Behavioral responses of hatchling painted turtles (Chrysemys picta ) and snapping turtles (Chelydra serpentina ) at subzero temperatures Jon P. Costanzo*, Jacqueline D. Litzgus, Richard E. Lee Jr Department of Zoology, Miami University, Oxford, OH 45056, USA Received 10 November 1998; received in revised form 6 January 1999; accepted 20 January 1999 Abstract We monitored behavioral responses of cold-acclimated hatchling painted turtles (Chrysemys picta ) indigenous to Nebraska and hatchling snapping turtles (Chelydra serpentina ) indigenous to Nebraska and Arkansas during cooling (0.18C/min) to temperatures as low as À198C. All turtles made exploratory movements during cooling and locomotion occurred at temperatures as low as À2 to À48C, but C. picta maintained relatively higher levels of locomotor activity than C. serpentina, and no dierences in motility occurred between northern and southern groups of C. serpentina. Slow movements of the head and limbs were observed in supercooled hatchling C. picta at temperatures as low as À108C, whereas at about À58C, C. serpentina exhibited an increase in spontaneous motor activity followed by muscle contracture, immobility, and spontaneous freezing. C. picta spontaneously froze at about À168C without exhibiting cold contracture, suggesting that they are better adapted to survive exposure to extreme cold. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Behavior; Chelydra serpentina; Chrysemys picta; Cold adaptation; Locomotion; Supercooling 1. Introduction Painted turtles (Chrysemys picta ) hatch in late sum- mer but overwinter within the nest chamber, about 10 cm below the ground surface (Gibbons and Nelson, 1978). In areas where snow cover persists, nest tem- peratures rarely fall below freezing (Breitenbach et al., 1984). However, in cold regions where snow cover is sparse or transient, hatchlings are commonly exposed to temperatures below the equilibrium freezing point of their tissues (about À0.68C), and occasionally to temperatures <À108C. Most of these chilling episodes are brief, lasting from several hours to a few days, although they may last a week or more and turtles may be exposed to many such events over the course of winter (Costanzo et al., 1995; Packard, 1997). Lee and Costanzo (1998) reviewed the adaptations promoting survival of hatchling C. picta at subzero temperatures. Only relatively high temperatures (e.g. À48C) may be tolerated in the frozen state, although these turtles may survive exposure to markedly lower temperatures by remaining supercooled (see Packard et al., 1997). Indeed, the supercooling capacity of C. picta (to À208C) is the best known among vertebrates and rivals that of some invertebrates (Lee and Costanzo, 1998; Costanzo et al., 1999). The snapping turtle (Chelydra serpentina ) also Journal of Thermal Biology 24 (1999) 161±166 0306-4565/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0306-4565(99)00006-6 * Corresponding author. Tel: +1-513-529-3173; Fax: +1- 513-529-6900. E-mail address: costanjp@muohio.edu (J.P. Costanzo)