The PIs will investigate physiological, ecological, and evolutionary aspects of cold hardiness in certain amphibians and reptiles. This research will use the wood frog and hatchlings of the painted turtle as models to investigate two cold-hardiness strategies employed by lower vertebrates: supercooling and freeze tolerance. Supercooled animals are in a metastable state in which the body fluid remains liquid (uncrystallized) at temperatures well below its freezing point. Freeze-tolerant animals survive exposure to subzero temperatures by tolerating the freezing of their body tissues. Studies will identify environmental and physiological factors influencing the ability of hatchling painted turtles to remain supercooled during hibernation in their nests, which lie within the frost zone. Field and laboratory studies will explore the effects of moisture on cold hardiness. A comparative study will examine the relationship between desiccation resistance and supercooling capacity in hatchlings of several species of northern turtles from diverse habitats. This work will provide insight into the physiological and morphological adaptations permitting some species of northern turtles to hibernate on land. Research in ecological physiology often considers the benefits of a particular adaptation without regard to its deleterious consequences. This project will identify "trade-offs" incurred by freeze-tolerant animals by investigating the impact of freezing and thawing on selected aspects of organismal performance. Studies of the wood frog will expand recent findings of freezing-induced impairment of locomotor performance and reproductive potential, and provide a rigorous evaluation of freeze tolerance as an adaptive, winter-survival strategy. Physiological studies, including NMR imaging of intact frogs during freezing and thawing, are aimed at identifying the underlying cause of the impairment. By integrating field and laboratory studies, this research will provide novel insights concerning adaptations that not only promote survival at subzero temperatures, but also influence the geographic distributions of some amphibians and reptiles. In addition, this work has implications for applied disciplines, such as the development of methods for cryopreserving mammalian organs and the use of cryopreserved gametes from amphibians for ex situ propagation and reintroduction programs.
