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The salamander chytrid fungus (Batrachochytrium salamandrivorans [Bsal]) is causing massive mortality of salamanders in Europe. The potential for spread via international trade into North America and the high diversity of salamanders has catalyzed concern about Bsal in the U.S. Surveillance programs for invading pathogens must initially meet challenges that include low rates of occurrence on the landscape, low prevalence at a site, and imperfect detection of the diagnostic tests. We implemented a large-scale survey to determine if Bsal was present in North America designed to target taxa and localities where Bsal was determined highest risk to be present based on species susceptibility and geography. Our analysis included a Bayesian model to estimate the probability of occurrence of Bsal given our prior knowledge of the occurrence and prevalence of the pathogen. We failed to detect Bsal in any of 11,189 samples from 594 sites in 223 counties within 35 U.S. states and one site in Mexico. Our modeling indicates that Bsal is highly unlikely to occur within wild amphibians in the U.S. and suggests that the best proactive response is to continue mitigation efforts against the introduction and establishment of the disease and to develop plans to reduce impacts should Bsal establish.

Testing for intraspecific variation for host tolerance or resistance in wild populations is important for informing conservation decisions about captive breeding, translocation, and disease treatment. Here, we test the importance of tolerance and resistance in multiple populations of boreal toads (Anaxyrus boreas boreas) against Batrachochytrium dendrobatidis (Bd), the amphibian fungal pathogen responsible for the greatest host biodiversity loss due to disease. Boreal toads have severely declined in Colorado (CO) due to Bd, but toad populations challenged with Bd in western Wyoming (WY) appear to be less affected. We used a common garden infection experiment to expose post‐metamorphic toads sourced from four populations (2 in CO and 2 in WY) to Bd and monitored changes in mass, pathogen burden and survival for 8 weeks. We used a multi‐state modelling approach to estimate weekly survival and transition probabilities between infected and cleared states, reflecting a dynamic infection process that traditional approaches fail to capture. We found that WY boreal toads are more tolerant to Bd infection with higher survival probabilities than those in CO when infected with identical pathogen burdens. WY toads also appeared more resistant to Bd with a higher probability of infection clearance and an average of 5 days longer to reach peak infection burdens. Our results demonstrate strong intraspecific differences in tolerance and resistance that likely contribute to why population declines vary regionally across this species. Our multi‐state framework allowed us to gain inference on typically hidden disease processes when testing for host tolerance or resistance. Our findings demonstrate that describing an entire host species as ‘tolerant’ or ‘resistant’ (or lack thereof) is unwise without testing for intraspecific variation. [ABSTRACT FROM AUTHOR]

