The crocodile project explained

The American crocodile (Crocodylus acutus) is a large top predator living in diverse aquatic and terrestrial habitats, which makes it a good indicative species of general ecosystem health. Although the crocodile population in the Tempisque River (Guanacaste providence, Costa Rica) appears healthy in terms of numbers, researchers have noted a skewed sex ratio– more males than females - in the river. Normally crocodile populations have a 1:1 sex ratio, but in the Tempisque river the sex ratio is skewed towards males with a 3:1 ratio. The main factor in sex-determination for crocodiles is temperature, but whether a change in climate and temperature is the cause for the observed effect is heavily debated. You see, all sex in crocodiles is determined by temperature, and is thus not determined with the genes of the parents as in humans and other mammals. Certain temperatures will create certain sexes in the babies, no matter what. Unless there are chemicals disturbing the biological processes when the fetus is developing. My project aims to find out why there are so many males in the river and tests the possibility that pesticides might be the reason. In order to answer these bewildering questions I first had to find crocodile eggs. This was done with a colleague of mine (Ludvig Orsén) in Costa Rica between December and March in the national park of Palo Verde. From there I dissected the crocodiles and brought tissue samples back to Sweden for analysis. The tricky part of this project was to figure out what that needed to be analyzed in order to answer the question if pesticides might be the cause of the seen effect. There are many things that are happening during the development of any animal, but one process that is important is the conversion from testosterone to estrogen. Testosterone being that commonly used illegal substance used for doping of athletes (or non-athletes I suppose) who want a fast ticket to easy-muscle-building-land. One could simply refer to it as the male hormone. And estrogen is the opposite, it is the hormone that females will have in a abundance and is really the key to feminine attributes. When the body wants to produce either of these two it first makes the testosterone. If the body aims to produce estrogen, it will also produce an enzyme that functions in transforming the testosterone into estrogen. This enzyme is called aromatase and is the enzyme that I will be looking for in the crocodile eggs. Why? Because it makes sense. If there are more males than females wouldn’t it be an easy explanation to say that the females just couldn’t transform the testosterone and was kind of stuck with it in their bodies, and thus had to become male? In Costa Rica there are pesticides used that would have this effect – inhibition of aromatase, meaning that it stops working. The amount of pesticides found inside of a crocodile egg is also a great and appropriate biomarker (a measurable change due to an environmental condition) indicator of environmental contamination as the mother will transfer her burden of contaminants to the eggs8. It is possible to check the exposure to some chemicals and pesticides by looking at how much protection against it an animal has produced. So I will look for this as well in the eggs. This thesis together with a complementary thesis investigating temperatures and other ecological data within the nest might shed some light on if the skewedness in sex ratio in the American Crocodile in Costa Rica is due to endocrine disruption or a changing climate. This projcet is expected to be finished October 2015.

B.Sc Linda Eckardt

#Thecrocodileproject