BackgroundMetamorphosis is a key event in the life history of many organisms, including amphibians, because it can involve abrupt changes in morphology and habitat. However, metamorphosis can also be bypassed by paedomorphic processes that allow reproduction at the larval stage. The evolution of these alternative developmental processes depends on the payoffs of life in larval and adult environments, as well as the cost of transition. Previous studies on the cost of metamorphosis have focused on the larval stage, which is still subject to the achievement of a minimal size threshold as well as growth to adulthood. Therefore, facultatively paedomorphic species could be valuable models for testing the direct costs of metamorphosis. This is because facultative paedomorphs are sexually dimorphic adults that are capable of metamorphosis.ResultsBy modelling weight loss using an experimental, longitudinal design that manipulated the ecological drivers of metamorphosis in a facultatively paedomorphic amphibian, the palmate newt (Lissotriton helveticus), we found that metamorphosis imposes costs in terms of body weight, whereas temperature has a smaller effect. In contrast, newts that do not metamorphose did not lose weight. The costs were sex-related with females at a disadvantage during metamorphosis. Furthermore, the decrease in food consumption associated with metamorphosis resulted in a loss of body weight.ConclusionsOverall, these results emphasise the importance of considering direct costs when studying the evolutionary ecology of metamorphosis. They also show that polymorphic species are suitable models for investigating the drivers of metamorphosis and its loss in micro- and macroevolution.

Top predators strongly influence food webs, often because they reach large body sizes. Amphibians are typically regarded as prey in such systems, but giant salamanders are a rare exception. Because gigantism entails extreme ontogenetic body size variation, it is expected to drive strong trophic niche shifts and reshape interactions within and among species as individuals grow. However, such trophic shifts in giant amphibians and relationships with other consumers remain largely unexplored, limiting our understanding of the contribution of this flagship species to river food web structure. Here, we used stable isotope analysis (δ13C-δ15N) to investigate the trophic structure of a freshwater community dominated by the Japanese giant salamander (Andrias japonicus). We assessed how extreme ontogenetic body size variation modifies intra- and interspecific interactions and contributes to overall community structure. We also quantified the dominant carbon sources fueling the community, and modeled trophic positions (TPs), niche metrics, and relationships of all major consumer species. By sampling 161 giant salamanders and approximately 700 other consumers for stable isotope analysis, we provide the first comprehensive characterization of food web structure in a freshwater community dominated by A. japonicus. We found clear trophic shifts: smaller individuals overlapped with mesopredators (fish, prawns, turtles), suggesting potential competition, whereas TP increased with size, placing larger individuals above other predators, at the top of the food web. Large salamanders broadened the community δ15N range, contributing significantly to the trophic evenness and total community niche space. Basal source tracing revealed that both aquatic and terrestrial energy pathways sustained the food web. Overall, these findings show that gigantism in A. japonicus shapes trophic hierarchies, contributing significantly to vertical complexity and trophic diversity of the community, and highlighting how ontogenetic shifts in giant predators can structure riverine food webs. By integrating isotopic niches, TP, and basal source contributions at the whole-community scale, this study provides a generalisable framework for linking predator ontogeny to food web structure, with direct relevance for conserving vulnerable freshwater ecosystems; endangered top predators such as A. japonicus may contribute disproportionately to food web resilience and community structure.

The worldwide introductions of mosquitofish Gambusia holbrooki as a biocontrol agent is one of the biological invasions posing a significant threat to freshwater biodiversity, exerting strong ecological pressure on native organisms. However, the impact of mosquitofish on the functioning of aquatic communities is not well understood. In this study, we investigated its effects on the functionality of invertebrate communities across a large number of ponds in Croatia. Taxonomic inventories and functional trait matrices were combined to evaluate changes in community structure and ecosystem functioning. Multivariate analyses (dbRDA, PERMANOVA, SIMPER) revealed that the presence of mosquitofish significantly alters community composition, reducing both taxonomic and functional diversity and selecting for traits associated with predation resistance. Ponds invaded by mosquitofish showed signs of biotic homogenisation, with generalist, resistant taxa dominating. These results emphasise the ability of mosquitofish to simplify trophic architecture and reduce functional redundancy, which could have long-term consequences for ecosystem resilience.

