthenogenesis more often than they engage in sexual behaviors for reproductive purposes. For this reason, males are rare in many of these species. Often times, female will engage in homosexual behaviors in order to stimulate ovulation. Hormones are triggered by such behaviors and engaging in such behaviors have been shown to actually increase the success of asexual reproduction. Mating pairs will switch between “masculine” and “feminine” sexual positions and roles from one mating season to another.  Some geckos are also known to reproduce in a similar manner (Kearney, et al., 2005).  Female homosexuality has also been observed in American chameleons (Anolis) and male homosexuality has been observed in members of the family Iguanidae (Denniston, 1980).

            Still, those are lizards, surely there’s not more advanced animals that are homosexuals.  Wrong again. Birds have been shown to display both homosexual and transgender behaviors. The list of birds that display such behaviors is extensive to put it mildly. Everything from black swans to ibises, to gulls, to mallards, to pigeons, and vultures can be found on this list. Flamingos and  penguins have been known to form homosexual committed relationships in which same-sex birds engage in sex, travel together, live together, and even raising young together (Smith, 2004). Almost a quarter of all black swan (Cygnus atratus) couples are homosexual. Male homosexuals will sometimes form temporary threesomes with a female, and then drive her from the nest in order to raise the offspring without her help (Goudarzi, 2006; Imaginova, 2007).  A South American bird (Rupicola rupicola) is known to have populations with upwards of 40% of the population engaging in regular homosexual activities.  Some of these birds never copulate with members of the opposite sex (Bagemihl, 1999; Imaginova, 2007).  Just like with insects, I could go on, but I think I’ve made my point about birds and homosexuality.

            Still thinking all of this evidence doesn’t apply? How about we look at mammals?  Domestic animals such as sheep, cattle, and horses have been known to engage in homosexual activities, as have pets such as budgerigars, cats, and dogs (Bagemihl, 1999).   Ever wonder why dolphins are sometimes associated with lesbians?  Perhaps it is because at least two species of this animal have been observed performing homosexual (and heterosexual) acts of nasal sex (penetration of the blowhole).  Or perhaps it is because some bottlenose dolphin females have sexual encounters known as “beak-genital propulsion”, in which a female inserts her beak into another female’s genital opening while swimming forward. (Norris and Dohl, 1980).  Males of this species have been known to rub their genitals together, swim belly to belly, and even engage in anal sex (Wells, 1995). Dolphins have also engaged in group sex of both homosexual and heterosexual compositions.  Some dolphins will even have sex with dolphins of other species.  It is also evident that dolphins have sex for pleasure in addition to sex for procreation (Bagemihl, 1999; Sylvestre,1985).

            Let’s move out of the ocean and onto land.  Some of the first homosexual behaviors observed in animals were among wild rams.  Male rams were seen readily mating with other males even when females were readily available for coitus.  These males seemed to refuse to mate with the females despite seasonal conditions.  A behavior known as “foreleg kicking” is part of the mating ritual in these animals.  This behavior involves the male gently tapping their forelegs on the genitals of the female to prepare for intercourse.  This behavior has been documented between males.  As many as 10% of these rams displayed this and other homosexual mating behavior in the populations observed (LeVay, 2011).  Foreleg kicking is also a part of mating rituals in other animals.  In kobs (a type of African antelope), females are often observed performing foreleg kicking and mounting other females.  As in rams, these behaviors occur even during the breeding season when there are plenty of males available for procreating (Imaginova, 2007; Bagemihl, 2000).

            The American bison has been known to have courtship, mounting, and full anal penetration between bulls (Bagemihl, 2000).  Native Americans even had ceremonies reenacting this behavior to make sure the buffalo would be back in the next year. Speaking of gentle homosexual giants, elephants and giraffes also engage in same-sex mounting and pair bonding, as demonstrated by shows of affection such as d trunk playing and necking. Heterosexual relations among these animals are typically fleeting, while homosexual partnerships may last for years (Bagemihl, 1999).  Lions, monkeys, hyenas, polecats, moose, rabbits, mice, foxes, zebras, and apes all have homosexual activity among populations.  Homosexuality is particularly high in giraffes…sometimes reaching as much as 90% among male in a population (Bagemihl, 1999; Coe, 1967).  

