Environmental harshness shapes life-history variation in an Australian temporary pool breeding frog: a skeletochronological approach

For many amphibians, high temperatures and limited precipitation are crucial habitat characteristics that limit species ranges and modulate life-history characteristics. Although knowledge of the ability of amphibians to cope with such environmental harshness is particularly relevant in the light of ongoing environmental change, relatively little is known about natural variation in age, maturation and associated life-history traits across species' ranges. We used the analysis of growth rings in bones to investigate the link between environmental harshness and life-history traits, including age and body size distribution, in specimens from 20 populations of the Australian bleating froglet, Crinia pseudinsignifera. Despite the short lifespan of the species, bone slides revealed geographic variation in average age, body size and reproductive investment linked to variation in temperature and rainfall. We found no difference in age at maturation in different climatic harshness regimes. Frogs from harsher environments invested less in their first reproductive event but grew older than their counterparts in more benign environments, thereby allowing for more reproductive events and buffering them against the increased chance of reproductive failure in the harsher environments. For individual frogs, climatic harshness experienced during an individual's life promoted larger body size. Overall, these results illustrate how bone structure analyses from preserved specimens allow both the testing of ecogeographic hypotheses and the assessment of the adaptive potential of species in the light of environmental change.