Mapping the Global Emergence of Batrachochytrium dendrobatidis, the Amphibian Chytrid Fungus

The rapid worldwide emergence of the amphibian pathogen Batrachochytrium dendrobatidis (Bd) is having a profound negative impact on biodiversity. However, global research efforts are fragmented and an overarching synthesis of global infection data is lacking. Here, we provide results from a community tool for the compilation of worldwide Bd presence and report on the analyses of data collated over a four-year period. Using this online database, we analysed: 1) spatial and taxonomic patterns of infection, including amphibian families that appear over-and under-infected; 2) relationships between Bd occurrence and declining amphibian species, including associations among Bd occurrence, species richness, and enigmatic population declines; and 3) patterns of environmental correlates with Bd, including climate metrics for all species combined and three families (Hylidae, Bufonidae, Ranidae) separately, at both a global scale and regional (U. S. A.) scale. These associations provide new insights for downscaled hypothesis testing. The pathogen has been detected in 52 of 82 countries in which sampling was reported, and it has been detected in 516 of 1240 (42%) amphibian species. We show that detected Bd infections are related to amphibian biodiversity and locations experiencing rapid enigmatic declines, supporting the hypothesis that greater complexity of amphibian communities increases the likelihood of emergence of infection and transmission of Bd. Using a global model including all sampled species, the odds of Bd detection decreased with increasing temperature range at a site. Further consideration of temperature range, rather than maximum or minimum temperatures, may provide new insights into Bd-host ecology. Whereas caution is necessary when interpreting such a broad global dataset, the use of our pathogen database is helping to inform studies of the epidemiology of Bd, as well as enabling regional, national, and international prioritization of conservation efforts. We provide recommendations for adaptive management to enhance the database utility and relevance

Mapping the Global Emergence of <em>Batrachochytrium dendrobatidis</em>, the Amphibian Chytrid Fungus

<div><p>The rapid worldwide emergence of the amphibian pathogen <i>Batrachochytrium dendrobatidis</i> (<i>Bd</i>) is having a profound negative impact on biodiversity. However, global research efforts are fragmented and an overarching synthesis of global infection data is lacking. Here, we provide results from a community tool for the compilation of worldwide <i>Bd</i> presence and report on the analyses of data collated over a four-year period. Using this online database, we analysed: 1) spatial and taxonomic patterns of infection, including amphibian families that appear over- and under-infected; 2) relationships between <i>Bd</i> occurrence and declining amphibian species, including associations among <i>Bd</i> occurrence, species richness, and enigmatic population declines; and 3) patterns of environmental correlates with <i>Bd</i>, including climate metrics for all species combined and three families (Hylidae, Bufonidae, Ranidae) separately, at both a global scale and regional (U.S.A.) scale. These associations provide new insights for downscaled hypothesis testing. The pathogen has been detected in 52 of 82 countries in which sampling was reported, and it has been detected in 516 of 1240 (42%) amphibian species. We show that detected <i>Bd</i> infections are related to amphibian biodiversity and locations experiencing rapid enigmatic declines, supporting the hypothesis that greater complexity of amphibian communities increases the likelihood of emergence of infection and transmission of <i>Bd</i>. Using a global model including all sampled species, the odds of <i>Bd</i> detection decreased with increasing temperature range at a site. Further consideration of temperature range, rather than maximum or minimum temperatures, may provide new insights into <i>Bd</i>-host ecology. Whereas caution is necessary when interpreting such a broad global dataset, the use of our pathogen database is helping to inform studies of the epidemiology of <i>Bd</i>, as well as enabling regional, national, and international prioritization of conservation efforts. We provide recommendations for adaptive management to enhance the database utility and relevance.</p> </div

Numbers of species with <i>Batrachochytrium dendrobatidis</i> (<i>Bd</i>) detections by amphibian family, and results of randomisation tests (see Materials and Methods section) to determine whether each sampled amphibian family was over- or under-infected, compared to what we would expect by chance given an overall prevalence of 508/1055 species.

<p>Prev. = Prevalence: <i>Bd</i> detected/Total sampled. * denotes a significant deviation from the expected level of infection in that family. ‘NSD’ = not significant. ‘NA’ denotes that insufficient species had been sampled in that family to detect a significant deviation from a random level of infection. Power-analyses using binomial tests indicated that with six species sampled in a Family, there was sufficient power to detect a deviation in either direction. ‘<i>Bd</i> not detected’ data have limitations, as indicated in Supplemental Information. Notes on taxonomic names used are provided in Supplemental Information. Detections in table updated as of January 2011.</p

Odds of <i>Batrachochytrium dendrobatidis</i> (<i>Bd</i>) detection in amphibians derived from a regression model using data from <i>Bd</i>-maps.net from all species combined (data snapshot July 2010; N = 3,733 locations).

<p>Odds of <i>Batrachochytrium dendrobatidis</i> (<i>Bd</i>) detection in amphibians derived from a regression model using data from <i>Bd</i>-maps.net from all species combined (data snapshot July 2010; N = 3,733 locations).</p

Global locations with enigmatic amphibian declines were positively associated with amphibian species richness (data from GAA [<b>7</b>]), and this relationship increased with the occurrence of the amphibian chytrid fungus, <i>Batrachochytrium dendrobatidis</i>, as modeled with logistic regression.

<p>Dashed lines indicate 95% confidence interval.</p

Numbers of amphibian species and families with <i>Batrachochytrium dendrobatidis</i> detections as of January 2011.

<p>Numbers of amphibian species and families with <i>Batrachochytrium dendrobatidis</i> detections as of January 2011.</p

Global distribution of the amphibian chytrid fungus, <i>Batrachochytrium dendrobatidis</i> (<i>Bd</i>).

<p>Maps downloaded from <a href="http://www.Bd-maps.net" target="_blank">www.Bd-maps.net</a> (15 August 2012); <i>Bd</i>-positive (red) and <i>Bd</i>-negative (white, blue) sites are shown.</p

Extrapolated global maps of the odds of <i>Batrachochytrium dendrobatidis</i> (<i>Bd</i>) detection in amphibians derived from regression models.

<p>The global model using data from all species combined is shown (A), as well as subsets of the world data for species within the amphibian families Bufonidae (B), Hylidae (C), and Ranidae (D). Although these map projections depict the odds of <i>Bd</i> detection at the world scale, it should be noted that amphibians do not occur everywhere in the world, and in particular, the three amphibian families (B,C,D) are not native to all regions world-wide. Significant model parameters differed among models and included landscape-scale site attributes including climate metrics and biotic factors, such as biome or amphibian species richness (see text). Gaps in the mapped models are due to a lack of species richness data, or amphibian absence, for certain regions.</p