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Hybridization between the European smooth and palmate newts has recurrently been mentioned in the literature. The only two studies that attempted to quantify the frequency of hybridization and gene admixture between these two species came to strikingly opposite conclusions. According to Arntzen et al. (1998, 42 allozymes), hybrids are rare in nature and introgression negligible, while according to Johanet et al. (2011, 6 microsatellites), introgressive hybridization is significant and widespread across the shared distribution range. To clarify this question, we implemented high-throughput SNP genotyping with diagnostic biallelic SNPs on 965 specimens sampled across Europe. Our results are in line with Arntzen et al., since only two F1 hybrids were identified in two distinct French localities, and no further hybrid generations or backcrosses. Moreover, reanalysis of 78 of the samples previously studied by Johanet et al. (2011) using our SNPs panel could not reproduce their results, suggesting that microsatellite-based inference overestimated the hybridization frequency between these two species. Since we did not detect methodological issues with the analyses of Johanet et al., our results suggest that SNP approaches outperform microsatellite-based assessments of hybridization frequency, and that conclusions previously published on this topic with a small number of microsatellite loci should be taken with caution, and ideally be repeated with an increased genomic coverage.

Quaternary glacial cycles have been key drivers of diversification for Holarctic species, promoting divergence, isolation, and extinction processes in numerous taxa. These cycles facilitated evolutionary radiations in some groups but also erased much of the evolutionary history of species with northern origins. Here, we investigate the evolutionary and phylogeographic history of the Palmate Newt (Lissotriton helveticus), a widespread species in post‐glacial ecosystems in Western Europe. We generate genome‐wide ddRADseq for 205 individuals from 51 populations across the species range and reconstruct its phylogeographic and demographic history, assess population structure, and characterize ecological paleoniches for the species at different climatic periods. Results identify several distinct lineages exhibiting strong genetic differentiation, primarily driven by geographic barriers and isolation in historical refugia with admixture in transition zones. Phylogeographic reconstructions suggest that the main glacial refugium for L. helveticus was most likely located in northern Iberia. Two main dispersal routes were identified: one extending eastward through the Ebro River Basin and a second, following a northeastward pathway across the Pyrenees and into Europe. We specifically pinpoint the origin of Europe's recolonization route to a specific set of localities surrounding Andorra, where L. helveticus probably expanded along tributaries to the Garonne River into southern and western France over warm periods. By integrating genomic, geographic, and paleoclimatic data, this study provides an in‐depth understanding of how climate shaped the evolutionary history of this temperate species and reinforces the importance of waterways for amphibian dispersal dynamics. This study investigates the evolutionary and biogeographic history of the palmate newt (Lissotriton helveticus) by generating a genomic dataset from over 200 specimens across the entire distribution range of the species.

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.

Dispersal is one of the main processes that determine community structure. Individuals make dispersal decisions according to environmental and/or social cues that reflect the fitness prospects in a given patch. The presence and abundance of heterospecifics within the same ecological guild, and/or their breeding success, may act as public information that influences movement decisions. To date, most studies investigating the role of heterospecific attraction have focused on habitat choice, using both experimental and correlational approaches. The present study is the first to examine how long-term variation in heterospecific density in breeding patches may affect dispersal patterns in spatially structured populations. We investigate how the dispersal decisions of the great crested newt (Triturus cristatus) are related to the variable density of two other newt species, the alpine newt (Ichthyosaura alpestris) and the palmate newt (Lissotriton helveticus). To examine this issue, we used capture–recapture data collected in an experimental pond network over a 20-year period. The results revealed that the great crested newt’s dispersal is context dependent and is affected by variation in heterospecific density: individuals were less likely to emigrate from ponds with high heterospecific density and were more likely to immigrate to ponds with high heterospecific density. These findings suggest that individuals adjust their dispersal decisions at least partly based on public information provided by heterospecifics. This mechanism may play a critical role in the dynamics of spatially structured populations and community functioning.

Designing effective conservation plans to protect species from extinction requires a comprehensive understanding of their ecology. Conventional methods used to investigate habitat use are time‐consuming, and the detectability of cryptic species is often insufficient. Environmental DNA (eDNA)‐based approaches provide a complementary tool to traditional monitoring methods for ecosystem monitoring and assessment. Nevertheless, to our knowledge, such methods have rarely been applied to investigate habitat use at a fine scale in a continuous wetland environment. Here, we used an eDNA metabarcoding approach to characterize the breeding habitat use of local amphibian species in a wet meadow expanse along the southern shore of Lake Neuchâtel, Switzerland. We retrieved DNA from six out of the seven species expected to be present. We tested the influence of six abiotic environmental variables on overall species assemblages and individual species occurrences. We showed that the main factor structuring species assemblages was water temperature and that the distribution of three amphibian species was associated with several environmental variables. Our results indicate that the eDNA detection approaches are promising tools to study species' ecology at a small scale in continuous wetland habitats. Understanding species ecology is essential for effective conservation, but conventional monitoring techniques often lack efficiency and detectability, particularly for cryptic species. Using environmental DNA (eDNA) metabarcoding in conjunction with habitat characterization, we found six out of seven expected amphibian species in a wet meadow expanse and highlighted water temperature as a key factor shaping species assemblages. The results demonstrate that eDNA detection methods are promising tools for small‐scale ecological studies in continuous wetland habitats.

