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Given the status of the African clawed frog Xenopus laevis as a global amphibian invader, and the potential spread of its invasive populations in Europe and other continents, it is essential to identify the environmental factors and methods that maximize the trapping output of control actions. Cost-effective methods should maximize the number of trapped individuals, and preferably the number of females. We tested five types of attractants in traps, split into two categories: playbacks and conspecific lures, and compared their efficiency in terms of number of trapped individuals (total, females, and males) against the control method currently in use in France (use of food bait). We also estimated the influence of moonlight, an environmental factor known to affect amphibian activity. Playback methods did not increase the capture probability for either sex. In contrast, using a female as a lure allowed us to trap both more individuals (224% compared to the control), more females (186%) and more males (190%), whereas using a male only allowed us to trap more males (167%). These effects were stronger under low moonlight intensity, and at the end of the breeding season. Using female lures appeared to be the best method, both due to a higher number of trapped individuals and a higher number of trapped females. Our study also emphasizes the need for considering the influence of the lunar cycle when planning fieldwork to optimize the cost-efficiency of control actions. We recommend to preferentially set traps under low moonlight intensities. [ABSTRACT FROM AUTHOR]

The description of functional connectivity is based on the quantification of landscape resistance, which represents species‐specific movement costs across landscape features. Connectivity models use these costs to identify movement corridors at both individual and population levels and provide management recommendations for populations of conservation interest. Typically, resistance costs assigned to specific land cover types are assumed to be valid for all individuals of the population. Little attention has been paid to intraspecific variation in resistance costs due to age or dispersal syndrome, which may significantly affect model predictions.We quantified resistance costs in an expanding invasive population of the African clawed frog Xenopus laevis in Western France. In this principally aquatic amphibian, juveniles, sub‐adults and adults disperse overland. The enhancement of dispersal traits via spatial sorting has been also observed at the range periphery of the population. Resistance costs, and thus connectivity, might vary as a function of life stage and position within the invaded range.We assessed multiple dimensions of functional connectivity. On various land cover types, we measured locomotion, as crossing speed, in different post‐metamorphic age classes, and dehydration, sensitivity of locomotion to dehydration and substrate preference in juveniles. We also tested the effect of the position in the invaded range (core vs. periphery) on individual performances.In juveniles, general trends towards higher resistance costs on grass and lower resistance costs on bare soil and asphalt were observed, although not all experiments provided the same cost configurations. Resistance to locomotion varied between age classes, with adults and sub‐adults facing lower costs than juveniles, particularly when crossing structurally complex land cover types such as grass and leaf litter. The position in the range had a minor effect on landscape resistance, and only in the dehydration experiment, where water loss in juveniles was lower at the range periphery.Depicting functional connectivity requires (a) assessing multiple dimensions of behavioural and physiological challenges faced by animals during movement; (b) considering factors, such as age and dispersal syndrome, that may affect movement at both individual and population levels. Ignoring this complexity might generate unreliable connectivity models and provide unsupported management recommendations for conservation. [ABSTRACT FROM AUTHOR]

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 French invasive population was introduced only about 40 years ago suggesting a rapid shift in the thermal physiology. Given that all individuals were acclimated under laboratory conditions at 23°C for 2 months this suggests that the invasive frogs have adapted to their new environment. These data may allow the refinement of physiologically informed species distribution models permitting better estimates of future ranges at risk of invasion. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) is becoming an essential tool for detecting aquatic invasive species and investigating their spread. Surprisingly, this technique has been very rarely used to investigate habitat selection, site occupancy, and colonisation despite its higher capacity to detect many species.The African clawed frog (Xenopus laevis) is a principally aquatic amphibian introduced in several continents from South Africa. In western France, no recent systematic survey of the invasion range has been attempted, mainly because of the elusive nature of the species. Furthermore, the influence of landscape features on invasion has never been investigated, even if adults and juveniles are known to disperse overland and along river networks.Using presence–absence data generated by an eDNA survey conducted across the known invasion front of X. laevis in western France, we aimed to determine whether and how the landscape features surrounding a pond influence the probability that a pond is colonised.Xenopus laevis was detected well beyond the formerly known invasive distribution and at the outward end of some transects, suggesting that we did not reach the actual invasion front in these parts of the range. The landscape variables that best predicted the presence of X. laevis in a pond were topographic wetness index and grass cover within a buffer of 250 m.Higher values of both topographic wetness index and grass cover were negatively related to the occurrence probability. The effects of these two variables more likely to reflect dispersal behaviour than habitat preferences at the pond scale.By combining the high detection probability of eDNA survey techniques and a landscape ecology approach, we may gain valuable insight into the colonisation process of water bodies by elusive invasive species. Such information is crucial to prevent access to specific sites and locate invasion front areas where connectivity can be disrupted, thus increasing the effectiveness of management countermeasures. [ABSTRACT FROM AUTHOR]