            Reports of primates displaying homosexual behaviors are numerous, to put it mildly.  Such behaviors occur more often than incidentally, and should not be dismissed as aberrations in sexual norms among these animals (Small, 1993).  Baboons have been known to form monogamous homosexual relationships.  Some of these relationships have been documented as lasting up to 6 years in wild populations.  Homosexual mounting has been reported as being common in various species of monkeys and has been studied in rhesus monkeys, stumptail macaques (Mitchell, 1979), Japanese macaques (Mahlman and Chapais, 1988), and others.  Homosexuality also exists among chimpanzees, mountain gorillas (Yamagiwa, 1987; Yamagiwa 1992; Edwards and Todd, 1987), pygmy chimpanzees (Savage and Bakeman, 1978), siamangs, and gibbons (Edwards and Todd, 1987).

            Going a step further, let’s touch briefly on other forms of sexual diversity in nature.  Some species are completely asexual, for example, sea urchins never engage in sexual acts at all and rely on other methods for reproduction.  Remember that word gynandromorph? I won’t go over it again, but these individuals are ideal examples sexual diversity in nature.  Bisexuality occurs within a number of species naturally, and not just in those that are hermaphroditic.  As you’ve already been told, animals such as elephants and giraffes have fleeting heterosexual relationships that turn into a more monogamous type of relationship outside of the breeding season when homosexual relationships are resumed or begun between two males.  This is a sort of conditional form of bisexuality.  Some species are bisexuals in a much more strict sense of the word.  

            Bonobos are incredibly sexual primates.  The majority of their day is consumed with sexual intercourse or other sexual acts.  The bonobos aren’t having this much sex just to procreate, they use sex for a variety of purposes outside of reproduction.  Females have been observed choosing genital-to-genital rubbing with other females over engaging in sexual activities with a male (Small, 1993).  Sometimes sex is used to end arguments over food.  These animals have been observed fighting over food, then engaging in sexual activities, followed by sharing of the food between the post-coital couple. Age and fitness do not seem to influence the decision to have sex in these animals. These are not monogamous animals, but they do show signs of affection before, during, and after sexual encounters whether they be of a heterosexual or a homosexual nature. These animals typically engage in sex facing one another, something previously only seen in humans.  Sex is a vital tool for these animals that is used to maintain a peaceful, affectionate, corporative, bisexual, society.

            Now that you know that sexual diversity does, in fact, exist in nature, let’s talk about some of the biological mechanisms that impact a human’s sexual orientation.  I honestly tried very hard last week not to laugh when you requested that I present a “gay gene”, but that reaction wasn’t very Christian of me. I shouldn’t have laughed, even inwardly, at your ignorance of this particular subject matter. Please accept my humble apology, and allow me explain first, why this phrase is, in and of itself, asinine.  Afterwards, I will site a few studies published in peer-reviewed, scientific journals in which the internal biological factors of homosexuality are examined.

            The presence of the concept of a “gay gene” reveals just how little the general public understands about genetics and the way that genes function. A genetic characteristic as complex as one’s sexual orientation is not going to be controlled by a single gene.  In humans, our eye color alone is controlled by 16 different genes, with two playing the leading role in iris color determination.  Think about it, if it takes 16 genes to determine the color of your eyes, how many genes would it take to determine sexual attraction? No one has been able to determine exactly how many genes control sexual orientation, but there is significant evidence to suggest that sexual orientation is based, at least in part, on genetic components. (Thornton, et al., 2009; Garcia-Falgueras and Swaab, 2010; Bogaert and Skorska, 2011) 

            Hormones and neurotransmitters have also been shown to play a role in sexual orientation. Studies of mice have shown that 5-hydroxytryptamine (5-HT) is required for male sexual preference (Liu, et al., 2011).  This neurotransmitter is more commonly known as serotonin, and is believed to be involved in our feelings of happiness and well-being.

