Intraspecific differences in thermal tolerance of the diamondback watersnake (Nerodia rhombifer): effects of ontogeny, latitude, and sex
Christopher T. Winne*, Michael B. Keck
Stephen F. Austin State University, Department of Biology, Box 13003
SF A Station, Nacogdoches, TX 75962, USA
Received 27 August 2004; received in revised form 16 November 2004; accepted 16 November 2004
Abstract
Ontogenetic shifts in microhabitat use are widespread among taxa and can
result in drastic shifts in thermal habitat among age classes. Likewise,
geographic variation in climate along latitudinal gradients can cause
differences in thermal environments among populations of a species. Using
a common garden design, we examined four populations of a single species
of semi-aquatic snake, Nerodia rhombifer, to determine whether
ontogenetic shifts in habitat use (and/or body size) and latitudinal differences
in ambient temperature have resulted in evolutionary changes in thermal
tolerance. We found ontogenetic differences in thermal tolerance for all
populations, with neonates tolerating temperatures 2 °C higher than
adults, a pattern that is consistent with ontogenetic shifts in body size
and microhabitat use in this species. There were differences in thermal
tolerance among latitudes in neonates, suggesting genetic differences
among populations, but adults showed no latitudinal differences. In combination,
the increased thermal tolerance of neonates and the age-specific response
to latitude suggest individuals may be most sensitive to selection on
thermal tolerance as neonates. Although latitudinal differences exist
in neonates, their tolerances were not ranked according to latitude, suggesting
the effects of some other local factor (e.g., microclimate) may be important.
Lastly, among neonates, females tolerate higher temperatures than males.
Published by Elsevier Inc.
Keywords: Age; Critical thermal maximum; CTMax; Genetic variation;
Geographic variation; Heat tolerance; Latitude; Natricinae; Temperature;
Thermal physiology
SREL Reprint #2817
Winne, C. T. and M. B. Keck. 2005. Intraspecific differences in thermal tolerance of the diamondback watersnake (Nerodia rhombifer): effects of ontogeny, latitude, and sex. Comparative Biochemistry and Physiology, Part A 140:141-149.