Amphibians are now recognized as the most endangered group. One of this decline causes is the degradation of their habitat through direct contamination of water, soil leaching, or runoff from surrounding contaminated soils and environments. In the North of France, the extensive industrial activities resulted in massive soil contamination by metal compounds. Mineral amendments were added to soils to decrease trace metal mobility. Because of the large areas to be treated, the use of inexpensive industrial by-products was favored. Two types of fly ashes were both tested in an experimental site with the plantation of trees in 2000. Aim of the present work was to investigate the effects of extracts from metal-contaminated soils treated or not for 10 years with fly ashes on Xenopus laevis oocyte using cell biology approaches. Indeed, our previous studies have shown that the Xenopus oocyte is a relevant model to study the metal ion toxicity. Survival and maturation of oocyte exposed to the soil extracts were evaluated by phenotypic approaches and electrophysiological recordings. An extract derived from a metal-contaminated soil treated for 10 years with sulfo-calcic ashes induced the largest effects. Membrane integrity appeared affected and ion fluxes in exposed oocytes were changed. Thus, it appeared that extracted elements from certain mineral amendments used to prevent the mobility of metals in the case of highly metal-contaminated soils could have a negative impact on X. laevis oocytes. [ABSTRACT FROM AUTHOR]

When species are translocated to a novel environment, individuals become exposed to new predators against which they may not express very efficient defences at least at an initial stage. The strength of anti-predator defence is an important parameter that may determine the ability of local communities to control the expansion of invasive populations. The African clawed frog, Xenopus laevis, is a globally invasive amphibian that has successfully established invasive populations on four continents. In its invasive distribution in western France, X. laevis encounters novel aquatic predators. Some may be related to the predators in the native range but others may belong to different taxonomic groups and not be functionally or ecologically equivalent. We tested whether naïve X. laevis tadpoles from the invasive French population exhibit anti-predator response to local predators, and whether the response depends on the degree of relatedness with predators encountered in the native range of the frog, or whether individuals may express generic neophobia to any cue they are not familiar with. We exposed naïve lab-reared tadpoles to a native non-predatory water snail, Planorbarius corneus, a native predatory beetle, Dytiscus dimidiatus, and an invasive predatory crayfish, Procambarus clarkii. We found that X. laevis tadpoles innately reduce their activity when exposed to beetle and crayfish stimulus cues, but not to snails. Reducing activity can decrease the probability of being detected by predators. This demonstrates that invasive tadpoles respond to known and novel predators regardless of the evolutionary history. Whether the produced response is always effective against a totally novel predator remains to be tested. [ABSTRACT FROM AUTHOR]

In expanding populations, the allocation of resources to life-history traits is expected to change rapidly after the colonization of a new area. Understanding these changes is of crucial importance to predict the future changes in distribution ranges, and the possible impacts of expanding species on the colonized environments. Both theoretical and empirical studies have provided some evidence for an increased dispersal at the range edge of expanding populations. Because this phenomenon has been documented on large spatial scales, it seems difficult to determine what proportion of the phenotypic variation is due to the expansion process (spatial sorting) versus spatial variation in the environment (local adaptation). The aim of our study is to determine whether, in a small and recent expanding population, the dispersal capacity is increased at the range edge compared to the range core despite a minimal role of local adaptation. We studied the modification of dispersal capacity at the range edge of an expanding population of the African clawed frog, Xenopuslaevis recently settled in Western France. To do so, we used experiments to compare movements of individuals depending on their location in the population, and capture–mark–recapture field surveys to estimate variation in traits related to dispersal across the invasive range. Both methods consistently showed significantly higher dispersal rates and distances, as well as in the relative length of the hind limb, at the range edge, for both sexes. This result is the first report suggesting that changes in allocation to dispersal, and not only traits associated with dispersal, can occur at a small geographical and temporal scale, where the role of local adaptation is likely minimal. This study fills a gap in an issue where it is currently crucial, for conservation purposes, to understand the mechanisms involved in range expansions. [ABSTRACT FROM AUTHOR]

The goal of this laboratory course is to introduce vertebrate developmental biology to undergraduate students, emphasizing both classical and contemporary aspects of this field. During the course, the students combine the use of living Xenopus laevis material with active tutorial participation, with the aim of illustrating how the fertilized egg can generate the diversity of cell types and complexity of pattern seen only a few days later in the embryo. Special emphasis is given to the observation and manipulation of living material. The laboratory course includes a comprehensive analysis of both oogenesis and early development and is divided into two overlapping parts that combine tutorial and practical approaches. The first part is devoted to oogenesis; oocytes are sorted out, allowed to mature in vitro and observed in histological section. In the second part, students perform an in vitro fertilization of Xenopus eggs and a mesoderm and neural induction assay of animal cap explants. Successful induction of the explants is confirmed by morphological, histological and molecular analyses. Finally, the students observe and comment on selected slides to illustrate the organization of the body plan of the amphibian embryo at an early stage of organogenesis.