The chytrid fungus Batrachochytrium dendrobatidis is non‐randomly distributed across amphibian breeding habitats

Abstract

The chytrid fungus Batrachochytrium dendrobatidis has been implicated as the causative agent of mass mortalities, population declines, and the extinctions of stream‐breeding amphibian species worldwide. While the factors that limit the distribution and abundance of B. dendrobatidis across large geographical regions are fairly well understood, little is known about the distribution of the fungus within localized areas such as individual catchments. The accurate identification of amphibian populations likely to be exposed to the fungus is urgently required for effective disease management. We conducted disease surveys of frogs representing five ecological guilds in south‐east Queensland, Australia, and hypothesized that if B. dendrobatidis were responsible for the disappearance of stream‐breeding amphibian populations, infection prevalence and intensity would be greatest in frogs breeding in permanent, flowing water. Overall, 30.3% of the 519 frogs we sampled were infected with B. dendrobatidis. However, infections were not evenly distributed across the ecological guilds, being almost completely restricted to frogs breeding at permanent waterbodies. Of these, stream breeders were significantly more likely to be infected than were pond breeders, though the intensity of frogs’ infections did not differ significantly between the two guilds. Batrachochytrium dendrobatidis was detected on only one of the 117 frogs that were found at ephemeral ponds, ephemeral streams, or terrestrial sites. These findings provide strong support for the hypothesis that B. dendrobatidis was responsible for many of the unexplained disappearances of stream‐breeding amphibian populations in recent decades, and will enable wildlife managers to more accurately focus conservation efforts on those species at highest risk of disease‐related decline.

A molecular perspective: biology of the emerging pathogen Batrachochytrium dendrobatidis

“…For example, studies on disease progression in heavily infected areas such as eastern Australia show that host traits, such as breeding habitat and production of antimicrobial peptides, are better predictors of susceptibility than host taxonomy (Woodhams et al 2006, Kriger & Hero 2007b. However, the possibility of hostpathogen coevolution merits further investigation because predicting host susceptibility is essential for preventing future species extinctions.…”

Partitioning the net effect of host diversity on an emerging amphibian pathogen

“…We hypothesized that natural species-rich communities are more likely to include competent hosts for Bd than depauperate ones, increasing pathogen transmission. For instance, natural species-rich communities include a higher proportion of stream-dwelling specialists [54,55] that often carry higher Bd infection intensities in the wild [25,29]. Most host species in these diverse natural communities may have had a higher likelihood of suffering Bd spillover from the highly infected stream dwellers, such as species of Atelopus in Central America [25] and Taudactylus in Australia [56].…”

“…We assigned a host aquatic index (AI) to each species (adapted from [28]), which quantifies the amount of time spent in aquatic environments summed across different amphibian life stages. Because Bd is a water-borne fungal pathogen, AI also serves as a relative measure of species-specific exposure and transmission probability in natural communities [29,30]. Our seven focal host species ranged from exclusively terrestrial species (i.e.…”

Prevalence of Batrachochytrium Dendrobatidis in Agalychnis Moreletii (Hylidae) of El Salvador and Association With Larval Jaw Sheath Depigmentation

“…It is unlikely that our initial sampling activities introduced Bd to El Imposible; in addition to cleaning boots and other gear between each site, El Imposible was the first site that we sampled for larvae and was therefore sampled using new nets. In other anurans, changes in Bd prevalence have been associated with seasonal temperature variation (e.g., Retallick et al, 2004;McDonald et al, 2005;Kriger and Hero, 2007). However, temperature shows little seasonal variation in El Salvador (Guzmá n Ló pez, 1995).…”