Geographic and annual variation in life-history traits in a temperate zone Australian skink

Life-history theory seeks to explain patterns of variation between species or populations of the same species. Studies of squamates in general, and lizards in particular, have assumed a prominent place in the understanding of such variation. However, to date, there have been surprisingly few studies of the Scincidae, a major squamate taxon. We investigated geographic and interannual variation in life-history traits in two populations of the Tasmanian spotted snow skink, Niveoscincus ocellatus, living at the climatic extremes of the species' distribution. Within each population, there were no interannual or intersexual differences in adult body size. However, mature individuals from a cold subalpine/alpine site were significantly larger at maturity, and had a larger maximum body size than mature individuals from a warmer coastal site. These findings are consistent with current predictions of the proximate effect of the thermal environment on lizard growth and size and age at maturity. In both populations, female fecundity was size-related. Litter size did not vary between years at either site, but, contrary to expectations, females from the cold site had the same or higher size-adjusted reproductive output as those from the warm coastal site. We suggest that resource availability is high at both sites and that a high reproductive output by females from the cold site does not confer a significantly higher survival risk than a lower reproductive commitment. Offspring were largest at the cold site, which is consistent with variation in offspring size of other widespread species and may occur because of strong selective pressures on early survival and growth at the cold site.