Julien Courant

Invasive species represent a unique opportunity to study the evolutionary mechanisms driving range expansions. Although range expansion is expected to be associated with increased reproduction and dispersal at the range edge, Xenopus laevis seems to decrease its reproductive investment and to enhance dispersal at the range edge. Evidence of increased dispersal at the edge of expanding populations occurring simultaneously with a faster growth rate has been reported for other organisms. Here, we focused on the growth rate and age structure at the range edge vs. the range core in an expanding population of X. laevis. We used skeletochronology to characterize the age of 250 individuals captured at the range core and edge of this expanding population. Using the Von Bertalanffy equation, we then compared individual growth rates between locations. We found no significant changes in growth rate or age structure between edge and core samples. This result suggests that the reduced investment ...

In this paper we studied the diet in four allopatric populations of alpine salamanders in the Dinarides (Salamandra atra prenjensis). Food consumption was assessed by stomach flushing while food availability by pitfall traps and netting. We aimed to: (i) assess the realized dietary niche, (ii) investigate prey preferences, (ii) explore individual specialization, clustering and nestedness. All populations have an equally wide dietary span that is among the largest reported for terrestrial salamanders. On the other hand, the amount of ingested prey is rather low compared to other salamander species; the quantity of consumed prey did not differ among populations but younger individuals fed more than adults. Food composition somewhat differed among populations but not among sex/age classes. In all four populations, the bulk of diet consisted of beetles, spiders, snails and millipedes; except for beetles, such prey was also preffered together with centipedes and isopods. For most of the ...

Although of crucial importance for invasion biology and impact assessments of climate change, it remains widely unknown how species cope to environmental conditions beyond their currently realized climatic niches (i.e., those climatic conditions existing populations are exposed to). The African clawed frog Xenopus laevis, native to southern Africa, has established numerous invasive populations on multiple continents making it a pertinent model organism to study environmental niche dynamics. In this study, we assess whether the realized niches of the invasive populations in Europe, South, and North America represent subsets of the species' realized niche in its native distributional range or if niche shifts are traceable. If shifts are traceable, we ask whether the realized niches of invasive populations still contain signatures of the niche of source populations what could indicate local adaptations. Univariate comparisons among bioclimatic conditions at native and invaded range...

As invasive species are one of the principal threats on global biodiversity, assessing their impact is a crucial element of conservation biology. Quantifying the possible impacts of an invasive population represents the first step in the establishment of efficient management plans. In this study, we applied a method of site-occupancy modeling to estimate the influence of an invasive frog, Xenopus laevis, on the amphibian species richness in western France. In our analyses we took into account habitat characteristics (i.e. the size and general shape of the ponds), the structure of the aquatic vegetation, the presence of other vertebrates, and the physicochemical parameters of the pond. Richness was negatively related to the abundance of X. laevis and to the time since colonization as estimated by the distance of the pond to the site of introduction. Habitat niche breadth of native amphibians did not differ between invaded and non-invaded areas. This might be a consequence of the homo...

Although of crucial importance for invasion biology and impact assessments of climate change, it remains widely unknown how species cope with and adapt to environmental conditions beyond their currently realized climatic niches (i.e., those climatic conditions existing populations are exposed to). The African clawed frog Xenopus laevis, native to southern Africa, has established numerous invasive populations on multiple continents making it a pertinent model organism to study environmental niche dynamics. In this study, we assess whether the realized niches of the invasive populations in Europe, South, and North America represent subsets of the species' realized niche in its native distributional range or if niche shifts are traceable. If shifts are traceable, we ask whether the realized niches of invasive populations still contain signatures of the niche of source populations what could indicate local adaptations. Univariate comparisons among bioclimatic conditions at native an...

Invasive species like the African clawed frog, Xenopus laevis (Daudin, 1803) usually have a diet able to impact local aquatic communities. The diet of Xenopus laevis has already been studied both in its original distribution area and in some areas where it has been introduced. In France, this part of the ecology of the species has not been studied yet. This article presents the results obtained from dissections realized on individuals coming from ponds in the Deux-Sèvres department, few kilometres away from the introduction locality of the species. The diet shows an important variety of preys, with an unmistakable predilection for aquatic preys. An analysis by occurrence frequency has highlighted other groups, like adult Lepidoptera, which represented an important ratio of identified preys.

A cause de l’actuel declin mondial de la biodiversite, la comprehension des consequences de chaque menace sur la biodiversite est un element crucial en biologie de la conservation. Les especes exotiques envahissantes representent une de ces menaces a l’echelle mondiale, et peuvent induire localement des dommages au sein des ecosystemes. Etudier les phenomenes regissant les effets negatifs de ces especes, et leurs potentiels d’expansion apparait actuellement comme un element crucial pour determiner leurs effets sur le long terme. Dans cette etude, nous focalisons nos efforts sur une population exotique envahissante du Xenope lisse, Xenopus laevis, en France, pour apporter de nouvelles connaissances sur les interactions de cette population avec son environnement et pour etudier les changement dans l’allocation des ressources aux traits d’histoire de vie lies a la reproduction la survie et la dispersion durant l’expansion de l’aire de repartition. Nous etudions le regime alimentaire de...