Habitat fragmentation is a major driver of global biodiversity loss, and amphibians are particularly sensitive to this threat. In riverine ecosystems, dams cause longitudinal disconnection, especially affecting fully aquatic species. Across North America, China, and Japan, giant salamanders inhabit rivers where they exert key ecological roles. As strictly aquatic species, dams may severely reduce habitat connectivity and compromise their long-term population viability. In this context, we assessed the fragmentation risk faced by Japanese giant salamander (Andrias japonicus) populations in Japan by compiling a detailed inventory of dams in eight watersheds where the species occurs. We adapted a Dam Fragmentation Index (DFI), taking into account density and height of dams, and the presence of fishways, to quantify fragmentation levels. A total of 2,434 river barriers were identified, with only five percent equipped with fishways potentially usable by giant salamanders. DFI scores indicated moderate to very high fragmentation levels. Moreover, salamander locations were on average at 587 m from barriers. These findings suggest that river fragmentation represents a major threat to the long-term viability of A. japonicus populations by disrupting movements needed for breeding and gene flow. Conservation actions are urgently needed, including the implementation of suitable passage structures such as salamander-adapted ladderways, and the integration of this species' ecological needs into future river management plans. Our study provides a new framework to quantify barrier impact on amphibians and highlights the importance of addressing river connectivity for the conservation of freshwater biodiversity.

Abstract The olm, Proteus anguinus , is one of the most iconic vertebrates of Europe. Since its scientific description in 1768, its extreme adaptations to subterranean life in the enigmatic underground waters of the Dinaric Karst have fascinated scholars and naturalists worldwide for more than two centuries. Yet, the evolution and taxonomic diversity of its populations remained largely unresolved, as complex patterns of phenotypic differentiation and molecular variation collide with an intricate nomenclatural history. In this work, we review recent biogeographic advances, notably based on range-wide phylogeographic analyses implementing genomic data, and combined with distributional data, species distribution modelling, red list assessment, morphological analyses and a critical species delimitation evaluation, recognize nine species in immediate danger of extinction. Based on an extensive nomenclatural search, we determined that six correspond to available names and three are newly described in this work. These species all exhibit highly restricted distributions within the Dinaric karst, collectively representing an exceptional example of subterranean microendemism among European vertebrates. Linking influential historical research with modern zoological methods, this revision provides an up-to-date science-based taxonomic framework for future studies of comparative evolution and ecology of Proteus , while establishing a sound basis for species-level conservation management of one of Europe’s most remarkable vertebrate diversifications.

Abstract The Balkan Peninsula hosts a great proportion of Europe’s biodiversity, and this is well illustrated by amphibian richness and endemism. Among them, the yellow-bellied toad Bombina variegata has been a model in ecology and evolution, but several aspects of its phylogeography and taxonomy remain surprisingly poorly understood. In this study, we combine cytochrome b DNA barcoding data (1238 individuals from 355 localities), mitogenome phylogenetics (17.2 kb), gene-based nuclear phylogenetics (3.7 kb from four gene fragments) and multilocus phylogenomics (4759 loci / ~554 kb obtained by double digest Restriction Associated DNA sequencing; ddRAD-seq) to re-assess the diversification of B. variegata, and revisit its nomenclatural history to assign scientific names to phylogeographic lineages. The analyses support four major lineages, one assigned to B. v. variegata (Carpathians and northwestern ranges), one assigned to B. v. pachypus (Apennine Peninsula), and two assigned to B. v. scabra (Dinarides, Hellenides and Balkanides vs. the Rhodope mountains). Spatiotemporal patterns of diversification suggest a role for a Late Miocene marine incursion in the Pannonian Plain (Paratethys) as the initial trigger of divergence, followed by a vicariance event in the Apennines and a “sky island” process of Pleistocene differentiation in the Balkan Peninsula. As it reached the Dinarides during the Late Pleistocene, B. v. variegata potentially hybridized with B. v. scabra and captured its mitochondrial DNA, which resulted in a massive cyto-nuclear discordance across all northwestern European populations. Finally, we show that the two lineages of B. v. scabra significantly differ in morphology and ventral coloration patterns, and describe the Rhodope lineage as a new subspecies.

