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Chytridiomycosis is affecting hundreds of amphibian species worldwide, but while in tropical areas, adult individuals have been the focus of most investigations, the exact role played by infection intensity of breeding adults is not well understood in temperate areas. We conducted mark-recapture-capture surveys during spiny common toad breeding seasons from 2006 to 2018 at the site of the first recorded outbreak of chytridiomycosis in Europe, the Peñalara Massif (Sierra de Guadarrama National Park, central Spain), and collected infection samples and several variables related to the reproductive effort of male individuals. We used general linear mixed models to evaluate the contribution of study variables on the infection loads of adult male toads exhibited at their capturing date. We also analysed the differences on several male characteristics between the pond with the largest breeding population against the rest of the ponds. We found that the duration of time spent in the waterbody and the condition of the host predicted infection loads. Animals of good physical condition, that spent longer in water, have higher infection levels than individuals with the opposite set of traits. The pond supporting the largest breeding population housed smaller male toads and in poorer condition. Our results are consistent with a shift in reproductive strategy in response to infection and potentially a strategy of tolerance, rather than resistance to infection. These findings have applications for disease mitigation and theoretical implications related to the trade-offs made and the evolution of traits in response to the disease., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This study was funded by Organismo Autónomo Parques Nacionales of Spain (Project Ref. 2399/2017, PI: JBo). BT was supported by ‘Doctorados Industriales de la Comunidad de Madrid’ (Ref. IND2020/AMB-17438).

In 2020 and 2021 we detected in Catalonia (NE Spain) six new episodes of mortality or presence of dying specimens in introduced Mediterranean painted frogs (Discoglossus pictus). All affected individuals were positive to the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). Histological examinations showed intense involvement of the superficial layers of the epidermis and qPCR analyses yielded infection loads greater than 100 000 genomic equivalents of zoospores. These results suggest that this introduced species could behave as a Bd ‘supershedder’, and recommend to control its expansion due to its important role in the dynamic of chytridiomycosis.

Los anfibios son los vertebrados más amenazados. Las enfermedades emergentes de los anfibios, como la quitridiomicosis y ranavirosis, constituyen una de sus amenazas más relevantes, causando mortalidades masivas, declives poblacionales y extinciones. Dada la preocupación internacional por la crisis de los anfibios, en las últimas décadas han surgido muchas iniciativas para el seguimiento de poblaciones. Desgraciadamente, muchas de estas iniciativas no resultan eficaces para determinar la emergencia de estas enfermedades ni para evaluar su impacto real en las poblaciones, dado que: no se centran en las especies, los estadios de desarrollo y las épocas del año adecuadas, y no incluyen la toma de datos de infección de manera regular. En el caso de las poblaciones con incidencia de patógenos conocida la situación no es mejor, dado que raramente se llevan a cabo programas de seguimiento a largo plazo una vez que los brotes de mortalidad han cesado. Por lo tanto, mientras que cada vez son más frecuentes los casos publicados de mortalidades masivas de anfibios asociados a las enfermedades emergentes, existe un vacío de conocimiento significativo sobre la incidencia real de estas enfermedades y de sus efectos a medio y largo plazo.

We report the first cases of mortality in anurans associated with the presence of the fungus Batrachochytrium dendrobatidis at four different localities from Catalonia (NE Iberian Peninsula, Spain). All cases were confirmed by both molecular techniques and histology. The infected individuals were two Mediterranean painted frogs (Discoglossus pictus) from Girona province found in 2018 and 2020, one Iberian waterfrog (Pelophylax perezi) from Tarragona province found in 2018, and one European common frog (Rana temporaria) from Barcelona province found in 2019. This is the first time that mortality associated with this pathogen has been confirmed in D. pictus and P. perezi. The role of the fungus as an agent possibly leading to death, in association with other external environmental factors, is discussed. These findings could suggest a recent increase of the incidence of this disease in the region. Some of these cases are particularly worrying because of their occurrence close to sites where some endemic amphibian species with extremely reduced distributions inhabit.

