THE INFLUENCE OF FEMALE REPRODUCTIVE STATUS ON THERMOREGULATION IN A VIVIPAROUS SNAKE, CROTALUS-VIRIDIS

The interaction between thermoregulation and reproductive status in females of viviparous reptiles is considered strong. However, field studies comparing thermoregulation between gravid and nongravid females in the same population have been rare and no general patterns have emerged. In this study we compared thermoregulation of female western rattlesnakes (Crotalus viridis) in different reproductive states using temperature-sensitive radiotelemetry. The study was conducted in an outdoor enclosure, making it possible to record body temperature (T(b)) more or less simultaneously from all of the animals. All individuals displayed a triphasic diel pattern of T(b) variation throughout the summer: T(b) rose rapidly in the morning, maintained a stable plateau in the afternoon, and declined slowly at night. During the afternoon plateau, mean T(b) of gravid and nongravid females did not differ, but those of gravid females were significantly less variable. For gravid females mean plateau T(b) increased across the season. There was no seasonal change in mean T(b) for nongravid females, but the variance of T(b) increased considerably as fall approached. Such shifts may reflect the changing costs and benefits of thermoregulation during the summer.