RESUMO

Amphibian populations have been declining worldwide, with global climate changes and infectious diseases being among the primary causes of this scenario. Infectious diseases are among the primary drivers of amphibian declines, including ranavirosis and chytridiomycosis, which have gained more attention lately. While some amphibian populations are led to extinction, others are disease-resistant. Although the host's immune system plays a major role in disease resistance, little is known about the immune mechanisms underlying amphibian disease resistance and host-pathogen interactions. As ectotherms, amphibians are directly subjected to changes in temperature and rainfall, which modulate stress-related physiology, including immunity and pathogen physiology associated with diseases. In this sense, the contexts of stress, disease and ecoimmunology are essential for a better understanding of amphibian immunity. This issue brings details about the ontogeny of the amphibian immune system, including crucial aspects of innate and adaptive immunity and how ontogeny can influence amphibian disease resistance. In addition, the papers in the issue demonstrate an integrated view of the amphibian immune system associated with the influence of stress on immune-endocrine interactions. The collective body of research presented herein can provide valuable insights into the mechanisms underlying disease outcomes in natural populations, particularly in the context of changing environmental conditions. These findings may ultimately enhance our ability to forecast effective conservation strategies for amphibian populations. This article is part of the theme issue 'Amphibian immunity: stress, disease and ecoimmunology'.

Assuntos

RESUMO

Chytridiomycosis is affecting amphibians worldwide, causing the decline and extinction of several amphibian populations. The disease is caused by the fungus Batrachochytrium dendrobatidis (Bd), a multihost pathogen living in freshwater habitats. While several environmental factors have been associated with the prevalence of Bd and its virulence, the effects of water quality on the pathogen are not clear yet. Some evidence suggests that water pollution may reduce amphibians' immune response and increase prevalence of Bd. To explore this hypothesis, we analyzed the relationship between water quality and the presence of Bd by using spatial data mining of 150 geolocations of Bd in amphibians from 9 families where Bd positive specimens have been previously reported, and water quality in 4,202 lentic and lotic water bodies in Mexico from 2010 to 2021. Our model showed that in the 3 main families where Bd was recorded, its presence is high in locations with low water quality, i.e., water polluted likely contaminated with urban and industrial waste. Using this model, we inferred areas suitable for Bd in Mexico; mainly in poorly studied areas along the gulf and on the pacific slope. We further argue that actions to reduce water pollution should become an integral part of public policies to prevent the spread of Bd and protect amphibians from this deadly pathogen.

Assuntos

RESUMO

Based on morphological and molecular characters, we describe a new species of terrestrial breeding frog of the Pristimantisdanae Group from montane forests of La Mar Province, Ayacucho Department in southern Peru, at elevations from 1200 to 2000 m a.s.l. The phylogenetic analysis, based on concatenated sequences of gene fragments of 16S rRNA, RAG1, COI and TYR suggests that the new species is a sister taxon of a clade that includes one undescribed species of Pristimantis from Cusco, Pristimantispharangobates and Pristimantisrhabdolaemus. The new species is most similar to P.rhabdolaemus, which differs by lacking scapular tubercules and by its smaller size (17.0-18.6 mm in males [n = 5], 20.8-25.2 mm in females [n = 5] in the new species vs. 22.8-26.3 mm in males [n = 19], 26.0-31.9 mm in females [n = 30] of P.rhabdolaemus). Additionally, we report the prevalence of Batrachochytriumdendrobatidis (Bd) in this species.