Considering that emerging infectious diseases are one of the major drivers of global amphibian decline, controlling the spread of infections are evenmore challenging. Amphibian skin disease chytridiomycosis, which is caused by two species of fungi belonging to the Batrachochytrium genus, has been detected in at least 700 amphibian species causingmass mortalities in all continents where amphibian soccur. Most Alytes species, including the Beticmid wife toad (A. dickhilleni), are highly susceptible to B. dendrobatidis(Bd) with lethal consequences. The presence of Bd infection in A. dickhilleni was confirmed ten years ago in just three localities across the entire distribution range of this threatened species. Here we report the extraordinary Bd expansion through the entire distribution range of A. dickhilleniand analyse if former infected populations acted as the source of transmission events to current infected populations. Currently,Bd infection is broadly distributed across the entire distribution range of the species and the increase of infection prevalence reached 30–50% during a decade. The populations where the infection was detected a decade ago could be identified as likely sources of infection for somelocations where the pathogen is now present. The introduction of infected amphibian hosts into previously naïve A. dickhilleni breeding sites, and otheranthropogenic processes, are seeming to be the most plausible way of Bd range expansion, motivating mass mortalities, population declines and extirpation events of this threatened amphibian species., This work was funded by the Consejería de Medio Ambiente of Junta de Andalucía (Contract Number NET378406/1).

Chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal), has had an unprecedented impact on amphibian biodiversity. Although Bd is globally widespread, Bsal is currently spreading, increasing the probability that these pathogens will co-occur in individual amphibians. Interactions among coinfecting parasites can have significant outcomes on disease dynamics and impact and, therefore, may have important consequences for amphibian conservation. We analyzed the patterns of Bd-Bsal coinfections in two species of free-ranging urodeles during an outbreak of chytridiomycosis in Spain. Our goals were to assess 1) the probability of co-occurrence of both chytrid species and 2) the correlation of pathogen loads in coinfected hosts. We detected coinfections in 81.58% of Triturus marmoratus (n=38) and in 18.75% of Ichthyosaura alpestris (n=16). Histopathologic lesions of chytridiomycosis were observed only in T. marmoratus. Our results demonstrate a positive relationship between Bd and Bsal loads in T. marmoratus, whereas the co-occurrence analysis showed a random association among pathogens in both urodele species. Overall, we show that Bd-Bsal coinfections intensify pathogen load in T. marmoratus and could, therefore, increase disease severity and have important consequences for the conservation of some amphibian species.

Multiple threats, including emerging infectious diseases, are contributing to the extinction of amphibians worldwide. One of the most devastating diseases is the fatal amphibian skin disease chytridiomycosis caused by the fungus Batrachochytrium dendrobatidis (Bd). The presence of Bd in North Africa was described in 2011 and this included the distribution range of the endemic Moroccan midwife toad (Alytes maurus). Here we report new Bd positive occurrences across several distant regions of Morocco, augment the known number of infected species, and describe the first evidence of lethal chytridiomycosis in A. maurus. Although population declines in this species were not recorded, the family Alytidae has been identified as the most susceptible taxonomic group to chytridiomycosis of the Palearctic. An environmental niche model, taking into account new records of Bd in the country, confirms the Mediterranean coast and the Rif and Middle Atlas Mountains as very favourable areas for Bd. Our results suggest that the real impact of chytridiomycosis in North Africa is poorly understood, and that this continent cannot be identified as a region less impacted by chytridiomycosis, as was previously proposed.

Microplastics (MPs), a new class of pollutants that pose a threat to aquatic biodiversity, are of increasing global concern. In tandem, the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) causing the disease chytridiomycosis is emerging worldwide as a major stressor to amphibians. We here assess whether synergies exist between this infectious disease and MP pollution by mimicking natural contact of a highly susceptible species (midwife toads, Alytes obstetricans) with a Bd-infected reservoir species (fire salamanders, Salamandra salamandra) in the presence and absence of MPs. We found that MP ingestion increases the burden of infection by Bd in a dose‑dependent manner. However, MPs accumulated to a greater extent in amphibians that were not exposed to Bd, likely due to Bd‑damaged tadpole mouthparts interfering with MP ingestion. Our experimental approach showed compelling interactions between two emergent processes, chytridiomycosis and MP pollution, necessitating further research into potential synergies between these biotic and abiotic threats to amphibians., This study was funded by the Spanish Ministry for Science, Innovation and Universities (BioLoss project, Ref. RTI2018-095023-B-I00) and the Basque Government (Ref. IT951-16). MCF is funded by the UK Natural Envi- ronmental Research Council NERC NE/S000992/1 and is a fellow in the Canadian CIFAR program.