The metapopulation concept has far-reaching implications in ecology and conservation biology. Hanski's criteria operationally define metapopulations, yet testing them is hindered by logistical and financial constraints inherent to the collection of long-term demographic data. Hence, ecologists and conservationists often assume metapopulation existence for dispersal-limited species that occupy patchy habitats. To advance understanding of metapopulation theory and improve conservation of metapopulations, we used population and landscape genetic tools to develop a methodological framework for evaluating Hanski's criteria. We used genotypic data (11 microsatellite loci) from a purported metapopulation of Boreal Chorus Frogs (Pseudacris maculata (Agassiz, 1850)) in Colorado, U.S.A., to test Hanski's four criteria. We found support for each criterion: (1) significant genetic differentiation between wetlands, suggesting distinct breeding populations; (2) wetlands had small effective population sizes and recent bottlenecks, suggesting populations do not experience long-term persistence; (3) population graphs provided evidence of gene flow between patches, indicating potential for recolonization; and (4) multiscale bottleneck analyses suggest asynchrony, indicating that simultaneous extinction of all populations was unlikely. Our methodological framework provides a logistically and financially feasible alternative to long-term demographic data for identifying amphibian metapopulations. Key words: Boreal Chorus Frog, Pseudacris maculata, dispersal, functional connectivity, genetic bottleneck, genetic diversity, metapopulations, population graph. Le concept de métapopulation a de vastes applications en écologie et en biologie de la conservation. Si les critères de Hanski définissent les métapopulations sur le plan opérationnel, des contraintes logistiques et financières inhérentes à la collecte de données démographiques de longue durée font entrave à la validation de ces critères. Les écologistes et les conservationnistes partent donc souvent du principe de l'existence de métapopulations pour des espèces à dispersion restreinte qui occupent des habitats parcellaires. Afin de parfaire la compréhension de la théorie des métapopulations et améliorer la conservation des métapopulations, nous avons utilisé des outils génétiques associés aux populations et au paysage pour élaborer un cadre méthodologique pour l'évaluation des critères de Hanski. Nous avons utilisé des données génotypiques (11 sites microsatellites) issues d'une métapopulation présumée de rainettes faux-grillons boréales (Pseudacris maculata (Agassiz, 1850)) au Colorado (États-Unis) pour valider les quatre critères de Hanski. Nos constatations appuient les quatre critères, comme suit: (1) une différenciation génétique significative entre les différents milieux humides indiquerait des populations reproductrices distinctes; (2) les populations des milieux humides étaient de petites tailles effectives et caractérisées par des goulots d'étranglement récents, ce qui indiquerait l'absence de persistance à long terme des populations; (3) les graphes de population montrent des indices de flux génique entre les parcelles, ce qui indique un potentiel de recolonisation; et (4) des analyses multi-échelles des goulots d'étranglement semblent témoigner d'une asynchronie, ce qui indique qu'une extinction simultanée de toutes les populations était peu probable. Notre cadre méthodologique constitue une option de rechange viable sur le plan logistique et financier aux données démographiques de longue durée pour l'identification de métapopulations d'amphibiens. [Traduit par la Rédaction] Mots-clés: rainette faux-grillon boréale, Pseudacris maculata, dispersion, connectivité fonctionnelle, goulot d'étranglement génétique, diversité génétique, métapopulations, graphe de population., Introduction Pond-breeding amphibians provide classical examples of metapopulations (Marsh and Trenham 2001; Smith and Green 2006; Semlitsch 2008; Griffiths et al. 2010). Nevertheless, metapopulation dynamics are typically assumed rather than [...]

Abstract Background Rescuing amphibian diversity is an achievable conservation challenge. Disease mitigation is one essential component of population management. Here we assess existing disease mitigation strategies, some in early experimental stages, which focus on the globally emerging chytrid fungus Batrachochytrium dendrobatidis. We discuss the precedent for each strategy in systems ranging from agriculture to human medicine, and the outlook for each strategy in terms of research needs and long-term potential. Results We find that the effects of exposure to Batrachochytrium dendrobatidis occur on a spectrum from transient commensal to lethal pathogen. Management priorities are divided between (1) halting pathogen spread and developing survival assurance colonies, and (2) prophylactic or remedial disease treatment. Epidemiological models of chytridiomycosis suggest that mitigation strategies can control disease without eliminating the pathogen. Ecological ethics guide wildlife disease research, but several ethical questions remain for managing disease in the field. Conclusions Because sustainable conservation of amphibians in nature is dependent on long-term population persistence and co-evolution with potentially lethal pathogens, we suggest that disease mitigation not focus exclusively on the elimination or containment of the pathogen, or on the captive breeding of amphibian hosts. Rather, successful disease mitigation must be context specific with epidemiologically informed strategies to manage already infected populations by decreasing pathogenicity and host susceptibility. We propose population level treatments based on three steps: first, identify mechanisms of disease suppression; second, parameterize epizootiological models of disease and population dynamics for testing under semi-natural conditions; and third, begin a process of adaptive management in field trials with natural populations.

Interventions of the host–pathogen dynamics provide strong tests of relationships, yet they are still rarely applied across multiple populations. After American bullfrogs (Rana catesbeiana) invaded a wildlife refuge where federally threatened Chiricahua leopard frogs (R. chiricahuensis) were reintroduced 12 years prior, managers launched a landscape‐scale eradication effort to help ensure continued recovery of the native species. We used a before‐after‐control‐impact design and environmental DNA sampling of 19 eradication sites and 18 control sites between fall 2016 and winter 2020–2021 to measure community‐level responses to bullfrog eradication, including for two pathogens. Dynamic occupancy models revealed successful eradication from 94% of treatment sites. Native amphibians did not respond to bullfrog eradication, but the pathogens amphibian chytrid fungus (Batrachochytrium dendrobatidis) and ranaviruses were coextirpated with bullfrogs. Our spatially replicated experimental approach provides strong evidence that management of invasive species can simultaneously reduce predation and disease risk for imperiled species. [ABSTRACT FROM AUTHOR]