ResumenDescribimos una nueva especie de rana terrestre de desarrollo directo del grupo Pristimantisdanae de bosques montanos procedentes de la provincia de La Mar, departamento de Ayacucho al sur de Perú con rango de distribución altitudinal entre los 1200­2000 msnm, en base a caracteres morfológicos y moleculares. El análisis filogenético basado en las secuencias concatenadas de los fragmentos de genes ARNr 16S, COI, RAG1 y TYR sugiere que la nueva especie es un taxón hermano del clado que incluye a una especie de Pristimantis no descrita de Cusco, Pristimantispharangobates y Pristimantisrhabdolaemus. La nueva especie se asemeja más a P.rhabdolaemus; de la cual difiere por la ausencia de tubérculos escapulares y su menor tamaño corporal (17.0­18.6 mm en machos [n=5], 20.8­25.2 mm en hembras [n=5] en la nueva especie vs 22.8­26.3 mm en machos [n=19], 26.0­31.9 mm en hembras [n=30] de P.rhabdolaemus). Adicionalmente, reportamos la prevalencia de Batrachochytriumdendrobatidis (Bd) en esta especie de Terrarana.

RESUMO

The recent emergence of the pathogen Batrachochytrium salamandrivorans (Bsal) is associated with rapid population declines of salamanders in Europe and its arrival to new areas could cause dramatic negative effects on other amphibian populations and species. Amphibian species, present in areas with high amphibian diversity such as Mexico, could be highly threatened due to the arrival of Bsal, particularly salamander species which are more vulnerable to chytridiomycosis caused by this pathogen. Thus, immediate surveillance is needed as a strategy to efficiently contend with this emerging infectious disease. In this study, we analyzed 490 wild and captive amphibians from 48 species across 76 sites in the North, Central, and South of Mexico to evaluate the presence of Bsal. Amphibians were sampled in sites with variable degrees of amphibian richness and suitability for Bsal according to previous studies. From the 76 sampling sites, 10 of them were located in areas with high amphibian richness and potential moderate to high Bsal habitat suitability. We did not detect Bsal in any of the samples, and no signs of the disease were observed in any individual at the time of sampling. Our results suggest that Bsal has not yet arrived at the sampled sites or could be at low prevalence within populations with low occurrence probability. This is the first study that evaluates the presence of Bsal in different regions and amphibian species in Mexico, which is the second most diverse country in salamander species in the world. We highlight the risk and the importance of continuing surveillance of Bsal in Mexico and discuss control strategies to avoid the introduction and spread of Bsal in the country.

Assuntos

RESUMO

Compensatory recruitment is a key demographic mechanism that has allowed the coexistence of populations of susceptible amphibians with Batrachochytrium dendrobatidis (Bd), a fungus causing one of the most devastating emerging infectious disease ever recorded among vertebrates. However, the underlying processes (e.g. density-dependent increase in survival at early life stages, change in reproductive traits) as well as the level of interpopulation variation in this response are poorly known. We explore potential mechanisms of compensatory recruitment in response to Bd infection by taking advantage of an amphibian system where male reproductive traits are easy to quantify in free-living populations. The Southern Darwin's frog Rhinoderma darwinii is a vocal sac-brooding species that exhibits a high susceptibility to lethal Bd infection. Using a 7-year capture-recapture study at four populations with contrasting Bd infection status (one high prevalence, one low prevalence and two Bd-free populations), we evaluated whether Bd-positive populations exhibited a higher adult recruitment and a higher male reproductive effort than Bd-negative populations. We also estimated population growth rates to explore whether recruitment compensated for the negative impacts of Bd on the survival of adults. In addition, we evaluated a potential demographic signal of compensatory recruitment (i.e. positive relationship between the proportion of juveniles and Bd prevalence) in response to Bd infection using raw count data from 13 R. darwinii populations. The high Bd prevalence population exhibited the highest male reproductive effort and the highest recruitment among the four monitored populations. This led to a growing population during the study period despite high mortality of adult hosts. In contrast, males from the population with low Bd prevalence had a low reproductive effort and this population, which had the lowest adult recruitment, was declining during the study period despite adults having a higher survival in comparison to the high Bd prevalence population. We also found a demographic signal of compensatory recruitment in response to Bd infection in our broader analysis of 13 R. darwinii populations. Our study underlines the importance of interpopulation variation in life-history strategies on the fate of host populations after infectious disease emergence. Our results also suggest that an increase in reproductive effort can be one of the processes underlying compensatory recruitment in populations of Bd-susceptible amphibians.