Facultative paedomorphosis is a widespread polyphenism in newts and salamanders, but it is declining due to the introduction of non-native species. Conversely, caudates have often been introduced outside their range and could be good models to improve our understanding of the factors that facilitate the expression of metamorphosis versus paedomorphosis. In particular, the alpine newt is a common amphibian species that has been introduced into many countries and whose many native paedomorphic populations have become extinct. By surveying ponds where metamorphic alpine newts were introduced in France over eight years, this study aimed to show what we can learn from such introduced populations by highlighting key life history traits of both phenotypes and a co-existing native species, the palmate newt, that can also express paedomorphosis. Although paedomorphosis is rare outside of the main European hotspots, paedomorphs were repeatedly found in the introduced population, including in a pond where they were dispersing. Interestingly, the relative frequencies of paedomorphs in the adult population of both species were low and match those of the paedomorphs of the native palmate newts over the years. This resulted in a complex size-structured newt community. Taken together, these results allow the discussion of alternative scenarios for the origin of aliens and possible reasons for the presence of paedomorphs in such populations. Ultimately, they call for reporting such developmental variants in the introduced populations of newts and salamanders and tracing the origin of the introductions to infer on genetic and environmental causes.

Giant salamanders are the world’s largest amphibians and keystone predators in riverine ecosystems where they face global declines. Identifying environmental variables influencing their distribution is, therefore, an essential step for their conservation. This study aims to assess the current habitat suitability and distribution of the Japanese giant salamander ( Andrias japonicus ) and to predict changes under future climate scenarios. We used species distribution models (SDMs) over a 282,916 km² area, including 477 high-resolution occurrence data of giant salamanders and seven remote-sensing environmental predictors (climatic, topographic and land use). We projected the prediction maps, identified the most contributing variables and calculated the shifts of suitable areas for three periods (2050, 2070 and 2090) under projected climatic conditions. Climatic variables highly contributed to the distribution of giant salamanders (76% of the total), with preferences for areas with moderate precipitations during cold and wet seasons and mild summer temperatures. A moderately steep surrounding environment was favourable for salamanders, whereas the land-use variables had less influence. Future climate predictions indicate a major decrease of suitable areas. Altogether, our results highlight the habitat preferences of giant salamanders at a broad scale and the negative impact of climate change on future suitable areas. These findings provide important steps for upcoming conservation actions for this threatened species in delineating favourable distribution ranges and priority areas that should be directly affected by climate change. Finally, they emphasise the need for new research at a fine scale on disturbances to the aquatic habitat to enhance the conservation of giant salamanders. We used a species distribution model (MaxEnt), high-resolution occurrence data and remote sensing data (climatic, topographic and land use) to identify suitable habitats for the Japanese giant salamander in Japan. The most suitable environments for the Japanese giant salamander are located both within and beyond its current distribution range, with the ‘Japanese Alps’ forming an impassable natural barrier. Among the variables studied, precipitation of the warmest quarter, precipitation of the coldest quarter, mean temperature of the warmest quarter and mean temperature of the wettest quarter were the most important environmental predictors of the species’ distribution. Climate change is expected to severely reduce the potential suitable geographical areas for the Japanese giant salamander in the future. The present work calls for new surveys based on the projected maps to improve the mapping of salamander distribution and to focus on ecological features and threats at the aquatic habitat level to understand the risks to their populations.

In predators, growth often drives ontogenetic dietary shifts (ODSs), leading to increasing trophic position (TP) with body size as growing individuals gradually incorporate larger prey in their diet. In species exhibiting extreme size variation, particularly those with gigantism, TP may increase markedly with body size, as large individuals might gain access to prey considerably higher in the food chain and inaccessible to smaller conspecifics. This can ultimately lead to apex predator status in the largest individuals. In this study, we investigated for the first time ODSs in one of the world's largest amphibians, the Japanese giant salamander Andrias japonicus. We combined stomach content and stable isotope analysis (delta 15N, delta 13C) from 160 individuals across a broad size range to quantify dietary patterns and TP changes. We found a non-linear increase in TP with body size, from approximately 3.0-5.1, with a marked inflection point at a snout-vent length of 39 cm. This threshold corresponded to a clear dietary transition: from primarily consuming aquatic insects, to feeding predominantly on fish, anurans, and freshwater crabs. This transition likely reflects morphological and physiological adaptations associated with gigantism, enabling the exploitation of large prey. Our findings suggest that gigantism may be adaptive in predators such as giant salamanders by promoting ecological opportunities, allowing individuals to access high trophic levels through extensive growth and ultimately function as apex predators. These results contribute to a broader understanding of the ecological consequences of body size evolution in predatory vertebrates, highlighting how extreme growth can reshape species' ecological roles.