“Here we report that the neurotransmitter 5-hydroxytryptamine (5-HT)...Wild-type male mice preferred females over males, but males lacking central serotonergic neurons [such as those releasing 5-HT] lost sexual preference although they were not generally defective in olfaction or in pheromone sensing...These results indicate that 5-HT and serotonergic neurons in the adult brain regulate mammalian sexual preference.”

--Liu, et al., 2011--

            Other studies involving mice have shown that disabling the fucose mutarotase gene (which adjusts the brain’s exposure to estrogen) causes female mice to behave as if they were males when they reach sexual maturity (Park, et. al., 2010).  This is similar to the study looking at induced homosexuality in fruit flies mentioned earlier.  Although these studies focus on single genes or particular neurotransmitters, the researchers acknowledge that other genes and multiple neurotransmitters as well as hormones must play a role in these complex behaviors.  

            Some researchers believe that birth order may influence the likelihood of homosexuality among males.  The association between birth order and male sexual orientation is termed “the fraternal birth order effect” (Valenzuela, 2010). The cause for this effect is unknown, however, researchers have a working theory that involves the maternal immune system.  According to this theory, the first time a woman becomes pregnant with a male, her body’s immune system reacts to it as if it is a foreign body, which is often why pregnancies with males are more difficult that pregnancies with females.  As the pregnant mother-to-be’s body releases antigens and antibodies to protect the mother, the immune system “learns” how to identify males.  With successive pregnancies involving male fetuses, the body knows how to identify these male threats and begins to produce less testosterone in an attempt to subdue the threat.  The more boys a mother gives birth to, the higher the chance that her next son will be homosexual.  (Blanchard and Bogaert, 1996; Blanchard and Klassen, 1997; Blanchard, 2001; Blanchard, 2004).

            Another interesting study conducted in the early 90s showed that the hypothalamus of homosexual males was smaller than that of heterosexual males.  This structure is used to regulate sexual behavior.  The size of this structure was equivalent in homosexual males with the same structure in heterosexual females (LeVay, 1991; Angier, 1992). Other anatomical studies showed that the anterior commissure of homosexual men is larger than the structure in both heterosexual men and women.  This structure is a bundle of nerves that allow for both halves of the brain to communicate with each other (Allen and Gorski, 1992). Studies have further shown hormonal differences between homosexuals and heterosexuals (West, 1977).  A particularly well-written article expands on these and other aspects of homosexuality in nature.  I suggest reading Homosexuality: A Paradox of Evolution by Preston Hunter.  Keep in mind that this was written in 1994 and that many more studies have come out since its publication.

A Psychological Perspective

            On Friday you asserted that being a homosexual was a choice.  Now that we have examined the biological reasons why such a statement is untrue, let us look briefly at homosexuality from a psychological point of view.

            For many years people used to believe that homosexuality was a choice.  The Diagnostic and Statistical Manual of Mental Disorders (a.k.a. “The DSM”) once listed being gay as a disorder known as “androphilia” and being a lesbian as a disorder known as “gynephilia”.  Similar terms were also once used to refer to transgendered people (“auto-gynephilia/auto-androphilia”).  All terms associated with homosexuality were removed from the DSM in 1973, but were replaced by the phrase “ego-dystonic homosexuality” which addressed a “lack of heterosexual arousal” coupled with a “persistent distress from a sustained pattern of unwanted homosexual arousal”.  This new diagnosis only applied to homosexuals who didn’t want to accept their sexual orientation.  This came under harsh criticisms by some psychoanalysts who still believed homosexuality could be treated with conversion therapy.  After years of debate among professionals in the field, the diagnosis was removed completely from the DSM in 1986.

