Sunday, May 19, 2013

Shrinking Alligator Penises: Using Wildlife Models to Study How Chemical Contaminants May Affect Human Reproductive Systems (Guest Post)



Erin on the side of a river somewhere
 in western NC, hard at work study obviously.
Erin Abernethy is a Master’s student in the Odum School of Ecology at the University of Georgia, where she is studying scavenging ecology in Hawaii. Before coming to Athens, Erin lived in North Carolina earning her BS in Biology at Appalachian State. For that degree, she was investigating potential fragmentation in freshwater mussel populations around small mill dams. She then worked in eastern NC chasing down Spotted Turtles, Clemmys guttata, for Clemson University, while also learning to garden and bake delicious grape hull pies from her Great Aunt Marie.

Penises are shrinking. In the male American Alligators, Alligator mississipiensis, of Florida’s Lake Apopka, that is. The culprit? Endocrine disruptors. Endocrine disruptors are chemicals that interfere with the endocrine system (the system of glands that secretes hormones directly into the bloodstream) and cause adverse developmental, reproductive, neurological, and immune effects. Well-known endocrine disruptors include birth control pills, BPA (ever heard of BPA-free plastic water bottles?) and DDT (dichlorodiphenyltrichloroethane), a pesticide that is now banned in the USA. I first heard about endocrine disruptors while watching Fooling with Nature, a PBS documentary that introduced me to Lake Apopka and the leading scientist on the project, Dr. Lou Guillette.

Dr. Guillette with an American Alligator.
Hope that duct tape holds!
Dr. Guillette is intrigued by reproduction. He completed his Master’s and Ph.D. work on the reproductive evolution of Yarrow’s Spiny Lizard, Sceloporus jarrovi, and the Mexican Lizard, S. aeneus, respectively. In 1985, he was employed by the University of Florida as an assistant professor in the Zoology Department and began to study American Alligators in Lake Apopka, which is the third largest lake in Florida and is located in central Florida. He says that he began working on Lake Apopka to study the general health and reproductive biology of the alligators. At the time, Florida Fish and Game Commission scientists were concerned that the population of alligators at this lake was not rebounding from previous population declines despite restrictions on hunting them. Dr. Guillette began to notice abnormalities in the alligator eggs and juveniles and started looking for the cause. He discovered abnormal hormonal levels in both male and female alligators and wondered if environmental contaminants could be causing these abnormalities. He hypothesized that Lake Apopka was contaminated with endocrine disrupting chemicals that were adversely affecting the reproductive physiology of these alligators. 

Since developing that initial hypothesis, Dr. Guillette completed many studies on the alligators in Lake Apopka, such as the one published in 1996 entitled “Reduction in Penis Size and Plasma Testosterone Concentrations in Juvenile Alligators Living in a Contaminated Environment.” In this study the penis sizes of two populations of alligators were compared. One population was from Lake Apopka, which had been shown to be contaminated with agricultural and municipal chemicals such as DDT, dicofol (a pesticide), and sulfuric acid. The other population was living in the relatively secluded Lake Woodruff located 65 km (40 miles) away on a National Wildlife Refuge.

Hand grabbing gators at night.
Sounds like fun!
So how do you conduct a survey on penis size of alligators? First you have to catch them! To catch juvenile alligators, which are generally less than 1.2 m (4 feet) long, researchers pile into a small boat that is relatively low on the water and motor out to their study sites while the sun is setting. Once the sun sets, they can use a spotlight to find the “eye shines” of the alligators. Alligator eyes reflect light much like the eyes of a deer in your headlights. Once they have their sights set on an alligator, they motor over to it with one brave soul at the front of the boat ready to HAND-grab that little gator. Can you imagine yourself belly down, hanging halfway off the front of a tiny boat, in the middle of the night, getting ready to stick your arm into dark black water in order to grab a baby alligator? One might wonder, “Where’s Mama?” 

By applying gentle pressure, the penis, technically referred to as the cliterophallic structure, on juvenile male alligators can be pushed out of the cloaca. The cloaca is the opening on an animal’s underside through which all products of the intestinal, reproductive, and urinary tracts exit the body. It’s also the place you want to look to see if you’ve got a male or female alligator. Once the penis is fully extended, its length and width are measured. 
Alligator penis diagram with
relevant measurements displayed.