Assuntos

RESUMO

The skin microbiome in amphibians has gained a lot of attention as some of its members play a protective role against pathogens such as the fungus Batrachochytrium dendrobatidis (Bd). The composition of skin bacterial communities has been suggested as one of the factors explaining differences in susceptibility to Bd among amphibian species and populations. The boreal toad Anaxyrus boreas is known to be susceptible to Bd, and severe population declines in its southeastern range have been documented. However, throughout A. boreas distribution, populations present differences in susceptibility to Bd infections which may be associated with differences in skin microbial diversity. This study compared the skin bacterial diversity and Bd infection levels of A. boreas in one desert population and one pine forest population from Baja California, Mexico. We found that desert and pine forest toad populations exhibit differences in skin bacterial community structure but show similar Bd infection levels. Using a predictive method, we found that the abundance of bacteria with potential Bd-inhibitory properties differed between uninfected and infected individuals but not between populations. Our data suggest that several bacteria in the skin community may be offering protection from Bd infections in these A. boreas populations. This study provides foundational evidence for future studies seeking to understand the skin-microbial variation among boreal toads' populations and its relation with Bd susceptibility.

Assuntos

RESUMO

Abstract Here, we summarize examples of significant advances in amphibian research supported by the São Paulo Research Foundation (FAPESP), focusing on recent discoveries in the fields of community ecology, habitat change, infection diseases, and multipurpose DNA sequencing. We demonstrated that FAPESP has been fundamental not only by directly funding research projects and scholarships, but also through its science training policy, fostering international collaborations with world-class research institutions, improving and consolidating new lines of research that often depended on a synergetic combination of different knowledge and complex tools. We emphasized that future studies will continue to focus on basic questions, such as description of new species, as well as taxonomic and systematic corrections. Furthermore, we also expect that there will be a strong integration among different disciplines using novel bioinformatics tools and modeling approaches, such as machine learning. These new approaches will be critical to further develop our understanding of foundational questions of amphibian life-history trait variation, disease transmission, community assembly, biogeography, and population forecasts under different global change scenarios such as agricultural expansion, agrochemical use, habitat loss, and climate change.

Resumo No presente estudo apresentamos exemplos de avanços significativos nas pesquisas com anfíbios financiadas pela Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), focando em descobertas recentes nos campos de ecologia de comunidades, modificação do habitat, doenças infecciosas e o sequenciamento de DNA com múltiplos propósitos. Demonstramos que a FAPESP tem sido fundamental não somente pelo financiamento direto de projetos de pesquisa e bolsas de estudo, mas também através de sua política de formação científica, fomentando colaborações internacionais com instituições de pesquisa de excelência mundial, melhorando e consolidando novas linhas de pesquisa que frequentemente dependem da combinação sinérgica entre diferentes linhas de conhecimento e ferramentas complexas. Enfatizamos que futuros estudos continuem com foco em questões básicas, como a descrição de novas espécies, bem como correções taxonômicas e sistemáticas. Além disso, esperamos uma forte integração entre diferentes disciplinas usando novas ferramentas de bioinformática e abordagens de modelagem, como o aprendizado de máquina. Essas novas abordagens serão críticas para desenvolver ainda mais nossa compreensão a respeito de questões fundamentais sobre as características da história de vida dos anfíbios, transmissão de doenças, estrutura de comunidades, biogeografia e previsões populacionais em diferentes cenários de mudanças globais, como a expansão da agricultura, uso de agrotóxicos, perda de habitat e mudanças climáticas.

