Trade-offs between burst performance and maximal exertion capacity in a wild amphibian, Xenopus tropicalis.

Trade-offs are thought to impose barriers to phenotypic diversification and may limit the evolutionary responses of organisms to environmental changes. In particular, locomotor trade-offs between endurance or maximal exertion capacity and burst performance capacity have been observed in some species and may constrain the ability of organisms to disperse. Here, we tested for the presence of locomotor trade-offs between maximal exertion and burst performance capacity in an aquatic frog, the tropical clawed frog (Xenopus tropicalis). Given the importance of overland dispersal for this species, we focused on terrestrial exertion capacity (time and distance jumped until exhaustion) and tested whether it trades-off with aquatic burst performance capacity (maximum instantaneous velocity and acceleration), which is likely to be relevant in the context of predator escape and prey capture. Our data show that in both sexes, individuals with longer hindlimbs display higher endurance. Additionally, in females forelimb length was positively correlated with aquatic burst performance capacity and negatively correlated with terrestrial exertion. Trade-offs between endurance and burst performance capacity were detected, but were significant in males only. Finally, males and females differ in morphology and performance. Our data suggest that trade-offs are not universal and may be driven by sex-dependent selection on locomotor capacity. Moreover, our results suggest that locomotor trade-offs may result in sex-biased dispersal under selection for improved endurance capacity as is expected under habitat fragmentation scenarios.