Journal of Thermal Biology 31 (2006) 400–405 Response of hatchling wood turtles (Glyptemys insculpta) to an aquatic thermal gradient Jeff Tamplin à Department of Biology, University of Northern Iowa, Cedar Falls, Iowa 50614, USA Received 23 September 2005; accepted 19 January 2006 Abstract Effective thermoregulation and the ability to select preferred temperature is an important factor influencing fitness in hatchling and juvenile turtles. Six-month-old Glyptemys insculpta acclimated to 20 1C selected the warmest temperature available and avoided the coldest temperature available in a gradient of 12–27 1C. Turtles visited fewer chambers and switched chambers in the gradient tank less frequently when the gradient was present than during control tests. Mean selection of chambers differed between control and gradient tests across all temperatures except at 21 1C, the temperature closest to the acclimation and control temperature (20 1C). r 2006 Elsevier Ltd. All rights reserved. Keywords: Thermoregulation; Selected temperature; Thermal preference; Temperature gradient; Reptile; Turtle; Glyptemys; Emydid turtles; Juvenile turtles 1. Introduction Environmental temperature selection is a primary factor influencing the survivorship, growth, reproduction, and physiological performance of aquatic and semiaquatic turtles (Brooks et al., 1991; Janzen and Paukstis, 1991; Ewert et al., 1994; O’Steen, 1998; Rhen and Lang, 1999; Sajwaj and Lang, 2000). Maintaining body temperature within an auspicious range enhances metabolic function, nutrient digestion, and immunological protection in turtles (Parmenter, 1981; Huey, 1982; Hammond et al., 1988; Knight et al., 1990; Rome et al., 1992); however, other factors affecting microhabitat selection, such as access to mates or the need to remain cryptic, may influence thermal preference in some turtles (Graham and Hutchison, 1979; Spotila et al., 1984; Galbraith et al., 1987; Brown et al., 1990; Nebeker and Bury, 2001). Many freshwater turtles thermoregulate with aerial or aquatic basking, and the ability to balance foraging, social interaction, and predator avoidance with selecting preferred thermal niches may be an important behavioral adaptation influencing fitness. Selection of elevated temperatures in laboratory-based aquatic thermal gradients occurs in adult Chrysemys picta (Lefevre and Brooks, 1995), Chelydra serpentina (Schuett and Gatten, 1980), and Trachemys scripta (Crawford et al., 1983; Jarling et al., 1989) and in hatchling and juvenile Chelydra serpentina (Williamson et al., 1989; O’Steen, 1998; Bury et al., 2000), Apalone mutica (Nebeker and Bury, 2001), and two emydid species (Pseudemys nelsoni, Nebeker and Bury, 2000; and Trachemys scripta, Jarling et al., 1984, 1989; Bury et al., 2000). Hatchling and yearling turtles placed in aquatic thermal gradients typically select warm (27–33 1C) temperatures within a narrow range. While these studies suggest that juvenile turtles actively thermoregulate, these values may be higher than observed body temperatures of adult turtles in field studies (Ernst, 1986; Brown et al., 1990; Sajwaj and Lang, 2000). Data on the thermal preference and basking behavior of wild juveniles are limited to reports by Janzen et al. (1992) and Lindeman (1993). North American wood turtles (Emydidae: Glyptemys insculpta) are semiaquatic, diurnal turtles that show seasonal shifts in activity and habitat usage; wood turtles ARTICLE IN PRESS www.elsevier.com/locate/jtherbio 0306-4565/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jtherbio.2006.01.010 à Department of Biology, University of Northern Iowa, 1227 W 27th Street, Cedar Falls, Iowa 50614-0421 USA. Tel.: +1 319 273 2327; fax: +1 319 273 7125. E-mail address: jeff.tamplin@uni.edu.