Climate structuring ofBatrachochytrium dendrobatidisinfection in the threatened amphibians of the northern Western Ghats, India

Abstract

Batrachochytrium dendrobatidis (Bd) is a pathogen killing amphibians worldwide. Its impact across much of Asia is poorly characterized. This study systematically surveyed amphibians for Bd across rocky plateaus in the northern section of the Western Ghats biodiversity hotspot, India, including the first surveys of the plateaus in the coastal region. These ecosystems offer an epidemiological model system since they are characterized by differing levels of connectivity, edaphic and climatic conditions, and anthropogenic stressors. One hundred and eighteen individuals of 21 species of Anura and Apoda on 13 plateaus ranging from 67 to 1179 m above sea level and 15.89 to 17.92° North latitude were sampled. Using qPCR protocols, 79% of species and 27% of individuals tested were positive for Bd. This is the first record of Bd in caecilians in India, the Critically Endangered Xanthophryne tigerina and Endangered Fejervarya cf. sahyadris. Mean site prevalence was 28.15%. Prevalence below the escarpment was 31.2% and 25.4% above. The intensity of infection (GE) showed the reverse pattern. Infection may be related to elevational temperature changes, thermal exclusion, inter-site connectivity and anthropogenic disturbance. Coastal plateaus may be thermal refuges from Bd. Infected amphibians represented a wide range of ecological traits posing interesting questions about transmission routes.

Infection with Batrachochytrium dendrobatidis is common in tropical lowland habitats: Implications for amphibian conservation

“…Low sample sizes were caused by low detectability during the survey period for some of the common species (e.g., Rhinella horribilis, Smilisca sordida, Lithobates vaillanti, Leptodactylus savagei ) or due to the low year‐round detectability for the more cryptic and rare species (e.g., fossorial and canopy dwellers like Oedipina gracilis, Bolitoglossa colonnea, Cruziohyla calcarifer ). To increase species detectability and/or sample size, future studies in lowlands and neglected sites should conduct surveys restricting or focusing the sampling on threatened species (Thorpe et al, ; Whitfield et al, ), to describe host–pathogen population dynamics, or preferably survey multiple species across seasons to obtain more accurate estimates of prevalence and infection intensity for all species within the amphibian community (Brannelly et al, ; Kinney et al, ; Vredenburg et al, ).…”

Chytridiomycosis in Asian Amphibians, a Global Resource for Batrachochytrium dendrobatidis (Bd) Research

“…Latitude, elevation, and seasonality have varied influences prevalence and load of Bd in hotspots of infection 17 – 19 . In coldspots, seasonal fluctuation in Bd prevalence has been recorded 29 , 30 , 38 . Detection of these patterns at a population level and inferring infection by the pathogen requires appropriate designs of amphibian monitoring programs.…”

“…In Giant Japanese Salamander, Andrias japonicas a museum specimen from 1902 had Bd on its skin 26 . After this, a series of efforts were made to document prevalence of Bd infection from different parts of Asia 27 – 38 . Lethal outbreak of the infection has so far not been recorded from Asia and therefore, it is referred to as a ‘coldspot’ of Bd infection.…”

Ancestral chytrid pathogen remains hypervirulent following its long coevolution with amphibian hosts

“…Yet, epizootics and population extirpations associated with the disease elsewhere in the world have not been witnessed on the continent, nor have clinical signs of amphibian chytridiomycosis been reported. Many Asian amphibians harbour low infection loads of the amphibian chytrid pathogens Batrachochytrium dendrobatidis (hereafter denoted Bd) and Batrachochytrium salamandrivorans [10][11][12][13]. Their effects on hosts, if any, are sublethal; they may affect host life histories [14] and, potentially, long-term population stability [15].…”