Amphibian‐killing chytrid in Brazil comprises both locally endemic and globally expanding populations

Abstract

Chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), is the emerging infectious disease implicated in recent population declines and extinctions of amphibian species worldwide. Bd strains from regions of disease-associated amphibian decline to date have all belonged to a single, hypervirulent clonal genotype (Bd-GPL). However, earlier studies in the Atlantic Forest of southeastern Brazil detected a novel, putatively enzootic lineage (Bd-Brazil), and indicated hybridization between Bd-GPL and Bd-Brazil. Here, we characterize the spatial distribution and population history of these sympatric lineages in the Brazilian Atlantic Forest. To investigate the genetic structure of Bd in this region, we collected and genotyped Bd strains along a 2400-km transect of the Atlantic Forest. Bd-Brazil genotypes were restricted to a narrow geographic range in the southern Atlantic Forest, while Bd-GPL strains were widespread and largely geographically unstructured. Bd population genetics in this region support the hypothesis that the recently discovered Brazilian lineage is enzootic in the Atlantic Forest of Brazil and that Bd-GPL is a more recently expanded invasive. We collected additional hybrid isolates that demonstrate the recurrence of hybridization between panzootic and enzootic lineages, thereby confirming the existence of a hybrid zone in the Serra da Graciosa mountain range of Paraná State. Our field observations suggest that Bd-GPL may be more infective towards native Brazilian amphibians, and potentially more effective at dispersing across a fragmented landscape. We also provide further evidence of pathogen translocations mediated by the Brazilian ranaculture industry with implications for regulations and policies on global amphibian trade.

Probiotic consortia are not uniformly effective against different amphibian chytrid pathogen isolates

“…Scenario 3: We also tested the ability of both multigenus and single‐genus consortia to inhibit the growth of two different B. dendrobatidis isolates in series, as individuals in a single location may be exposed to multiple variants of a pathogen (Goka et al., ; Jenkinson et al., ; Rodriguez et al., ; Schloegel et al., ), or strong spatial structure of the pathogen and high host dispersal may expose individuals to multiple pathogen variants consecutively. Applying the same multigenus consortium to two different randomly chosen B. dendrobatidis isolates in series achieved stronger inhibition than single‐genus consortia in 49.4% of cases (null expectation 25%, p RAND <0.001).…”

Diverse genotypes of the amphibian‐killing fungus produce distinct phenotypes through plastic responses to temperature

“…Larger Bd zoospore size, larger zoosporangium size, slower growth rate and higher carrying capacity are correlated with higher Bd infection loads and higher amphibian mortality (Becker et al., ; Fisher et al., ; Lambertini et al., ; Piovia‐Scott et al., ; Voyles, ; Voyles et al., ). Bd‐Brazil produced the smallest zoospores and zoosporangia across temperatures, which may explain the lower virulence and infectiveness of Bd‐Brazil compared to Bd‐GPL and the GPL‐Brazil hybrid (Greenspan et al., ; Jenkinson et al., ; Rodriguez, Becker, Pupin, Haddad, & Zamudio, ). We quantified these phenotypic traits in vitro as the same stages of the life cycle occur within epidermal cells of amphibian skin as in culture (Berger et al., ).…”

“…We selected three temperatures (12, 18 and 24°C) within the temperature range for Bd growth (Piotrowski et al., ; Stevenson et al., ; Voyles et al., ). We selected isolates that were genotyped in previous studies (Jenkinson et al., ; Schloegel et al., ) and represented genetic diversity within and among Bd lineages, including the Bd‐Brazil lineage, a Bd‐Brazil‐GPL hybrid and several Bd‐GPL genotypes.…”

“…In our analyses, detecting phylogenetic dependence of traits would indicate phylogenetic signal, but not detecting phylogenetic dependence could relate to a lack of power. To construct the phylogenetic tree of the Bd lineages, we used the neighbor‐joining algorithm in PAUP*4.0 based on concatenated multilocus genotypes for 36 loci from multiple chromosomal regions (Jenkinson et al., ; Schloegel et al., ), midpoint rooted the tree using the function midpoint.root in the package “phytools” (Revell, ) and transformed the topology to an ultrametric tree using the function chronos in the package “ape” (Paradis, Claude, & Strimmer, ). For phenotypic trait values, we used the mean parameter estimate from the morphological size and growth models (Supporting Information Table S1).…”

Resistance, tolerance and environmental transmission dynamics determine host extinction risk in a load‐dependent amphibian disease

“…; Jenkinson et al . ). Load dynamics are important in Bd systems because disease‐induced mortality of amphibians is highly load‐dependent, with survival probability sometimes decreasing rapidly at high Bd loads (Stockwell et al .…”