            Since that time, many other professional organizations have stated that sexual orientation is not a choice and that it is not something that can be changed.  These organizations strongly oppose attempts at conversion therapy and instead advocate for families and friends of homosexuals to be supportive of their loved one’s innate sexual identity.  These organizations include: 

• ·         The American Psychological Association (publish the DSM)
• ·         The National Association of Social Workers
• ·         The American Psychiatric Association
• ·         The American Academy of Pediatrics
• ·         The American Psychoanalytic Association
• ·         The American Medical Association

            Mental health professionals have agreed since the 1970s that homosexuality is a normal, natural form of human sexual orientation (APA, 2009).  Homosexuality was declassified as a mental disorder first by The American Psychiatric Association in 1973 and then by The American Psychological Association in 1975 (Bayer, 1987).  Many other organizations did the same in the years that followed.  By 1990, homosexuality was declassified by the World Health Organization.

           

            Many studies have looked at sexual orientation from a psychological perspective, but few are more famous that the Kinsey studies of the 1940s and 1950s.  The studies showed that sexual orientation was not as black-and-white as people had once believed. In fact, most people fall somewhere between exclusively heterosexual and exclusively homosexual.  These studies culminated in the creation of a scale known as the Kinsey Scale.  This scale is depicted below.

Rating	Description
0	Exclusively heterosexual. Individuals make no physical contact which results in erotic arousal or orgasm and make no psychic responses to individuals of their own sex.
1	Predominantly heterosexual/incidentally homosexual. Individuals have only incidental homosexual contacts which have involved physical or psychic response or incidental psychic response without physical contact.
2	Predominantly heterosexual but more than incidentally homosexual. Individuals have more than incidental homosexual experience and/or respond rather definitely to homosexual stimuli.
3	Equally heterosexual and homosexual. Individuals are about equally homosexual and heterosexual in their experiences and/or psychic reactions.
4	Predominantly homosexual but more than incidentally heterosexual. Individuals have more overt activity and/or psychic reactions in the homosexual while still maintaining a fair amount of heterosexual activity and/or responding rather definitively to heterosexual contact.
5	Predominantly homosexual/only incidentally heterosexual. Individuals are almost entirely homosexual in their activities and/or reactions.
6	Exclusively homosexual. Individuals who are exclusively homosexual, both in regard to their overt experience and in regard to their psychic reactions.

            This scale has been adapted by many other researchers and is the predecessor to more commonly used scales found in modern psychological and psychiatric research. More modern techniques include the Klein Sexual Orientation Grid (KSOG), which is more multidimensional, as well as Sell Assessment of Sexual Orientation (SASO), which measures sexual orientation on a continuum and is meant to provoke discussion rather than to provide a final solution (Klein, et al., 1985; Sell, 1997). Assessing one’s sexual orientation typically involves assessing three components: Sexual Attraction, Sexual Behavior, and Sexual Identity.

            I believe that you also mentioned something about being opposed to same-sex parenting.  While you are entitled to your own opinion, I felt it would be pertinent to point out that many (almost all) social scientists agree that this form of parenting is not psychologically damaging to children.  There is no scientific literature supporting the assertion that heterosexual parents are inherently better than homosexual parents.  In fact, many organizations regularly issue reports in support of the rights for gay and lesbian parents.  These organizations include the following:

• ·         The American Academy of Pediatrics
• ·         The American Academy of Child and Adolescent Psychiatry
• ·         The American Psychiatric Association
• ·         The American Psychological Association
• ·         The American Psychoanalytic Association
• ·         The National Association of Social Workers
• ·         The Child Welfare League of America
• ·         The North American Council on Adoptable Children
• ·         The Canadian Psychological Association (CPA).       

