Geographic Variation in the Lower Temperature Tolerance in the Invasive Brown Anole, Anolis sagrei and the Native Green Anole, Anolis carolinensis (Sauria: Polychrotidae)

Invasive species are considered to be the second greatest threat to native biodiversity and several factors have been identified as contributing to the success of introduced species, including their initial genetic variation and the ability of populations to adapt to a new environment. Temperature has a significant impact on reptilian ecology and distribution since they ordinarily rely on external heat sources for the maintenance of body temperatures suitable for normal activity. Body temperature affects performance in these organisms given its importance for all aspects of behavior, locomotion, courtship and rates of feeding and growth. Critical thermal tolerances can, therefore, give an indication of the range of climatic conditions that can be tolerated and which may be the causal range limit in some cases. We studied the cold tolerance (Critical Thermal Minima) of female and male invasive Anolis sagrei and native Anolis carolinensis (Sauria: Polychrotidae) in four populations along a latitudinal gradient from south Florida to northern Georgia. Cold tolerance (CTMin) was measured under field conditions and after a period of acclimation to identify whether there is variation in this characteristic as latitude increases reflecting differential selection for lower temperature adaptation or phenotypic plasticity and whether there is a difference in cold tolerance between the native and invasive species. We found a geographic cline in field CTMin for both species; the lowest CTMins were exhibited by those anoles from the northern-most population (Savannah, GA). In all four populations A. carolinensis has a lower field cold CTMin than A. sagrei, and for both species, male CTMin is lower than female CTMin. However, after a period of acclimation, there were no significant differences in CTMin among populations or between sexes of either species, suggesting a notable capacity of both species to acclimate to local conditions.