Thermal sensitivity of digestion in Sceloporus consobrinus, with comments on geographic variation

Individual variation in energetics, environment, and genetics can influence population-
level processes. However, it is often assumed that locally measured thermal and bioenergetic
responses apply among broadly related species. Even closely related taxa may differ in the
thermal sensitivity of performance, which in turn influences population persistence, population
vital rates, and the ability to respond to environmental changes. The objectives of this project
were to quantify the thermal sensitivity of digestive physiology in an Sceloporus lizards, to
compare closely related, but geographically distinct, populations. Sceloporus lizards are a model
organism, as they are known to exhibit thermally dependent physiologies and are geographically
widespread. Digestive passage time, food consumption, fecal and urate production,
metabolizable energy intake (MEI), and assimilated energy (AE) were compared for Sceloporus
consobrinus in Arkansas and S. undulatus in South Carolina and New Jersey. Published data
were acquired for NJ and SC lizards, while original data were collected for S. consobrinus.
Comparisons of digestion among populations were made at 30°C, 33°C, or 36°C. Results suggest
that digestive physiology differs among populations, with S. consobrinus being more efficient at
warmer temperatures. In contrast, NJ and SC lizards had quicker passage times and lower fecal
and urate production at 30ºC in comparison to AR. The results of the current study exemplify
how closely related organisms can differ in thermal sensitivity of performance. Such data are
important for understanding how individual-level processes can vary in response to climate, with
implications for understanding variation in physiological traits across the range of Sceloporus
lizards.