Invasive alien anurans are introduced worldwide in freshwater ecosystems where they can have a strong impact on native organisms such as amphibians. The risk for natives is dependent on the degree of niche overlap and co-occurrence in pond-breeding sites. In the present study, we focused on alien marsh frogs (Pelophylax ridibundus) that are invading nationwide areas in Western Europe and which prey on both caudates and anurans. We assessed aquatic habitat preferences, pond use and environmental niche overlap between invasive populations of marsh frogs and five species of native amphibian prey of the Larzac plateau (southern France). Due to their large environmental niche, marsh frogs have become the most ubiquitous amphibians in the area. Occupancy models revealed that they had aquatic habitat preferences (e.g., water depth and aquatic vegetation) similar to most species of native amphibians. This resulted in a large overlap between the environmental niche of the invader and its potential prey. The frequent coexistence in ponds therefore exposed native species to predation risk and other potential disturbances caused by marsh frogs. Altogether, these results highlight on the risks posed by such opportunist invaders for native amphibians that occur in their wide invasion range.

In a global context of invasive alien species (IAS), native predators are often eradicated by functionally different IAS, which may induce complex cascading consequences on ecosystem functioning because of the key role predators play in structuring communities and stabilizing food webs. In permanent ponds, the most abundant freshwater systems on Earth, global human-mediated introductions of alien omnivores such as the pet trade goldfish are driving broad-scale patterns of native predators' exclusion, but cascading consequences on food web structure and functioning are critically understudied. We compared food webs of naturally fishless ponds versus ponds where dominant native predators (newts) had been extirpated by invasive goldfish within the last decade. Integrating community-wide isotopic, taxonomic and functional traits approaches, our study reveals that pond food webs collapsed in both vertical and horizontal dimensions following goldfish introduction and the associated exclusion of native predators. Consumer taxonomic diversity was drastically reduced, essentially deprived of amphibians as well as predatory and mobile macroinvertebrates to the profit of burrowing, lower trophic level consumers (detritivores). Changes in community structure and function underlined a regime shift from a macrophyte-dominated system mainly characterized by benthic primary production (periphyton), to a macrophyte-depleted state of ponds hosting communities mainly associated with phytoplankton primary production and detritus accumulation, with higher tolerance to eutrophication and low dissolved oxygen concentration. Results underline major impacts of widely introduced omnivores such as the goldfish on the functioning of pond ecosystems with potentially dramatic consequences on the key ecosystem services they deliver, such as global biodiversity support or water quality improvement. They also shed light on the key role of submerged aquatic vegetation in supporting diverse communities and complex food webs in shallow lentic systems and call for urgent consideration of threats posed by IAS on ponds' ecosystems by managers and policymakers.

Global warming can either promote or constrain the invasive potential of alien species. In ectotherm invaders that exhibit a complex life cycle, success is inherently dependent on the capacity of each developmental stage to cope with environmental change. This is particularly relevant for invasive anurans, which disperse on land while requiring water for reproduction. However, it remains unknown how the different life stages respond in terms of energy expenditure under different climate change scenarios. We here quantified the oxygen uptake of frogs at rest (a proxy of the standard metabolic rate) in the aquatic phase (at the tadpole and climax, i.e. during metamorphosis, stages) and in the terrestrial phase (metamorphosed stage) at three environmental temperatures. To do so, we used marsh frogs (Pelophylax ridibundus), an amphibian with the largest invasive range within the palearctic realm and for which their adaptation to global warming might be key to their invasion success. Beyond an increase of metabolic rate with temperature, our data show variation in thermal adaptation across life stages and a higher metabolic cost during metamorphosis. These results suggest that the cost to shift habitat and face changes in temperature may be a constraint on the invasive potential of species with a complex life cycle which may be particularly vulnerable during metamorphosis.

