Amphibian chytrid infection is influenced by rainfall seasonality and water availability

Abstract

Amphibians suffer from a number of factors that make them the most threatened group of vertebrates. One threat is the fungal disease chytridiomycosis caused by the emerging pathogen Batrachochytrium dendrobatidis (Bd), which has rapidly spread and caused the loss of massive amphibian biodiversity worldwide. Recently, Bd was associated with a few amphibian population declines and extinctions in some areas of the Brazilian Atlantic Forest. However, the mechanisms underlying such declines are not fully understood. Therefore, it is essential to improve our knowledge of abiotic factors that can possibly influence Bd prevalence and chytridiomycosis disease severity. Herein we tested the hypothesis that water availability (such as in perennial streams, where Bd is frequently present in larvae) and rainfall would increase the prevalence of Bd. To test this, we sampled frogs from 6 transects with different numbers of perennial waterbodies, and we report that the more water available in the area, the higher the probability of Bd infection on anurans. Seasonality also influenced both the Bd prevalence in the area and the intensity of infection in infected frogs. However, Bd prevalence was higher during the rainy months whereas the infection burden was lower. We suggest that Bd is likely spread during the summer, when most anuran species gather near the water for spawning and when rainfall overfills ephemeral wetlands. On the other hand, during the drier months, a higher infection burden may be explained by increased disease susceptibility.

Hybrids of amphibian chytrid show high virulence in native hosts

“…However, both of our terrestrial study species acquired heavy Bd infections and experienced mortality from chytridiomycosis under laboratory conditions mimicking the microhabitat of direct-developing frogs in nature, consistent with laboratory data for other Brazilian direct-developing species 63 . In the wild, Brazilian direct-developers had high Bd infection loads 71 , 72 , but low infection prevalence 63 , the latter of which could be underestimated if frogs die quickly from infections or if sick frogs remain stationary in hidden refugia 63 , 73 . Even if low prevalence of Bd is currently facilitating population persistence of direct-developing host species in Brazil, this host-pathogen balance is precarious in an era of global change 61 .…”

Known and estimated distribution in Mexico of Batrachochytrium dendrobatidis, a pathogenic fungus of amphibians

“…Summer is also the amphibians’ reproductive season and when many of them are most active (Aichinger, ; Lips et al., ; Saenz, Fitzgerald, Baum, Conner & Adams, ). We think that the combination of suitable environmental factors and a greater number of possible hosts facilitates the dispersal of Bd in the environment (Briggs, Knapp & Vredenburg, ; Ruggeri, Potsch de Carvalho‐e‐Silva, James & Toledo, ).…”

Spatiotemporal heterogeneity decouples infection parameters of amphibian chytridiomycosis

“…In order to measure environmental variation at a scale relevant to the host, temperature and precipitation were averaged across two specific time points: (a) period prior to host breeding and (b) during host breeding. Based on a priori hypotheses regarding the effects of environmental factors on Bd disease dynamics, we hypothesize that: (a) during the active period, cooler temperatures and greater precipitation will be associated with increased prevalence and infection intensity in late summer (Bosch, Carrascal, Duran, Walker, & Fisher, ; Piotrowski, Annis, & Longcore, ; Puschendorf et al, ), due to increased opportunities for successful Bd transmission (Lampo, Rodriguez‐Contreras, Marca, & Daszak, ); (b) during the breeding period, as water basins and rivers serve as likely vectors for the waterborne zoospores (Kriger & Hero, ), an increase in basin size will lower intensity due to diluted zoospore concentrations (Briggs, Knapp, & Vredenburg, ), while a reduction in river density will limit transmission nodes, thus lowering prevalence and infection intensity (Ruggeri, Carvalho‐e‐Silva, James, & Toledo, ; Sapsford, Alford, & Schwarzkopf, ); and (c) increased road density will intensify landscape fragmentation leading to isolated habitat patches and dense host populations, which will allow for an increase in overall prevalence and intensity (Balkenhol & Waits, ; Greer & Collins, ).…”