The number of epizootics in amphibian populations caused by viruses of the genus Ranavirus is increasing worldwide. Yet, causes for pathogen emergence are poorly understood. Here, we confirmed that the Common midwife toad virus (CMTV) and Frog virus 3 (FV3) are responsible for mass mortalities in Iberia since the late 1980s. Our results illustrate the Iberian Peninsula as a diversity hotspot for the highly virulent CMTV. Although this pattern of diversity in Europe is consistent with spread by natural dispersal, the exact origin of the emergence of CMTV remains uncertain. Nevertheless, our data allow hypothesizing that the Iberian Peninsula might harbor the ancestral population of CMTVs that could have spread into the rest of Europe. In addition, we found that climate warming could be triggering the CMTV outbreaks, supporting its endemic status in the Iberian Peninsula., This work was supported by Organismo Autónomo Parques Nacionales of Spain (ref. 2399/2017; PI: JB), Foundation for the Conservation of Salamanders (project ‘‘Monitoring the incidence of emerging pathogens on endemic urodeles from the Cantabrian range, Spain’’; PI: BT), and Fundaçao para a Ciencia e a Tecnologia (Ref. PTDC/BIA-CBI/2434/2021; PI: GMR,Co-PI: JB).

The recent introduction of the chytrid fungus Batrachochytrium salamandrivorans into north-eastern Spain threatens salamander diversity on the Iberian Peninsula. We assessed the current epidemiological situation with extensive field sampling of urodele populations. We then sought to delineate priority regions and identify conservation units for the Iberian Peninsula by estimating the susceptibility of Iberian urodeles using laboratory experiments, evidence from mortality events in nature and captivity and inference from phylogeny. None of the 1395 field samples, collected between 2015 and 2021 were positive for Bsal and no Bsal-associated mortality events were recorded, in contrast to the confirmed occurrence of Bsal outbreak previously described in 2018. We classified five of eleven Iberian urodele species as highly susceptible, predicting elevated mortality and population declines following potential Bsal emergence in the wild, five species as intermediately susceptible with variable disease outcomes and one species as resistant to disease and mortality. We identified the six conservation units (i.e., species or lineages within species) at highest risk and propose priority areas for active disease surveillance and field biosecurity measures. The magnitude of the disease threat identified here emphasizes the need for region-tailored disease abatement plans that couple active disease surveillance to rapid and drastic actions., This research was funded by the European Commission (Tender ENV.B.3/SER/2016/0028, Mitigating a new infectious disease in salamanders to counteract the loss of biodiversity), the Foundation for the Conservation of Salamanders (project “Monitoring the incidence of emerging pathogens on endemic urodeles from the Cantabrian range, Spain”). B.T. was supported by a ‘Doctorados Industriales’ grant of Comunidad de Madrid, Spain (ref. IND2020/AMB-17438). G.V.-A. was financed by the Portuguese Foundation for Science and Technology (FCT; CEECIND/00937/2018). B.C.S. was supported by an ARC DECRA (DE200100121).

Amphibians are the most highly threatened vertebrates, and emerging pathogens are a serious threat to their conservation. Amphibian chytrid fungi and the viruses of the Ranavirus genus are causing disease outbreaks worldwide, including in protected areas such as National Parks. However, we lack information about their effect over amphibian populations in the long-term, and sometimes these mortality episodes are considered as transient events without serious consequences over longer time-spans. Here, we relate the occurrence of both pathogens with the population trends of 24 amphibian populations at 15 sites across a national Park in northern Spain over a 14-year period. Just one out 24 populations presents a positive population trend being free of both pathogens, while seven populations exposed to one or two pathogens experienced strong declines during the study period. The rest of the study populations (16) remain stable, and these tend to be of species that are not susceptible to the pathogen present or are free of pathogens. Our study is consistent with infectious diseases playing an important role in dictating amphibian population trends and emphasizes the need to adopt measures to control these pathogens in nature. We highlight that sites housing species carrying Ranavirus seems to have experienced more severe population-level effects compared to those with the amphibian chytrid fungus, and that ranaviruses could be just as, or more important, other more high-profile amphibian emerging pathogens., This study was funded by the Spanish Ministry for Science, Innovation and Universities (CGL2015-70070-R, PI: JBo and RTI2018-095023-B-I00, PI: Luz Boyero) and by Organismo Autónomo Parques Nacionales of Spain (2399/2017, PI: JBo).We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