Over the past 22 years, annual mean temperatures have increased by 1°C in Qatar and even greater increases are projected in the future. Since lizards depend on thermoregulation to survive, how do such rises in air temperature affect the Eastern sandfish Scincus mitranus in Qatar? S. mitranus exclusively inhabit Barchan dunes, which are restricted to the South-Eastern region of the country and are currently disappearing due to the North-Westerly Al Shamal winds driving them into the sea. Loss of this ecosystem, coupled with climate change pose serious risk to the survival of S. mitranus. Our study was carried out in two tiers. In the first we set out to estimate dune-dependent population densities, while in the second tier of the study we observed sandfish activity in relation to soil temperature. Sandfish (106) were captured and tagged from 5 terrestrial Barchan dunes in Qatar over a period of 10 months. The captured sandfish ranged from 6 to 29 cm in length and, weighed between 2 and 47 g. Sandfish popul...

Temperature is a critical abiotic factor impacting all aspects of the biology of organisms, especially in ectotherms. As such, it is an important determinant of the potential invasive ability of organisms and may limit population expansion unless organisms can physiologically respond to changes in temperature either through plasticity or by adapting to their novel environment. Here, we studied the African clawed frog, Xenopus laevis, which has become invasive on a global scale. We compared adults from an invasive population of western France with individuals from two populations in the native range in South Africa. We measured the thermal dependence of locomotor performance in adults given its relevance to dispersal, predator escape, and prey capture. Our results show significant differences in the limits of the 80% performance breadth interval for endurance with the French population showing a left shift in its limits congruent with the colder climate experienced in France. The Fre...

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 a...

Invasive species are among the most significant threats to biodiversity. The diet of invasive animal populations is a crucial factor that must be considered in the context of biological invasions. A broad dietary spectrum is a frequently cited characteristic of invasive species, allowing them to thrive in a wide range of environments. Therefore, empirical studies comparing diet in invasive and native populations are necessary to understand dietary requirements, dietary flexibility, and the associated impacts of invasive species. In this study, we compared the diet of populations of the African clawed frog, Xenopus laevis in its native range, with several areas where it has become invasive. Each prey category detected in stomach contents was assigned to an ecological category, allowing a comparison of the diversity of ecological traits among the prey items in the diet of native and introduced populations. The comparison of diets was also performed using evenness as a niche breadth in...

By altering or eliminating delicate ecological relationships, non-indigenous species are considered a major threat to biodiversity, as well as a driver of environmental change. Global climate change affects ecosystems and ecological communities, leading to changes in the phenology, geographic ranges, or population abundance of several species. Thus, predicting the impacts of global climate change on the current and future distribution of invasive species is an important subject in macroecological studies. The African clawed frog (Xenopus laevis), native to South Africa, possesses a strong invasion potential and populations have become established in numerous countries across four continents. The global invasion potential of X. laevis was assessed using correlative species distribution models (SDMs). SDMs were computed based on a comprehensive set of occurrence records covering South Africa, North America, South America and Europe and a set of nine environmental predictors. Models were built using both a maximum entropy model and an ensemble approach integrating eight algorithms. The future occurrence probabilities for X. laevis were subsequently computed using bioclimatic variables for 2070 following four different IPCC scenarios. Despite minor differences between the statistical approaches, both SDMs predict the future potential distribution of X. laevis, on a global scale, to decrease across all climate change scenarios. On a continental scale, both SDMs predict decreasing potential distributions in the species' native range in South Africa, as well as in the invaded areas in North and South America, and in Australia where the species has not been introduced. In contrast, both SDMs predict the potential range size to expand in Europe. Our results suggest that all probability classes will be equally affected by climate change. New regional conditions may promote new invasions or the spread of established invasive populations, especially in France and Great Britain.

Due to both deliberate and accidental introductions, invasive African Clawed Frog (Xenopus laevis) populations have become established worldwide. In this study, we investigate the geographic origins of invasive X. laevis populations in France and Portugal using the phylogeographic structure of X. laevis in its native South African range. In total, 80 individuals from the whole area known to be invaded in France and Portugal were analysed for two mitochondrial and three nuclear genes, allowing a comparison with 185 specimens from the native range. Our results show that native phylogeographic lineages have contributed differently to invasive European X. laevis populations. In Portugal, genetic and historical data suggest a single colonization event involving a small number of individuals from the south-western Cape region in South Africa. In contrast, French invasive X. laevis encompass two distinct native phylogeographic lineages, i.e., one from the south-western Cape region and one from the northern regions of South Africa. The French X. laevis population is the first example of a X. laevis invasion involving multiple lineages. Moreover, the lack of population structure based on nuclear DNA suggests a potential role for admixture within the invasive French population.