Palearctic water frogs (genus Pelophylax ) are an outstanding model in ecology and evolution, being widespread, speciose, either threatened or threatening to other species through biological invasions, and capable of siring hybrid offspring that escape the rules of sexual reproduction. Despite half a century of genetic research and hundreds of publications, the diversity, systematics and biogeography of Pelophylax still remain highly confusing, in no small part due to a lack of correspondence between studies. To provide a comprehensive overview, we gathered >13,000 sequences of barcoding genes from >1700 native and introduced localities and built multigene mitochondrial (~17 kb) and nuclear (~10 kb) phylogenies. We mapped all currently recognized taxa and their phylogeographic lineages (>40) to get a grasp on taxonomic issues, cyto-nuclear discordances, the genetic makeup of hybridogenetic hybrids, and the origins of introduced populations. Competing hypotheses for the molecular calibration were evaluated through plausibility tests, implementing a new approach relying on predictions from the anuran speciation continuum. Based on our timetree, we propose a new biogeographic paradigm for the Palearctic since the Paleogene, notably by attributing a prominent role to the dynamics of the Paratethys, a vast paleo-sea that extended over most of Europe. Furthermore, our results show that distinct marsh frog lineages from Eastern Europe, the Balkans, the Near East, and Central Asia ( P. ridibundus ssp.) are naturally capable of inducing hybridogenesis with pool frogs ( P. lessonae ). We identified 14 alien lineages (mostly of P. ridibundus ) over ~20 areas of invasions, especially in Western Europe, with genetic signatures disproportionally pointing to the Balkans and Anatolia as the regions of origins, in line with exporting records of the frog leg industry and the stocks of pet sellers. Pelophylax thus emerges as one of the most invasive amphibians worldwide, and deserves much higher conservation concern than currently given by the authorities fighting biological invasions.

Quantifying rarity at the intraspecific level is an important task for conservation biologists because rare phenotypes have a higher extinction risk than common ones. However, quantitative assessments of rarity are lacking at this level, preventing to adequately protect rare and endangered variants that are part of the pool of common species. Our aim was to take benefit of high-resolution volunteer-based occurrence data to assess quantitatively rarity patterns of facultative paedomorphosis, in the Alpine newt (Ichthyosaura alpestris). This polyphenism is composed of two morphs, a rare adult phenotype retaining gills and a common phenotype metamorphosing. We included multiple spatial scales (i.e., resolution) and combined 15,613 occurrence records from the atlas databases of the seven countries in the European Alps to understand how spatial scale may affect rarity metrics. Our analyses revealed that the rarer phenotype was 292 times rarer than the common phenotype, occupying a very small and fragmented area of occupancy. Yet, rarity depended on the spatial resolution of the data. Rarity estimates were up to 1300 times lower at the coarser than at the finer spatial scale. Both the rarity of the rare phenotype and the presence of threats (i.e., fish introductions) make paedomorphs critically endangered whereas the common phenotype was widespread at all spatial scales. Altogether, these results show how rarity metrics can differ between spatial scales for rare and common organisms, suggesting that fine-grain data should be used to assess intraspecific rarity. They also show that combining datasets from distribution atlases is efficient to estimate rarity.

Alien predator introduction is a global threat to amphibians. Yet, there is a lack of in situ studies of trophic interactions between alien predators and native amphibians, particularly concerning small predatory fish such as mosquitofish. Mosquitofish originate from the United States but have been introduced globally, including intentionally for mosquito control. They cause declines in many amphibian populations but the mechanisms involved have been seldom investigated. Trophic interaction studies (mainly ex situ) reveal negative effects on larval amphibian stages but do not consider interactions with adults. Some site-occupancy studies show no negative association with adult amphibians, suggesting potentially complex demographic impacts and calling for a better characterization of trophic interaction with adult amphibians. Here, we studied in situ trophic interactions between introduced Eastern mosquitofish (Gambusia holbrooki) and pond-breeding palmate newts (Lissotriton helveticus; larvae and adults) using gut content and stable isotope analyses. Mosquitofish had little trophic niche overlap with adult newts. Adult newts foraged mainly on burrowing benthic macroinvertebrates that were little exploited by mosquitofish, the latter focusing mainly on microcrustaceans. Both techniques suggested predation on newt eggs or larvae and cannibalism by mosquitofish. Since native newts were still abundant despite > 50 years of mosquitofish presence and reproductively active but without evidence of larval survival, we argue that ponds invaded by small predatory fish such as mosquitofish may pose a risk by acting as demographic sinks for newts due to their predatory impact on larvae and eggs, but potentially low impact on adults in terms of trophic niche overlap.