Coping with anthropogenic environmental change is among the greatest challenges faced by wildlife, and endocrine flexibility is a potentially crucial coping mechanism. Animals may adapt to anthropogenic environments by dampening their glucocorticoid stress response, but empirical tests of this hypothesis have provided mixed evidence. An alternative hypothesis is that a non-attenuated stress response and efficient negative feedback are favored in anthropogenic habitats. To test this idea, we non-invasively sampled corticosterone release rates of common toad (Bufo bufo) tadpoles in agricultural, urban, and natural habitats, and quantified their stress response and negative feedback by a standardized stress-and-recovery protocol. We repeated the same sampling with tadpoles raised from eggs from the same ponds in a common-garden experiment to infer if the differences observed between populations in different habitats were due to individual phenotypic plasticity rather than microevolution or transgenerational effects. We found that, compared to tadpoles in natural ponds, urban tadpoles had higher baseline and stressed corticosterone release rates, and tadpoles in agricultural ponds had similar corticosterone release rates but greater stress-induced change, indicating stronger stress responses in both types of anthropogenic habitats. As predicted, tadpoles in both agricultural and urban ponds showed more efficient negative feedback than did tadpoles in natural ponds. Water pollution levels, as indicated by the concentrations of carbamazepine and corticoid-disrupting compounds in pond water, contributed to elevating the stress response regardless of land use. Infection by neither Batrachochytrium dendrobatidis nor Ranavirus was detected in free-living tadpoles. No habitat-related glucocorticoid differences persisted in the common-garden experiment. These results suggest that toad tadpoles in anthropogenic habitats increased their glucocorticoid flexibility via phenotypic plasticity. The coupling of stronger stress response and stronger negative feedback in these habitats supports the importance of rapidly “turning on and off” the stress response as a mechanism for coping with anthropogenic environmental change., The study was supported by a Fulbright Research Grant to CRG, and by the NRDI Fund of the National Research, Development and Innovation Office of Hungary (grants "OTKA"-115402 and 2019-2.1.11-TÉT2019-00026 to VB). GINOP-2.3.3-15-2016-00018 supported the UPLCMS/MS analysis.

Emerging infectious diseases are a threat to biodiversity and have taken a large toll on amphibian populations worldwide. The chytrid fungi Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal), and the iridovirus Ranavirus (Rv), are of concern as all have contributed to amphibian declines. In central and eastern Europe, their geographical and host distributions and main environmental drivers determining prevalence are poorly known. We screened over 1000 amphibians from natural and captive populations in Poland for the presence of Bd, Bsal and Rv. In wild amphibian populations, we found that Bd is widespread, present in 46 out of 115 sampled localities as well as 2 captive colonies, and relatively common with overall prevalence at 14.4% in 9 species. We found lower prevalence of Rv at 2.4%, present in 11 out of 92 sampling sites, with a taxonomic breadth of 8 different amphibian species. Bsal infection was not detected in any individuals. In natural populations, Pelophylax esculentus and Bombina variegata accounted for 75% of all Bd infections, suggesting a major role for these 2 species as pathogen reservoirs in Central European freshwater habitats. General linear models showed that climatic as well as landscape features are associated with Bd infection in Poland. We found that higher average annual temperature constrains Bd infection, while landscapes with numerous water bodies or artificial elements (a surrogate for urbanization) increase the chances of infection. Our results show that a combination of climatic and landscape variables may drive regional and local pathogen emergence.

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.

The distribution of the chytrid fungus Batrachochytrium salamandrivorans continues to expand in Europe. During 2014-2018, we collected 1,135 samples from salamanders and newts in 6 countries in Europe. We identified 5 cases of B. salamandrivorans in a wild population in Spain but none in central Europe or the Balkan Peninsula.