Thermoregulatory Behavior in Reptile and Bird Embryos

As we have learned in class, thermoregulation is an extremely important behavior that allows herps to survive in different environments, and certain herps (like turtles) have the ability to thermoregulate even before hatching from their eggs. Studies have shown that embryonic thermoregulation is very similar to post-hatching thermoregulation, but a lot about this behavior still remains unknown. The ability for an embryo to thermoregulate is mostly dependent on the thermal gradient within the egg and the size of the egg, so researchers have asked the question: is a similar embryonic thermoregulation mechanism used in some reptiles used across different species of reptiles and birds?

In the article "Thermoregulatory Behavior Is Widespread in the Embryos of Reptiles and Birds," the authors conducted an experiment to test this hypothesis. In order to set up the experiment, the authors used the embryos of two species of lizards, three snakes, two turtles, one crocodile, and four birds. After the eggs were collected, they were incubated individually and then randomly assigned to a treatment group (control, warm, or hot). The results of this experiment showed that the lizard embryos did not move inside their eggs, but the embryos of snakes, turtles, alligators, and birds all moved inside of their eggs closer towards the heat source. This study shows that certain reptile and bird embryos have the ability to reposition themselves inside the egg to seek sources of heat and/or remove themselves from dangerously hot temperatures.

While this is study adds to the already known literature on herps and thermoregulation, this research also highlights the evolution of reptilia and their common ancestors. On the phylogenies that we have studied in class, the group "lizards" is listed multiple times, and in this study, the two species of lizards were the only herps that did not perform embryonic thermoregulation. This information suggests that this behavioral mechanism was somehow lost in certain lizard species but retained in other members of the group reptilia.


Article Review:
Li, Teng, Bo Zhao, Yong-Kang Zhou, Rui Hu, and Wei-Guo Du. "Thermoregulatory Behavior Is Widespread in the Embryos of Reptiles and Birds." The American Naturalist. 2014: 445-451. (http://www.jstor.org/stable/10.1086/675065)