RESUMO

Batrachochytrium dendrobatidis (Bd) infection is one of the principal causes of amphibian declines worldwide. The presence of Bd has been determined in Gastrotheca riobambae tadpoles that inhabit ponds in Quito's Metropolitan Guangüiltagua Park, Ecuador. This study sought to determine whether these tadpoles are infected and to determine the presence of chytridiomycosis in another frog species, Pristimantis unistrigatus, which also inhabits the park and has different reproductive biology and distinct behavioral habits. We used end-point and real-time PCR techniques to detect and quantify Bd infection. At 1 yr, samples were taken from the skin of P. unistrigatus using swabs and were also taken from the mouthparts of G. riobambae tadpoles. It was found that the two species were infected with a Bd prevalence of 39% (53/135) in G. riobambae tadpoles and 15% (57/382) in P. unistrigatus frogs. The two types of samples (tissue and swabs) from mouthparts showed differences in the zoospores per microliter loads (x̄=1,376.7±3,450.2 vs. x̄=285.0±652.3). Moreover, a correlation (r2=0.621) was discovered between the monthly mean maximum temperature of the pond with disease prevalence in G. riobambae tadpoles. Infection levels in the P. unistrigatus population varied significantly over time, and distance to the pond was a determinant factor for infection intensity.

Assuntos

RESUMO

Amphibian skin bacteria may confer protection against the fungus Batrachochytrium dendrobatidis (Bd), but responses of skin bacteria to different Bd lineages are poorly understood. The global panzootic lineage (Bd-GPL) has caused amphibian declines and extinctions globally. However, other lineages are enzootic (Bd-Asia-2/Brazil). Increased contact rates between Bd-GPL and enzootic lineages via globalization pose unknown consequences for host-microbiome-pathogen dynamics. We conducted a laboratory experiment and used 16S rRNA amplicon-sequencing to assess: (i) whether two lineages (Bd-Asia-2/Brazil and Bd-GPL) and their recombinant, in single and mixed infections, differentially affect amphibian skin bacteria; (ii) and the changes associated with the transition to laboratory conditions. We determined no clear differences in bacterial diversity among Bd treatments, despite differences in infection intensity. However, we observed an additive effect of mixed infections on bacterial alpha diversity and a potentially antagonistic interaction between Bd genotypes. Additionally, observed changes in community composition suggest a higher ability of Bd-GPL to alter skin bacteria. Lastly, we observed a drastic reduction in bacterial diversity and a change in community structure in laboratory conditions. We provide evidence for complex interactions between Bd genotypes and amphibian skin bacteria during coinfections, and expand on the implications of experimental conditions in ecological studies.

Assuntos

RESUMO

Emerging infectious diseases (EIDs) are increasingly recognized as a threat to both biodiversity and human health (Scheele et al., 2019; Wells et al., 2020). But pathogens cannot been seen as unique entities; their intraspecific genetic variability represented in variants, strains, antigenic types or genetic lineages may cause different impacts at the population level (Nelson and Holmes, 2007; Greenspan et al., 2018). The global spread of pathogens has been largely facilitated by globalization of transport, which particularly intensified during the last century (O'Hanlon et al., 2018). As seen with SARS-CoV-2, air travel can rapidly spread a pathogen globally (Wells et al., 2020). Furthermore, after initial introduction subsequent translocations of a pathogen may cause the contact of different variants facilitating the rise of novel genotypes that may have higher pathogenicity or transmissibility (Nelson and Holmes, 2007; Greenspan et al., 2018). Chytridiomycosis is an EID caused by the fungus Batrachochytrium dendrobatidis (Bd), that infects amphibian skin causing population declines to extinction in susceptible species. Now a wildlife pandemic, Bd has been recognized as the single pathogen causing the greatest loss of biodiversity on Earth (Scheele et al., 2019). Recent advances in genetics have made novel tools for pathogen detection and characterization more accessible and reliable (Boyle et al., 2004; Byrne et al., 2019). In this issue of Molecular Ecology Resources, Ghosh et al. (2021) report the development of a new genotyping qPCR assay targeting mitochondrial DNA (mtDNA) of Bd, and based on noninvasive swab samples (Figure 1), discriminate between the two most globally widespread and pathogenic genetic lineages of Bd. Having a better understanding of how the genetic diversity of a pathogen is distributed is crucial to understand their spread patterns and develop timely mitigation strategies.

Assuntos