Effects of post-hatching maintenance temperature on desert tortoise (Gopherus agassizii) shell morphology and thermoregulatory behavior

Effects of post-hatching maintenance temperature on growth, morphology, and behavioral thermoregulation were studied in the desert tortoise (Gopherus agassizii). Tortoises were held at one of three temperatures (19, 28, 37 C) during the four months following hatching, then placed into a control temperature of 28 C. Body mass, maximum plastron width, height, and length ratios were determined monthly for the following year. Nine months post-hatching, cloacal and shell temperatures were determined while animals were allowed to behaviorally regulate their temperature in a thermal gradient ranging from 23-45 C. Animals held at 37 C had a greater surface area-to-volume ratio (flat morphology) than animals maintained at 19 or 28 C (round morphology). These morphological changes were correlated with thermoregulatory behavior. Animals with a greater surface area-to-volume ratio (37 C) had a lower cycle frequency (movement between minimum and maximum temperatures) and higher mean core temperature than 19 and 28 C animals. These experiments indicate the existence of a window during juvenile development in which temperature will influence morphological and behavioral characteristics.