        When the sizes of penises were compared between lakes, alligators in Lake Apopka had on average 24% smaller penises than alligators in Lake Woodruff. When the time came for these juveniles to reproduce, this significant reduction in penis size made it difficult to mate and certainly didn’t impress the lady alligators.

This study showed that male alligators in Lake Apopka, which is contaminated with endocrine disruptors, were significantly different than alligators from a lake that had relatively little pollution. In order to help determine the physiological drivers, in other words the chemical pathways in the body that shape these physical differences, behind this reduction in penis size, Dr. Guillette also looked at plasma testosterone concentrations. Plasma testosterone is responsible for the formation and development of male external genitalia. He discovered that juvenile alligators in Lake Apopka had 70% lower concentrations of plasma testosterone than those at Lake Woodruff. Abnormal hormone levels like these are associated with decreased sperm counts and reduced fertility. This can be disastrous for maintaining healthy wildlife populations. The results of this study inspired Dr. Guillette to continue to look at the physiological effects of endocrine disruptors on reproductive systems.

Over the past couple of decades, Dr. Guillette and many other scientists have described the physiological effects of endocrine disruptors on many groups of wildlife. In male fish and amphibians, these effects include not only a reduction in testosterone but an increase in estrogen (female sex hormone) production and even the production of eggs, egg yolk, and ovaries (yes, in males!). In both sexes of rats, an increase in reproductive system cancers (prostate and breast) and immune system failure was seen when animals were exposed to endocrine disrupting chemicals. Rats, fish, tadpoles, and salamanders exposed to atrazine (an endocrine disrupting pesticide) experienced neurological effects such as damaged brain cells that resulted in decreased cognition, hyperactivity, and erratic behavior. So what do these harmful effects of endocrine disrupters on animals mean for humans?

Dr. Guillette says that he is currently focused on answering that question. He has moved away from simply studying the reproductive physiology of the alligator, and now uses the alligator as a wildlife model for understanding the potential effects of endocrine disruptors on human reproductive systems and embryos. He is now working at the Medical University of South Carolina as a Professor of Obstetrics and Gynecology! He appreciates this unique opportunity to meld his wildlife research with that of medical researchers. Some of his current research is delving into the different routes of exposure to endocrine disruptors and how these influence embryonic development. There are over 1,000 chemicals out there that are endocrine disruptors, and we are all coming into contact with them every day through our drinking water and many consumer products, plastic toys, cosmetics, cleaning products. How are they affecting our bodies and our children? We don’t know, but that is what Dr. Guillette is looking into.

Dr. Guillette believes that if baby alligators are not healthy, our human babies won’t be healthy either. As the evidence for this hypothesis grows (see also Dr. Tyrone Hayes’ website for more information on the effects of endocrine disruptors on humans), scientists must inform the public so that actions can be taken. Public opinion is the most powerful driver for policy change in this country and only a loud public outcry will alter how chemicals are produced, studied, and regulated. USA companies are putting over 500 new chemicals a year on the market without thoroughly examining their potential side effects, which should take years to do.

What actions can you take? Be aware of what you are consuming and coming into contact with. Could it be an endocrine disruptor? Do some research and don’t be intimidated by scientific articles. Many scientists are making an effort to write their conclusions so that they are comprehensible to a wider audience. Write to your representatives and legislators and become involved in local action groups to increase studies and restrictions on new and old chemicals that are being used in consumer products and agriculture without being fully investigated for potentially harmful side effects. Just as in alligators, these pollutants may affect our young. It is critical for the health of our children that we become aware of and regulate what we are putting into the environment and our bodies.


For further information about endocrine disruptors, please refer to these websites and/or scientific articles:


Guillette Jr., L., Pickford, D., Crain, D., Rooney, A., & Percival, H. (1996). Reduction in Penis Size and Plasma Testosterone Concentrations in Juvenile Alligators Living in a Contaminated Environment General and Comparative Endocrinology, 101 (1), 32-42 DOI: 10.1006/gcen.1996.0005

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