SEARS, Michael W; ANGILLETTA, Michael J; PORTER, Warren P; Indiana State University; Indiana State University; University of Wisconsin-Madison: Getting back to nature: ecological influences on patterns of growth and body size in squamate reptiles

Recently, there has been much interest in geographic patterns of growth and body size in all taxonomic groups. Though many, if not most, organisms follow Bergmann’s rule�larger body size in cooler environments�squamate reptiles are notable for exhibiting the reverse pattern. What makes squamates such exceptional organisms? Why have the life histories of squamates not evolved in the same manner as so many other organisms? The answer is likely to be found in thermoregulatory behavior. Many squamates regulate their body temperatures within a narrow range and are only active when they can achieve those temperatures. To complicate matters, squamates must balance the need to thermoregulate with the need to forage and avoid predators. Only when squamates can’t meet their energetic demands through modifications in thermoregulatory behavior should we expect the thermal sensitivity of growth rates to evolve. To date, geographic patterns of body size have been examined in the context of latitudinal or elevational gradients, with the expectation that cooler environments limit growth more than warmer environments. In reality, warmer environments may also be limiting when temperatures exceed tolerable limits. We will re-examine geographic patterns of growth and body size in relation to the potential times available for activity in a particular environment. We will discuss these patterns in the context of a broader theoretical framework that incorporates tradeoffs associated with behavioral and physiological adaptation to the thermal environment.