CONCLUSIONS

            I suppose it is about time that I wrap up this report. After all, every new beginning comes from some other beginning’s end.  This is the end of my report to you, but I anticipate that it is a new beginning for you and your understanding this subject from a scientific perspective.  I hope that this new-found knowledge inspires you to delve deeper into the science of homosexuality. I’m not looking to change your opinion on homosexuality in terms of whether you see it as “right” or “wrong”, but I hope I have educated you enough on the subject for you to realize that homosexuality is natural in both a biological sense and in a psychological sense.  

            Throughout this report, I have demonstrated, using sound, scientific evidence, that a great variety of animals display homosexual behaviors and also that many of these animals form monogamous homosexual partnerships. Homosexual parenting has also been observed in nature and the offspring from such parenting strategies seem to fair just as well as offspring raised by heterosexual parents.

            I have also presented a number of studies discussing the biological and psychological aspects of human sexual orientation. As discussed previous, many factors come into play with the development of an individual’s sexual orientation. Many of these factors are not completely understood, but as research progresses, new insights regarding the causal effects of hormones, neurotransmitters, and genes begins to emerge. Advances in psychological and psychiatric research continue to show that sexual orientation is not something that one chooses, nor is it an aspect of one’s psyche that can be changed by “reparative” or “conversion” therapies.

            In conclusion, our sexual orientation is a function of our biology and wide variety of sexual diversity is present in the natural world of which we are a part.  Opposition to homosexuality and other non-heterosexual forms of sexual orientation are not valid from biological and psychological perspectives. Discrimination against individuals with these forms of sexual orientation is consequently not justified by these fields of science. Cultural and religious perspective may agree or disagree with homosexuality, but have no bearing on the scientific realities of this subject.

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Appendix I:
A List of Insects Displaying Homosexual Behaviors

·   Alfalfa Weevil ·   Australian Parasitic Wasp sp. ·   Bean Weevil sp. ·   Bedbug and other Bug spp. ·   Blister Beetle spp. ·   Blowfly ·   Broadwinged Damselfly sp. ·   Cabbage White (Butterfly) ·   Checkerspot Butterfly ·   Club-tailed Dragonfly spp. ·   Cockroach spp. ·   Common Skimmer spp. ·   Creeping Water Bug sp. ·   Cutworm ·   Digger Bee ·   Dragonfly spp. ·   Eastern Giant Ichneumon Wasp ·   Eucalyptus Longhorned Borer ·   Field Cricket sp. ·   Flour Beetle ·   Fruit Fly spp. ·   Glasswing Butterfly ·   Grape Berry Moth ·   Grape Borer ·   Green Lacewing ·   Hen Flea

·     House Fly ·     Ichneumon wasp sp. ·     Japanese Scarab Beetle ·     Larch Bud Moth ·     Large Milkweed Bug ·     Large White ·     Long-legged Fly spp. ·     Mazarine Blue ·     Mediterranean Fruit Fly ·     Mexican White (butterfly) ·     Midge sp. ·     Migratory Locust ·     Monarch Butterfly ·     Narrow-winged Damselfly ·     Parsnip Leaf Miner ·     Pomace fly ·     Queen Butterfly ·     Red Ant sp. ·     Red Flour Beetle ·     Reindeer Warble Fly   ·     Rose Chafer ·     Rove Beetle spp. ·     Scarab Beetle   ·     Screwworm Fly ·     Silkworm Moth

·     Southeastern Blueberry Bee ·     Southern Green Stink Bug ·     Southern Masked Chafer ·     Southern One-Year Canegrub ·     Spreadwinged Damselfly spp. ·     Spruce Budworm Moth ·     Stable Fly sp. ·     Stag Beetle spp. ·     Tsetse Fly ·     Water Boatman ·     Water Strider spp.

Appendix II:
A List of Other Invertebrates
Displaying Homosexual Behaviors

·         Blood-Fluke

·         Box Crab

·         Harvest Spider sp.

·         Hawaiian Orb-Weaver

·         Incirrate Octopus spp.

·         Jumping Spider and Some Select Yeast sp.

·         Mite sp.

