Thursday, July 28, 2011

Saving Amphibian Diversity by Mitigating Bd

A new article by Woodhams et al. suugests that amphibian diversity can be resuced from the emerging chytrid fungus Batrachochytrium dendrobatidis (Bd). The fungus can exist in amphibians populations as a transient commensal to lethal pathogen. And they suggest a combined strategy of halting pathogen spread and developing survival assurance colonies, as well as prophylactic or remedial disease treatment. Epidemiological models of Bd suggest that mitigation strategies can control disease without eliminating the pathogen. Sustainable conservation of amphibians in nature is dependent on long-term population persistence and co-evolution with potentially lethal pathogens. Therefoe the authors suggest that disease mitigation not focus exclusively on the elimination or containment of the pathogen, or on the captive breeding of amphibian hosts. Instead, successful disease mitigation must be context specific with epidemiologically informed strategies to manage already infected populations by decreasing pathogenicity and host susceptibility. A three step treatment for populations is proposed: first, identify mechanisms of disease suppression; second, parameterize epizootiological models of disease and population dynamics for testing under semi-natural conditions; and third, begin a process of adaptive management in field trials with natural populations. Below is one of the figures from the artlcle.
Some of the rediscovered species in Costa Rica including. A. Craugastor ranoides, B. Atelopus varius, C. Lithobates vibicarius, and D. Pristimantis lemur. Locality data are retained to discourage poaching. E. Climatic refuge in Costa Rica indicated by arrow. The core distribution of Batrachochytrium dendrobatidis (Bd)occurs in humid environments and coincides with the distribution of most declining populations of amphibians. Low abundance relict populations are being rediscovered within Bd enzootic zones, often with subclinical infections. Other species are found outside Bd enzootic zones. Healthy populations, in which a susceptible species maintained high abundance, were found at the edge of the distribution of the robber frog, Craugastor ranoides, in a climatic refuge [138]. Puschendorf et al. ([139]; including details of the bioclimatic model pictured in E) hypothesized that this relict population in the dry forest of Santa Elena Peninsula, Costa Rica, survives because climatic conditions in that habitat make pathogen establishment or persistence on hosts less likely.

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