Climate change and invasive species are two major drivers of biodiversity loss and their interaction may lead to unprecedented further loss. Invasive ectotherms can be expected to tolerate temperature variation because of a broad thermal tolerance and may even benefit from warmer temperatures in their new ranges that better match their thermal preference. Multi-trait studies provide a valuable approach to elucidate the influence of temperature on the invasion process and offer insights into how climatic factors may facilitate or hinder the spread of invasive ectotherms. We here used marsh frogs, Pelophylax ridibundus , a species that is invading large areas of Western Europe but whose invasive potential has been underestimated. We measured the maximal and minimal temperatures to sustain physical activity, the preferred temperature, and the thermal dependence of their stamina and jumping performance in relation to the environmental temperatures observed in their invasive range. Our results showed that marsh frogs can withstand body temperatures that cover 100% of the annual temperature variation in the pond they live in and 77% of the observed current annual air temperature variation. Their preferred body temperature and performance optima were higher than the average temperature in their pond and the average air temperature experienced under the shade. These data suggest that invasive marsh frogs may benefit from a warmer climate. Broad thermal tolerances, combined with high thermal preferences and traits maximised at high temperatures, may allow this species to expand their activity period and colonise underexploited shaded habitat, thereby promoting their invasion success.

Fish introduction into fishless high-altitude lakes has detrimental effects on biodiversity. Removal of alien fish through intensive fishing is cost-intensive and difficult to achieve in productive lakes. Lake Sulzkarsee is the only lake in the National Park Gesäuse, Austria, and was an important breeding site for amphibians until the lake was stocked with fish in the late 1970s. Salmonids were eradicated in 2005, but the lake remained degraded by the introduced minnows (Phoxinus sp.). In 2018, the lake was drained through a siphon pipe and then by pumping out water with dirt water pumps. The deepest part was treated with slaked lime, but several hundred adult minnows survived in sediment crevices and reproduced in the following season. After drainage, the phytoplankton biomass increased. Indicator species, such as Daphnia longispina and amphibians, showed signs of recovery, but they went back to an impacted state when minnows recovered after the failed eradication attempt. Purse seines proved to be the most efficient gear to catch minnows. These results indicate that deep mountain lakes are difficult to drain efficiently. Sediment treatment is required to eliminate all fish.

In response to the current worldwide amphibian extinction crisis, conservation instances have encouraged the establishment of ex-situ collections for endangered species. The resulting assurance populations are managed under strict biosecure protocols, often involving artificial cycles of temperature and humidity to induce active and overwintering phases, which likely affect the bacterial symbionts living on the amphibian skin. However, the skin microbiota is an important first line of defense against pathogens that can cause amphibian declines, such as the chytrid Batrachochytrium dendrobatidis (Bd). Determining whether current husbandry practices for assurance populations might deplete amphibians from their symbionts is therefore essential to conservation success. Here, we characterize the effect of the transitions from the wild to captivity, and between aquatic and overwintering phases, on the skin microbiota of two newt species. While our results confirm differential selectivity of skin microbiota between species, they underscore that captivity and phase-shifts similarly affect their community structure. More specifically, the translocation ex-situ is associated with rapid impoverishment, decrease in alpha diversity and strong species turnover of bacterial communities. Shifts between active and overwintering phases also cause changes in the diversity and composition of the microbiota, and on the prevalence of Bd-inhibitory phylotypes. Altogether, our results suggest that current husbandry practices strongly restructure the amphibian skin microbiota. Although it remains to be determined whether these changes are reversible or have deleterious effects on their hosts, we discuss methods to limit microbial diversity loss ex-situ and emphasize the importance of integrating bacterial communities to applied amphibian conservation.

The key role of symbiotic skin bacteria communities in amphibian resistance to emerging pathogens is well recognized, but factors leading to their dysbiosis are not fully understood. In particular, the potential effects of population translocations on the composition and diversity of hosts' skin microbiota have received little attention, although such transfers are widely carried out as a strategy for amphibian conservation. To characterize the potential reorganization of the microbiota over such a sudden environmental change, we conducted a common-garden experiment simulating reciprocal translocations of yellow-spotted salamander larvae across three lakes. We sequenced skin microbiota samples collected before and 15 days after the transfer. Using a database of antifungal isolates, we identified symbionts with known function against the pathogen Batrachochytrium dendrobatidis, a major driver of amphibian declines. Our results indicate an important reorganization of bacterial assemblages throughout ontogeny, with strong changes in composition, diversity and structure of the skin microbiota in both control and translocated individuals over the 15 days of monitoring. Unexpectedly, the diversity and community structure of the microbiota were not significantly affected by the translocation event, thus suggesting a strong resilience of skin bacterial communities to environmental change-at least across the time-window studied here. A few phylotypes were more abundant in the microbiota of translocated larvae, but no differences were found among pathogen-inhibiting symbionts. Taken together, our results support amphibian translocations as a promising strategy for this endangered animal class, with limited impact on their skin microbiota.