A reciprocal transplant study of activity, body size, and winter survivorship in juvenile lizards from two sites at different altitude

Abstract

We examined activity rates prior to hibernation, age-adjusted body size, growth rates, and probability of recapture after spring emergence of juveniles from 2 populations of the lizard Psammodromus algirus separated by 600–700 m altitude. We captured gravid females, incubated the eggs, and released the juveniles into the wild. We used a reciprocal transplant design in a year of severe drought to distinguish between environmental and population-specific sources of variation. The levels of autumn activity differed between release sites (activity was higher at the more productive, high-elevation site) and between maternal sites of origin (at the low-elevation site, juveniles of low-elevation origin were less active than those of high-elevation origin). Although clutch mass was similar at both sites, eggs from low-elevation females were larger but fewer than those from high-elevation ones. Larger juveniles and those from high-elevation clutches had higher survival rates. The juveniles recaptured in autumn at the low-elevation site were smaller as neonates than those that were not recaptured until next spring. Our results suggest that the scarcity of prey at the low-elevation site is a selective pressure resulting in limitation of activity, given the increased energy expenditure and risk of predation incurred by active lizards. Thus, at the low-elevation site inactivity would be advantageous for most juveniles, and only the smaller ones would have to remain active frequently enough to accumulate sufficient reserves prior to hibernation. This is consistent with the selective advantage of large eggs (and small clutches) at the low-elevation site.