·         Spiny-Headed Worm

·         Amoeba and Barneys

Appendix III:
A List of Fish Displaying Homosexual Behaviors

·         Amazon molly

·         Blackstripe topminnow

·         Bluegill Sunfish

·         Char

·         Grayling

·         European Bitterling

·         Green swordtail

·         Guiana leaffish

·         Houting Whitefish

·         Jewel Fish

·         Least Darter

·         Mouthbreeding Fish sp.

·         Salmon spp.

·         Southern platyfish

·         Ten-spined stickleback

·         Three-spined stickleback

Appendix IV:
A List of Amphibians
Displaying Homosexual Behaviors

·         Appalachian Woodland Salamander

·         Black-spotted Frog

·         Mountain Dusky Salamander

·         Tengger Desert Toad

Appendix V:
A List of Reptiles Displaying Homosexual Behaviors

Anole sp. Bearded Dragon Broad-headed Skink Checkered Whiptail Lizard Chihuahuan Spotted Whiptail Lizard Common Ameiva Common Garter Snake Cuban Green Anole Desert Grassland Whiptail Lizard Desert Tortoise Fence Lizard Five-lined Skink Gopher (Pine) Snake Green Anole Inagua Curlytail Lizard

Jamaican Giant Anole Laredo Striped Whiptail Lizard Largehead Anole Mourning Gecko Plateau Striped Whiptail Lizard Red Diamond Rattlesnake Red-tailed Skink Side-blotched Lizard Speckled Rattlesnake Water Moccasin Western rattlesnake Western Banded Gecko Whiptail Lizard spp. Wood Turtle

Appendix VI:
A List of Birds Displaying Homosexual Behaviors

·      Acorn Woodpecker ·      Adelie Penguin ·      American Flamingo ·      American Herring Gull ·      Anna's Hummingbird ·      Australian Shelduck ·      Aztec Parakeet ·      Bengalese Finch (Domestic) ·      Bank Swallow ·      Barn Owl ·      Bicolored Antbird ·      Black-billed Magpie ·      Black-crowned Night Heron ·      Black-headed Gull ·      Black-rumped Flameback ·      Black Stilt ·      Black Swan ·      Black-winged Stilt ·      Blue-backed Manakin ·      Blue-bellied Roller ·      Blue Tit ·      Blue-winged Teal ·      Brown-headed Cowbird ·      Budgerigar (Domestic) ·      Buff-breasted Sandpiper ·      Calfbird ·      California Gull ·      Canada Goose ·      Canary-winged Parakeet ·      Caspian Tern ·      Cattle Egret ·      Common Chaffinch ·      Chicken ·      Chilean Flamingo ·      Chiloe Wigeon ·      Chinstrap penguin ·      Cliff Swallow ·      Common Gull ·      Common Murre ·      Common Shelduck ·      Crane spp. ·      Dusky Moorhen ·      Eastern Bluebird ·      Egyptian Goose ·      Elegant Parrot ·      Emu ·      Eurasian Oystercatcher ·      European Jay ·      European Shag

·      Galah ·      Gentoo Penguin ·      Golden Bishop Bird ·      Golden Plover ·      Gray-breasted Jay ·      Gray-capped Social Weaver ·      Gray Heron ·      Great Cormorant ·      Greater Bird of Paradise ·      Greater Flamingo ·      Greater Rhea ·      Green Sandpiper ·      Greenshank ·      Greylag Goose ·      Griffon Vulture ·      Guianan Cock-of-the-Rock ·      Guillemot ·      Hammerhead (also known as Hammerkop) ·      Herring Gull ·      Hoary-headed Grebe ·      Hooded Warbler ·      House Sparrow ·      Humboldt Penguin ·      Ivory Gull ·      Jackdaw ·      Kestrel ·      King Penguin ·      Kittiwake ·      Laughing Gull ·      Laysan Albatross ·      Lesser Flamingo ·      Lesser Scaup Duck ·      Little Blue Heron ·      Little Egret ·      Long-tailed Hermit Hummingbird ·      Lory spp. ·      Mallard ·      Masked Lovebird ·      Mealy Amazon Parrot ·      Mew Gull ·      Mexican Jay ·      Musk Duck ·      Mute Swan ·      Ocellated Antbird ·      Ocher-bellied Flycatcher ·      Orange Bishop Bird ·      Orange-fronted Parakeet ·      Ornate Lorikeet ·      Ostrich

