Critical Thermal Maximum Temperatures in Australian Scincid Lizards: Their Ecological and Evolutionary Significance.

Abstract

The critical thermal maximum temperature (CTMAX) has now been determined for representatives of 16 of the 21 genera of scincid lizards in Australia. Taxa from the warm interior of the country generally have a mean CTMAX greater than 39.5°C regardless of their behaviour or habitat. Taxa from the cooler periphery of the continent fall into two groups based on their behaviour and habitat: diurnal, surface- dwelling forms generally have a mean CTMAX above 39.5°C whereas crepuscular to nocturnal. or cryptozoic to fossorial forms, have a mean CTMAX below 39.5°C. The skinks of the interior probably evolved from ancestors occupying habitats most similar to ones now occurring on the periphery. In these more equable habitats. diurnal surface-dwelling forms, with their high CTMAX, would have been preadapted to invade the habitats of the interior, whereas crepuscular to nocturnal. or cryptozoic to fossorial forms, with their low CTMAX, may have had to overcome a thermal barrier to enter these habitats. This may account in part for the paucity of crepuscular to nocturnal or cryptozoic to fossorial skink lineages in the interior. Unlike most other lizard families, most skinks do not pant when heat stressed. The reasons for this are unknown.