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.

Empirical and theoretical studies have investigated the trade‐offs between reproduction, dispersal and/or survival that may arise between individuals at the range edge of an expanding population. The differential allocation of resources to these life‐history traits may then be constrained by the metabolism of an individual. Previous studies of an invasive expanding population of the frog Xenopus laevis in the West of France showed an increase in allocation of resources to dispersal and a decrease in allocation to reproduction in individuals from the range front. The present study focuses on physiological variation through an analysis of the standard metabolic rate (SMR). SMR was analyzed through measurements of oxygen consumption and carbon dioxide production under resting conditions. Our results show a positive correlation between SMR and individual size and weight, but no difference in body condition is observed between individuals from the center and those from the periphery of the range. Moreover, a decrease in SMR at the periphery was observed in both sexes. Yet, a significant interaction effect between sex and site was observed. Males had a higher SMR than females at the center while females from the periphery showed a higher SMR than males. A lower SMR may allow animals from the periphery to allocate more resources to other functions, such as locomotion, and therefore dispersal. In contrast, the relatively higher SMR in females from the periphery (compared to males) is likely to be driven by the important energetic cost of reproduction in addition to the environmental and demographic constraints at the edge of an expanding population. From the perspective of conservation biology, these results attest to the importance of understanding the biological and evolutionary mechanisms underpinning the selection of traits to estimate the invasive potential of exotic species.

Invasive species are considered as one of the major threats to biodiversity and represent a major challenge in the conservation of natural ecosystems, in preventing damage to agricultural production, and human health risks. Environmental Niche Modelling has emerged as a powerful tool to predict the patterns of range expansion of non-native species and to direct effective strategies for managing biological invasions. The raccoon, Procyon lotor , is a wild mesocarnivore presenting a high adaptability and showing successful introduced populations worldwide. Here, we modelled the current and future climatically favourable areas for the raccoon using two protocols, based on data sets filtrated in geographic and environmental spaces. Projections from these models show extensive current favourable geographical areas covering extensive regions of temperate biomes. Moreover, predictions for 2050 reveals extensive new favourable areas north of the current favourable regions. However, the results of the two modeling approaches differ in the extent of predicted favourable spaces. Protocols using geographically filtered data present more conservative forecasts, while protocol using environmental filtration presents forecasts across greater areas. Given the biological characteristics and the ecological requirements of a generalist carnivore such as the raccoon, the latter forecasts appears more relevant and should be privileged in the development of conservation plans for ecosystems.