·      Peach-faced Lovebird ·      Pied Flycatcher ·      Pied Kingfisher ·      Pigeon (Domestic) ·      Powerful Owl ·      Purple Swamphen ·      Raggiana's Bird of Paradise ·      Raven ·      Razorbill ·      Red-backed Shrike ·      Red Bishop Bird ·      Red-faced Lovebird ·      Common Redshank ·      Red-shouldered Widowbird ·      Regent Bowerbird ·      Ring-billed Gull ·      Ring Dove ·      Rock Dove ·      Roseate Tern ·      Rose-ringed Parakeet ·      Ruff ·      Ruffed Grouse ·      Sage Grouse ·      San Blas Jay ·      Sand Martin ·      Satin Bowerbird ·      Scarlet Ibis ·      Scottish Crossbill ·      Senegal Parrot ·      Sharp-tailed Sparrow ·      Silver Gull ·      Silvery Grebe ·      Snow Goose ·      Steller's Sea Eagle ·      Superb Lyrebird ·      Swallow-tailed Manakin ·      Tasmanian Native Hen ·      Tree Swallow ·      Trumpeter Swan ·      Turkey (Domestic) ·      Victoria's Riflebird ·      Wattled Starling ·      Western Gull ·      White-fronted Amazon Parrot ·      White Stork ·      Wood Duck ·      Yellow-backed Lorikeet ·      Yellow-rumped Cacique ·      Zebra Finch (Domestic)

Appendix VII:
A List of Mammals Displaying Homosexual Behaviors

·   African Buffalo ·   African Elephant ·   Agile Wallaby ·   Amazon River Dolphin ·   American Bison ·   Antelope ·   Asian Elephant ·   Asiatic Lion ·   Asiatic Mouflon ·   Atlantic Spotted Dolphin ·   Australian Sea Lion ·   Barasingha ·   Barbary Sheep ·   Beluga ·   Bharal ·   Bighorn Sheep ·   Black Bear ·   Blackbuck ·   Black-footed Rock Wallaby ·   Black-tailed Deer ·   Bonnet Macaque ·   Bonobo ·   Bottlenose Dolphin ·   Bowhead Whale ·   Brazilian Guinea Pig ·   Bridled Dolphin ·   Brown Bear ·   Brown Capuchin ·   Brown Long-eared Bat ·   Brown Rat ·   Buffalo ·   Caribou ·   Cat (Domestic) ·   Cattle (Domestic) ·   Cheetah ·   Collared Peccary ·   Commerson's Dolphin ·   Common Brushtail Possum ·   Common Chimpanzee ·   Common Dolphin ·   Common Marmoset ·   Common Pipistrelle ·   Common Raccoon ·   Common Tree Shrew ·   Cotton-top Tamarin ·   Crab-eating Macaque ·   Crested Black Macaque ·   Dall's Sheep ·   Daubenton's Bat ·   Dog (Domestic) ·   Donkey ·   Doria's Tree Kangaroo ·   Dugong ·   Dwarf Cavy ·   Dwarf Mongoose ·   Eastern Cottontail Rabbit ·   Eastern Grey Kangaroo ·   Elk ·   Euro ·   European Bison ·   Fallow Deer ·   False Killer Whale ·   Fat-tailed Dunnart ·   Fin Whale ·   Fox ·   Gazelle ·   Gelada Baboon ·   Giraffe ·   Goat (Domestic) ·   Golden Monkey ·   Gorilla

