(757.21) Do crocodilians have an air-conditioning unit in their skulls? Experimental test of purported thermoregulatory function of the dorsal temporal fenestrae in the American alligator

Poster Board Number: E470

Breanna Alexis Ramirez (California State University), Sara Sandoval (California State University), Jon Sparks (California State University), Ruth Elsey (Louisiana Department of Wildlife and Fisheries), Tomasz Owerkowicz (California State University)

The classic view of dorsal temporal fenestrae (DTFs) in diapsids posits that they provide attachment sites for jaw adductor muscles. A recent hypothesis suggested that DTFs in archosaurs may play a role in selective brain thermoregulation, but did not provide supporting experimental data. We tested this hypothesis in two years-old juveniles of the American alligator. We used chronically implanted thermocouples to monitor brain (Tb) and core (Tc) temperatures in constrained but unanaesthetised animals during acute heat exposure. Animals were first equilibrated to either 15°C (n=9, body mass range 200-563 g) or 30°C (n=6, body mass range 173-362 g), and then exposed to a radiant heat source (a 75W incandescent light bulb suspended 20cm above the animal). As experimental treatment, we used insulating covers (custom-made of adhesive foam tape and aluminium foil) to obscure either the DTFs or a corresponding skull surface in subsequent trials. We expected that obscuring the DTF (as opposed to covering the skull roof) would result in Tb rising more slowly in animals at 15°C (i.e., interfering with selective brain warming), and would result in Tb rising faster in animals at 30°C (i.e., interfering with selective brain cooling). We found no statistically significant differences in the rate of brain warming between DTF-covered vs. skull-covered treatments in animals at either 15°C (0.541°C/min vs. 0.683°C/min) or 30°C (0.356°C/min vs. 0.358°C/min). Our results suggest that DTFs, at least in small (lt;1 kg) alligators, do not function as thermal windows for heat exchange with the environment to afford them selective brain temperature control. However, given that the DTF surface area scales with positive allometry on brain mass (Mb^1.25) in the American alligator, further experiments are needed to determine whether DTFs acquire a thermoregulatory function in larger crocodilians.

Support or Funding Information

Supported by the Summer Undergraduate Research Programme via the Office of Student Research, CSUSB.