Seasonal effects on body temperature of the endangered grassland earless dragon, Tympanocryptis pinguicolla, from populations at two elevations

摘要

The endangered grassland earless dragon, Tympanocryptis pinguicolla, is present in two geographic locations in Australia: the Australian Capital Territory and adjacent New South Wales (NSW) near Canberra (similar to 580m above sea level) and Monaro Plains, NSW, near Cooma (similar to 950m above sea level). The lizards live in native grassland, an endangered ecological community, and although the population ecology of the animal has been examined, the importance of habitat for thermoregulatory patterns is unknown. We studied whether lizards from the two locations differ in their seasonal patterns of thermoregulation by measuring skin and chest temperatures using both radio-telemetry and temperature measurement in the field, as well as thermal preferences in a laboratory thermal gradient. These results are compared with the operative temperatures (T-e) in various microhabitats in the two regions to determine to what extent lizards are thermoregulating. We demonstrate that these lizards do not maintain a constant body temperature, but allow T-b to vary between 13 and 39 degrees C when active in the field, although the grand mean for 50% basking temperatures ranged between 32 and 36 degrees C in the laboratory gradient. Temperatures in the various microhabitats can exceed 40 degrees C, but lizards appeared to avoid those temperatures by seeking shelter in either burrows or the base of grass tussocks. Lizards could choose microhabitats that would permit maintenance of body temperatures above 30 degrees C in most seasons, but did not do so. As high body temperature is not selected in field conditions for either population, other processes (e.g. predation) may be more important for determining T-b maintenance.