Is Chytridiomycosis Driving Darwin’s Frogs to Extinction?

Claudio Soto-Azat,Andrés Valenzuela-Sánchez,Barry T Clarke,Juan Carlos Ortiz,Carlos Barrientos,Klaus Busse,Andrew A Cunningham,Michael Sears

doi:10.1371/journal.pone.0079862

Abstract

Darwin’s frogs (Rhinoderma darwinii and R. rufum) are two species of mouth brooding frogs from Chile and Argentina that have experienced marked population declines. Rhinoderma rufum has not been found in the wild since 1980. We investigated historical and current evidence of Batrachochytrium dendrobatidis (Bd) infection in Rhinoderma spp. to determine whether chytridiomycosis is implicated in the population declines of these species. Archived and live specimens of Rhinoderma spp., sympatric amphibians and amphibians at sites where Rhinoderma sp. had recently gone extinct were examined for Bd infection using quantitative real-time PCR. Six (0.9%) of 662 archived anurans tested positive for Bd (4/289 R. darwinii; 1/266 R. rufum and 1/107 other anurans), all of which had been collected between 1970 and 1978. An overall Bd-infection prevalence of 12.5% was obtained from 797 swabs taken from 369 extant individuals of R. darwinii and 428 individuals representing 18 other species of anurans found at sites with current and recent presence of the two Rhinoderma species. In extant R. darwinii, Bd-infection prevalence (1.9%) was significantly lower than that found in other anurans (7.3%). The prevalence of infection (30%) in other amphibian species was significantly higher in sites where either Rhinoderma spp. had become extinct or was experiencing severe population declines than in sites where there had been no apparent decline (3.0%; x 2 = 106.407, P<0.001). This is the first report of widespread Bd presence in Chile and our results are consistent with Rhinoderma spp. declines being due to Bd infection, although additional field and laboratory investigations are required to investigate this further.

Highlights

There are two species of Darwin’s frogs, both of which inhabit the temperate forests of South America: the northern Darwin’s frog (Rhinoderma rufum), which is endemic to central Chile, and the southern Darwin’s frog (R. darwinii), which is found in south and southern Chile and in adjacent areas of Argentina [1,2]
It has been hypothesised that amphibian chytridiomycosis, an infectious disease caused by the nonhyphal zoosporic chytrid fungus, Batrachochytrium dendrobatidis (Bd), might be implicated in the disappearances of Darwin’s frogs [1,2,8]
Batrachochytrium dendrobatidis in archived amphibians Six (0.9%) of 662 archived anurans were positive for Bd

Summary

Introduction

There are two species of Darwin’s frogs, both of which inhabit the temperate forests of South America: the northern Darwin’s frog (Rhinoderma rufum), which is endemic to central Chile, and the southern Darwin’s frog (R. darwinii), which is found in south and southern Chile and in adjacent areas of Argentina [1,2]. The behaviour that sets these frogs apart from all other amphibians is that the males care for their young by incubating them in their vocal sacs for at least part of their development, a process known as neomelia [3,4] In recent decades, both species have undergone marked population declines and R. rufum has not been recorded since 1980 [5]. Does not fully explain the enigmatic disappearances of R. rufum from its entire historical range or of the declines of R. darwinii from undisturbed ecosystems, including National Parks [8] In this context, it has been hypothesised that amphibian chytridiomycosis, an infectious disease caused by the nonhyphal zoosporic chytrid fungus, Batrachochytrium dendrobatidis (Bd), might be implicated in the disappearances of Darwin’s frogs [1,2,8]

Methods

Results

Conclusion