CUR - The Council on Undergraduate Research

Nesting ecology of the leatherback sea turtle, Dermochelys coriacea

Kathryn Burda, Laura Romero, and Nicole Valenzuela, Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011

Many turtles and other reptiles produce temperature-dependent characteristics in embryos, and sea turtles are no exception. Here we review salient observations accumulated over 35 years of research on Dermochelys coriacea to discern how nest environment influences its sex determination, development, and basic biology. Environmental temperature during a critical period of embryogenesis determines whether an egg develops as male or female. Sex ratios are diagnosed by examining the gonads of some hatchlings, whereas others are released into the ocean. Most studies report a pivotal temperature of 29.5°C (which produces 1:1 sex ratios), whereas the transitional range of temperature (TRT, which produces mixed sex ratios) vary by populations (<1°C in some and >3°C in others). Incubation temperatures higher than the TRT produce 100% females, and lower values produce 100% males. The recorded incubation temperature ranges ultimately depend on the experimental treatment type used in various studies. Treatments reported include natural nests, hatcheries, styrofoam boxes, and incubators or temperature-controlled ovens. Some treatments were designed to mimic natural nest conditions in an attempt to avoid deviating largely from the environmental characteristics of the original female nesting site. The placement of each nest on the beach can also affect the temperature range that a particular nest experiences due to factors such as how much sun or shade the sand receives at a particular area, and how far of a distance the nest is to high tide. Internal factors can also regulate sand temperature. These include nest depth, egg position within the egg chamber, and metabolic heat generated by developing embryos. Other external large-scale factors such as annual and seasonal differences in the climate affect the sand temperature to the greatest extent. Thus, contemporary climate change is predicted to have detrimental feminization effects on sea turtle populations that could pose a risk for their survival.

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