Cold-Climate Adaptation in the Five-Lined Skink: A Common-Environment Experiment

Ectotherms in cold climates have unique obstacles, especially in winter. Reptiles at higher latitudes or elevations have differing strategies to survive harsher winters, but these differences (e.g. lowered metabolism and lower critical minimum temperatures) may be adaptations or the result of phenotypic plasticity that depends on environmental stimuli or an interactive effect of both. We collected five-lined skinks (Plestiodon fasciatus) from Texas and Minnesota to test for latitudinal differences in winter preparation in a common-environment experiment. We manipulated photoperiod and temperature to be either constant or decreasing, resulting in a 2x2 experiment. We asked three main questions: 1) Is there ecotypic variation between populations of lizards from different latitudes? 2) How do photoperiod and temperature independently or conjointly cue lizards to prepare for winter? 3) What variables can we measure to gauge whether lizards are preparing for winter? To determine how the lizards were preparing for winter, we measured several winter dependent variables. High-latitude lizards had greater oxygen consumption and smaller fat bodies. Lizards exposed to a decreasing photoperiod had greater oxygen consumption and lower blood glucose levels. Lizards exposed to a decreasing temperature had lower oxygen consumption, decreased food consumption, slower sprint speeds, lower critical minimum temperatures, and lower blood glucose levels. There was a significant interaction effect between photoperiod and latitude for oxygen consumption, meaning our high-latitude lizards responded more strongly to the photoperiod cue. This interaction is support for ecotypic variation between latitudes. More of our winter variables were influenced by temperature than photoperiod. Supercooling points and liver glycogen content were not affected by latitude, photoperiod, temperature, or sex. Our evidence of population differences in cold-climate traits could be proven adaptive in experiments that control for parental and developmental effects, but our data suggests adaptation in some variables