Stable Isotopes and the Ecology and Physiology of Reptiles

When animals don’t have enough food, they have to “choose” between “spending” their limited energy on themselves or on their offspring. Biologists think that reptiles can make this choice quickly in response to different environments. But, it can be hard to study these choices because it is hard to convert between, for example, the number of eggs laid and the speed of healing a wound. By using stable isotope chemistry, we can collect more detailed and comparable information about how lizards and other animals spend their limited resources than with any other method. For example, lizards in the wild have similar stable isotope signatures to nearby plants and insects, because their bodies are built out of these foods. In the lab, the stable isotope signatures of lizard “pee” (uric acid) change in predictable ways when they are hungry. We could essentially measure how hungry a wild lizard is by looking at the stable isotope signatures of its uric acid. We can also use a stable isotope “spike” to track where resources go within a lizard’s body. Because protein from food is used for both healing wounds and creating egg yolk, we can measure which of these is a greater priority for lizards by examining the amount of our stable isotope spike that ends up in both places. I found that lizards make different choices under different circumstances; in particular, their stage of pregnancy had a strong effect on how much protein they put into their eggs. This technique could be used on any animal, isn’t very expensive, and could help us learn a lot more about exactly how our bodies, and those of other animals, work