Thermoregulation When the Growing Season Is Short: Sex-Biased Basking Patterns in a Northern Population of Painted Turtles (Chrysemys picta)

In reptiles, thermoregulation is important because it alters the rate of many physiological processes. Thermoregulation may be especially important to reproductive females that inhabit regions where the growing season is short, because the amount of thermal energy experienced during the season may limit the amount of energy devoted to egg production. We studied basking behavior of Painted Turtles (Chrysemys picta) in Algonquin Park, Ontario, during the period of follicular recrudescence, a time of year when females allocate energy to developing follicles. Based on the notion that females bask (in part) to increase the amount of energy they allocate to developing follicles, we tested whether basking duration was greater in females than in males. Between 14 and 21 August 2003, we found that females basked longer than males on three of seven days, but males never basked significantly longer than females. Within sex, male but not female body size was positively related to basking duration. Our study suggests that the energetic demands of egg production result in an increased basking duration for females in this northern population. Males may bask to reach a certain temperature then return to water because of potential mating opportunities. Future studies should combine body temperature measurements with behavioral observations to elucidate further the reasons for sex-biased basking.