Ligon, D.B.*; Peterson, C.C.: Physiological Variation in Estivation among Mud Turtles (Kinosternon spp.)

Sonoran mud turtles (Kinosternon sonoriense) have long been believed to be obligately aquatic, yet recent evidence suggests that populations in the extreme eastern portion of the species’ range thrive in habitats that experience annual drying. We compared the physiological response to dry conditions of K. sonoriense from two populations: one from Arizona, in which turtles have been described as primarily aquatic, and one from New Mexico, in which extensive estivation has been documented. For comparative purposes, the responses of groups of K. flavescens (a well-documented estivator) and K. hirtipes (a highly aquatic species) were also measured. All four groups were subjected to simulated dry-season conditions in the laboratory. Resting metabolic rates and rates of evaporative water loss were measured prior to removal from water, after seven weeks of estivation, and following rehydration. Blood samples were drawn at the same intervals. Over the course of the study, Arizona K. sonoriense exhibited rates of mass loss similar to those of K. hirtipes, but that were higher than both the New Mexico K. sonoriense and K. flavescens. Differences among groups were evident in rates of evaporative water loss, resting metabolic rates, and several blood chemistry variables, including Na⁺, K⁺, and BUN. The effects of behavior on physiological response to estivation were examined.