·   Grant's Gazelle ·   Grey-headed Flying Fox ·   Grey Seal ·   Grey squirrel ·   Grey Whale ·   Grey Wolf ·   Grizzly Bear ·   Guinea Pig (Domestic) ·   Hamadryas Baboon ·   Hamster (Domestic) ·   Hanuman Langur ·   Harbor Porpoise ·   Harbor Seal ·   Himalayan Tahr ·   Hoary Marmot ·   Horse (Domestic) ·   Human ·   Indian Fruit Bat ·   Indian Muntjac ·   Indian Rhinoceros ·   Japanese Macaque ·   Javelina ·   Kangaroo Rat ·   Killer Whale ·   Koala ·   Kob ·   Larga Seal ·   Least Chipmunk ·   Lechwe ·   Lesser Bushbaby ·   Lion ·   Lion-tailed Macaque ·   Lion Tamarin ·   Little Brown Bat ·   Livingstone's Fruit Bat ·   Long-eared Hedgehog ·   Long-footed Tree Shrew ·   Macaque ·   Markhor ·   Marten ·   Matschie's Tree Kangaroo ·   Moco ·   Mohol Galago ·   Moor Macaque ·   Moose ·   Mountain Goat ·   Mountain Tree Shrew ·   Mountain Zebra ·   Mouse (Domestic) ·   Moustached Tamarin ·   Mule Deer ·   Musk-ox ·   Natterer's Bat ·   New Zealand Sea Lion ·   Nilgiri Langur ·   Noctule ·   North American Porcupine ·   Northern Elephant Seal ·   Northern Fur Seal ·   Northern Quoll ·   Olympic Marmot ·   Orangutan ·   Pacific Striped Dolphin ·   Patas Monkey ·   Pere David's Deer ·   Pig (Domestic) ·   Pig-tailed Macaque ·   Plains Zebra

·   Polar Bear ·   Pretty-faced Wallaby ·   Proboscis Monkey ·   Pronghorn ·   Przewalski's Horse ·   Puku ·   Quokka ·   Rabbit ·   Raccoon Dog ·   Red Deer ·   Red Fox ·   Red Kangaroo ·   Red-necked Wallaby ·   Red Squirrel ·   Reeves's Muntjac ·   Reindeer ·   Rhesus Macaque ·   Right Whale ·   Rock Cavy ·   Rodrigues Fruit Bat ·   Roe Deer ·   Rufous Bettong ·   Rufous-naped Tamarin ·   Rufous Rat Kangaroo ·   Saddle-back Tamarin ·   Savanna Baboon ·   Sea Otter ·   Serotine Bat ·   Sheep (Domestic) ·   Siamang ·   Sika Deer ·   Slender Tree Shrew ·   Sooty Mangabey ·   Sperm Whale ·   Spinifex Hopping Mouse ·   Spinner Dolphin ·   Spotted Hyena ·   Spotted Seal ·   Squirrel Monkey ·   Striped Dolphin ·   Stuart's Marsupial Mouse ·   Stumptail Macaque ·   Swamp Deer ·   Swamp Wallaby ·   Takhi ·   Talapoin ·   Tammar Wallaby ·   Tasmanian Devil ·   Tasmanian Rat Kangaroo ·   Thinhorn Sheep ·   Thomson's Gazelle ·   Tiger ·   Tonkean Macaque ·   Tucuxi ·   Urial ·   Vampire Bat ·   Verreaux's Sifaka ·   Vervet ·   Vicuna ·   Walrus ·   Wapiti ·   Warthog ·   Waterbuck ·   Water Buffalo ·   Weeper Capuchin ·   Western Grey Kangaroo ·   West Indian Manatee ·   Whiptail Wallaby ·   White-faced Capuchin ·   White-fronted Capuchin ·   White-handed Gibbon ·   White-lipped Peccary ·   White-tailed Deer ·   Wild Cavy ·   Wild Goat ·   Wisent ·   Yellow-footed Rock Wallaby ·   Yellow-toothed Cavy