BAKER, P.J.*; COSTANZO, J.P.; IVERSON, J.B.; LEE JR., R.E.; Miami University; Miami University; Earlham College; Miami University: Adaptations to terrestrial hibernation of hatchling northern map turtles (Graptemys geographica)

Field observations and laboratory experiments were conducted on hatchlings of the northern map turtle (Graptemys geographica), a species that commonly overwinters within the natal nest in the northern parts of its range. During this 3 year study, hatchlings from 19 of 20 natural nests emerged in spring rather than fall. The minimum winter temperature experienced in the nest was �5.4�C, yet despite frequent and sustained potential freezing events, winter mortality was limited to a single hatchling. In the laboratory, we assessed the cold-hardiness of G. geographica by evaluating a suite of physiological adaptations that contributes to winter survivorship: desiccation resistance, tolerance of somatic freezing, intrinsic supercooling capacity, and resistance to inoculation by environmental ice nuclei. In addition, we examined the physiological effects of deep supercooling and hypoxia exposure. Hatchlings had relatively low rates of evaporative water loss (2.0 mg g^-1 d ^-1), supercooled deeply (to -14.8�C) and exhibited a remarkably high resistance to inoculation by external ice nuclei. However the hatchlings were intolerant of freezing at -2.5�C for 24 h, which suggests that this species survives severe winter conditions by remaining unfrozen in a state of supercooling. This research was supported by the National Science Foundation (IBN 98017087).