Emerging infectious diseases represent a key problem for the survival of amphibian populations. Declines related to infections of the chytrid fungus Batrachochytrium dendrobatidis and Ranavirus have been described in several areas of Northern Spain, including protected areas. Co-infection—the simultaneous infection of a host by multiple pathogen species—can increase the susceptibility to subsequent infections. Here, we describe a case of triple dermocystid-ranavirus-chytrid fungus co-infection in a specimen of palmate newt (Lissotriton helveticus) from a protected wetland of North-western Spain. Five palmate newts and one Bosca’s newt (Lissotriton boscai) were found dead, and tissue samples were analysed by using qPCR methods. Ranavirus was detected in four out of five L. helveticus and in the L. boscai individual, whereas Bd was detected only in one of the five L. helveticus. Four out of six specimens tested positive for Dermocystidium. Sequencing was performed to double-check the presence of Dermocystidium in a qPCR-positive sample for that pathogen.

Efficient delineation of conservation areas is a great challenge in maintaining biodiversity. Kernel density estimators (KDEs) are a powerful tool in this perspective, but they have not been applied at the population level on patch-distributed organisms. This would be particularly worthy for species that need broad habitats beyond those where they can be sampled; such as terrestrial lands for pond-breeding amphibians. The aim of this study was to compare different approaches for the identification of suitable areas for conservation: KDE, ecological niche modelling, and a combination of KDE and niche models. Paedomorphosis was chosen as a model system because this is an important form of intraspecific variation that is present in numerous taxa, but geographically localized within species and globally endangered. 277 ponds were sampled in one of the hotspots of paedomorphosis to determine the abundance and distribution of paedomorphs (i.e., individuals retaining gills at the adult stage) of the palmate newt ( Lissotriton helveticus ), with emphasis on the connections between the most valuable populations. KDEs gave insights into the surface areas required to balance the maintenance of certain number of connected ponds and the respective number of disjoint areas in which the whole population is divided. The inclusion of barriers in the models helped in accurately designing the limits of the areas to protect. Alone, habitat models were not able to successfully delineate the area to protect, but the integration between terrestrial suitable areas or barriers and KDE allowed an objective identification of areas required for conservation. Overall, the best performance was observed by the KDE integrating ecological barriers, and by the combination between KDE and niche modelling. In a broader perspective, KDEs are thus a pertinent tool in providing quantitative spatial measurements to delineate conservation areas based on patch-abundance data with a specific focus to connectivity.

Does urbanization affect key life-history traits in native organisms? Some studies show that urban areas reduce diversity in certain taxa, but there is little insight into how these environments affect physiological and ecological traits. Urban areas have distinct physical structure and ecological processes compared to original habitats. The environmental changes associated with urban areas can influence the costs and benefits of different traits and behaviors of local organisms. Some of these effects have been explored in groups such as birds, but we might expect stronger effects in animals with reduced mobility, such as amphibians. Importantly, the effects of urban habitats on amphibians have not been explored, in spite that these are the most threatened vertebrate group in the world. Here, we compared three main traits related to the fitness of amphibians in urban and natural habitats: body size, body condition and immune response. To test the generality of our results, we assessed adult males of four amphibian species. We found that the body size was larger in urban environment populations in three of four studied species, while the body condition was better in the urban populations of two aquatic newt species. Finally, we found no effect of urbanization on the immune response of individuals of any species. In conclusion, we show that different species of amphibians may be affected differently by anthropogenic habitat alteration depending on their specific ecology.

Heterochrony, the change in the rate or timing of development between ancestors and their descendants, plays a major role in evolution. When heterochrony produces polymorphisms, it offers the possibility to test hypotheses that could explain its success across environments. Amphibians are particularly suitable to exploring these questions because they express complex life cycles (i.e. metamorphosis) that have been disrupted by heterochronic processes (paedomorphosis: retention of larval traits in adults). The large phenotypic variation across populations suggests that more complex processes than expected are operating, but they remain to be investigated through multivariate analyses over a large range of natural populations across time. In this study, we compared the likelihood of multiple potential environmental determinants of heterochrony. We gathered data on the proportion of paedomorphic and metamorphic palmate newts (Lissotriton helveticus) across more than 150 populations during 10 years and used an information‐theoretic approach to compare the support of multiple potential processes. Six environmental processes jointly explained the proportion of paedomorphs in populations: predation, water availability, dispersal limitation, aquatic breathing, terrestrial habitat suitability and antipredator refuges. Analyses of variation across space and time supported models based on the advantage of paedomorphosis in favourable aquatic habitats. Paedomorphs were favoured in deep ponds, in conditions favourable to aquatic breathing (high oxygen content), with lack of fish and surrounded by suitable terrestrial habitat. Metamorphs were favoured by banks allowing easy dispersal. These results indicate that heterochrony relies on complex processes involving multiple ecological variables and exemplifies why heterochronic patterns occur in contrasted environments. On the other hand, the fast selection of alternative morphs shows that metamorphosis and paedomorphosis developmental modes could be easily disrupted in natural populations.

Paedomorphosis is a major evolutionary process that bypasses metamorphosis and allows reproduction in larvae. In newts and salamanders, it can be facultative with paedomorphs retaining gills and metamorphs dispersing. The evolution of these developmental processes is thought to have been driven by the costs and benefits of inhabiting aquatic versus terrestrial habitats. In this context, we aimed at testing the hypothesis that climatic drivers affect phenotypic transition and the difference across sexes because sex-ratio is biased in natural populations. Through a replicated laboratory experiment, we showed that paedomorphic palmate newts (Lissotriton helveticus) metamorphosed at a higher frequency when water availability decreased and metamorphosed earlier when temperature increased in these conditions. All responses were sex-biased, and males were more prone to change phenotype than females. Our work shows how climatic variables can affect facultative paedomorphosis and support theoretical models predicting life on land instead of in water. Moreover, because males metamorphose and leave water more often and earlier than females, these results, for the first time, give an experimental explanation for the rarity of male paedomorphosis (the ‘male escape hypothesis’) and suggest the importance of sex in the evolution of paedomorphosis versus metamorphosis.