PETERSON, C.C.*; LIGON, D.B.; The College of New Jersey; Oklahoma State University: Metabolic depression in estivating mud turtles

Some animals survive periods of adversely dry and/or hot climatic conditions through terrestrial dormancy, termed estivation. Estivating animals should benefit from conservation of energy, but unlike hibernators, estivating ectotherms cannot rely on the acute effects of low body temperatures to reduce metabolic costs of maintenance. Thus, ectotherms have been predicted to exhibit metabolic depression (MD, programmed decrease in metabolic rate) during estivation, and MD has been demonstrated in estivating insects, snails, lungfish, and anurans. Several species of chelonians estivate, but evidence for MD in turtles is equivocal. In our previous studies of mud turtles (Kinosternon spp.), metabolic rates measured following a period of enforced estivation were paradoxically higher than before; estivating turtles were apparently sensitive to disturbance. The few published demonstrations of MD in other estivating chelonians are potentially confounded by uncontrolled effects of starvation or seasonal variation. In this study we measured oxygen consumption in yellow mud turtles (K. flavescens) estivating in the laboratory without disturbance, and compared them to a control group that was fully hydrated and active but fasted. Considering all data, decreases in whole-animal metabolic rates over 70 days were modest (10-15%) and similar for both groups. However, turtles in the “estivation” group were highly variable in behavior, and three individuals that burrowed and remained dormant showed larger, continuous decreases in metabolic rate (30-45%), whereas the largest decrease among hydrated controls was 22%. We conclude that estivating mud turtles can, in fact, exhibit MD, but the phenomenon is difficult to study in the laboratory. Issues of repeatability and correction for body size also will be discussed.