Physiological Correlates of Limblessness and Fossoriality in Scincid Lizards

Abstract

Field body temperature, eccritic body temperature and response to heat stress, indicate that tetrapod, surface-active skinks (Mabuya) are more thermophilic than fossorial monodactylous (Scelotes) and limbless (Acontias) ones. Resting rates of oxygen consumption for all skinks were similar to predicted values, and were temperature-dependent. The maximal rates of oxygen consumption for skinks at 33 C were similar for Mabuya, Scelotes and Typhlacontias, but lower for Acontias. The maximal rates for Mabuya and Typhlacontias were strongly temperature-dependent, whereas those for Scelotes and Acontias were independent of temperature from 15 to 33 C. Such temperature-independence of activity metabolism would be of adaptive significance to these fossorial, predatory skinks which are unable to thermoregulate behaviorally. Rates of evaporative water loss increased with ambient temperature, and with activity. The desert species (Typhlacontias) had the lowest rate of water loss (0.02 mg cm-2 h-1) whereas the limbless, mesic Acontias had the highest rate (0.13 mg cm-2 h-1) at 23 C. All species sustained similar weight losses at dehydrational death (30-35% initial weight loss) but the number of days to dehydrational death varied markedly, from 60 days for Mabuya, 14 for Scelotes and 8 for Acontias. These differences reflect a) interspecific variation in minimum water loss rates, and b) increased rates of water loss during dehydration likely reflecting elevated activity and increased permeability of the skin to water for Acontias and Scelotes.