Geographic variation in thermal sensitivity of jumping performance in the frog Limnodynastes peronii.

Abstract

I compared the thermal sensitivity of jumping performance of five populations of the striped marsh frog (Limnodynastes peronii) over a wide geographic range extending from the cool-temperate south to the tropical north of Australia. Maximum jumping performance of adult L. peronii was assessed for each population at eight temperatures between 5 degrees C and 32 degrees C using a custom-designed force platform. From force recordings for each individual jump, maximum jumping force (F(max)) and acceleration (A(max)) and maximum power output (P(max)), take-off velocity (U(max)), jump distance (D(J)) and contact time on the platform (T(C)) were calculated. The body mass of adult L. peronii varied over their geographic range, from approximately 5 g for the lowland tropical population to more than 22 g for the cool-temperate populations. The thermal sensitivity of jumping performance varied over their geographic range, with the populations from the cooler climates generally performing better than those from the warmer climate populations at the cooler temperatures, and vice versa at the higher temperatures. However, not all parameters of jumping performance underwent parallel changes in thermal sensitivity amongst the populations of L. peronii. Only minor differences in the shape of the thermal sensitivity curves for F(max) and A(max) were detected amongst the populations, while the thermal sensitivities of U(max), D(J) and P(max) all displayed considerable variation amongst the populations. The optimal temperatures for U(max), D(J) and P(max) were generally lower in the cool-temperate populations than in the tropical populations of L. peronii. To determine whether this geographic variation was due to genetic variation, or merely reflected phenotypic plasticity, I also compared the thermal sensitivity of jumping performance between metamorph L. peronii from two different populations raised under identical conditions in the laboratory. The maximum jumping distance of the metamorph L. peronii was assessed at seven temperatures between 8 degress C and 35 degrees C for the two latitudinally extreme populations (i.e. lowland tropical Proserpine and cool-temperate Gippsland populations). Like adult L. peronii, the metamorphs from the cool-temperate population jumped further than those from the lowland tropical population at the lower temperatures, although no differences were detected at the higher temperatures. Thus, geographic variation in thermal sensitivity of jumping performance in L. peronii probably has a genetic component, and the different populations appear to have undergone genetic adaptation of their thermal sensitivity to the varied thermal environments.