Theoretical models predict that spatial sorting at the range edge of expanding populations should favor individuals with increased mobility relative to individuals at the center of the range. Despite the fact that empirical evidence for the evolution of locomotor performance at the range edge is rare, data on cane toads support this model. However, whether this can be generalized to other species remains largely unknown. Here, we provide data on locomotor stamina and limb morphology in individuals from two sites: one from the center and one from the periphery of an expanding population of the clawed frog Xenopus laevis in France where it was introduced about 30 years ago. Additionally, we provide data on the morphology of frogs from two additional sites to test whether the observed differences can be generalized across the range of this species in France. Given the known sexual size dimorphism in this species, we also test for differences between the sexes in locomotor performance and morphology. Our results show significant sexual dimorphism in stamina and morphology, with males having longer legs and greater stamina than females. Moreover, in accordance with the predictions from theoretical models, individuals from the range edge had a greater stamina. This difference in locomotor performance is likely to be driven by the significantly longer limb segments observed in animals in both sites sampled in different areas along the range edge. Our data have implications for conservation because spatial sorting on the range edge may lead to an accelerated increase in the spread of this invasive species in France.
The authors declare no competing or financial interests.
A.H. devised the study; J.C. captured animals in the field; V.L. performed the locomotor trials; V.L. and A.H. analyzed the data; all authors contributed to the writing of the manuscript.
Funded by a BiodivERsA ERA-NET project entitled ‘Invasive biology of Xenopus laevis in Europe: ecology, impact and predictive models’ (INVAXEN).
- Received July 21, 2016.
- Accepted October 26, 2016.
- © 2017. Published by The Company of Biologists Ltd