Chytrid fungus infections in laboratory and introduced Xenopus laevis populations: assessing the risks for U.K. native amphibians

Richard C Tinsley,Peter G Coxhead,Lucy C Stott,Matthew C Tinsley,Maya Z Piccinni,Matthew J Guille

doi:10.1016/j.biocon.2015.01.034

Richard C Tinsley, Peter G Coxhead + Show 4 more

Open Access

https://doi.org/10.1016/j.biocon.2015.01.034

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Abstract

The chytrid fungus Batrachochytrium dendrobatidis (Bd) is notorious amongst current conservation biology challenges, responsible for mass mortality and extinction of amphibian species. World trade in amphibians is implicated in global dissemination. Exports of South African Xenopus laevis have led to establishment of this invasive species on four continents. Bd naturally infects this host in Africa and now occurs in several introduced populations. However, no previous studies have investigated transfer of infection into co-occurring native amphibian faunas. A survey of 27 U.K. institutions maintaining X. laevis for research showed that most laboratories have low-level infection, a risk for native species if animals are released into the wild. RT-PCR assays showed Bd in two introduced U.K. populations of X. laevis, in Wales and Lincolnshire. Laboratory and field studies demonstrated that infection levels increase with stress, especially low temperature. In the U.K., native amphibians may be exposed to intense transmission in spring when they enter ponds to spawn alongside X. laevis that have cold-elevated Bd infections. Exposure to cross-infection has probably been recurrent since the introduction of X. laevis, >20years in Lincolnshire and 50years in Wales. These sites provide an important test for assessing the impact of X. laevis on Bd spread. However, RT-PCR assays on 174 native amphibians (Bufo, Rana, Lissotriton and Triturus spp.), sympatric with the Bd-infected introduced populations, showed no foci of self-sustaining Bd transmission associated with X. laevis. The abundance of these native amphibians suggested no significant negative population-level effect after the decades of co-occurrence.

Highlights

Infection of amphibians by the chytridiomycete fungus Batrachochytrium dendrobatidis (Bd) is currently responsible for a major pandemic whose lethal pathological effects are implicated in widespread extinctions of susceptible host populations
Several amphibian species have been recognised as carriers of infection including the North American bullfrog, Lithobates catesbeianus, and the African clawed frog, Xenopus laevis, both of which have established in novel geographical regions following anthropogenic introduction (Fisher and Garner, 2007)
X. laevis is infected with Bd in several areas of global introduction, this is the first study to investigate the possibility of transfer of infection to sympatric native species

Summary

Introduction

Infection of amphibians by the chytridiomycete fungus Batrachochytrium dendrobatidis (Bd) is currently responsible for a major pandemic whose lethal pathological effects are implicated in widespread extinctions of susceptible host populations. Its epidemiology may create waves of infection accompanied by overwhelming death rates (Cheng et al, 2011; Lips et al, 2006). The origin of this emerging infectious disease (EID) is much debated: interpretations of sudden appearance globally include the ‘novel pathogen hypothesis’ (emphasising anthropogenic dispersal) and the ‘endemic pathogen hypothesis’ (supposing increased susceptibility to pre-existing infection triggered by environmental changes); pathogen hypervirulence may have evolved recently. Several amphibian species have been recognised as carriers of infection including the North American bullfrog, Lithobates catesbeianus, and the African clawed frog, Xenopus laevis, both of which have established in novel geographical regions following anthropogenic introduction (Fisher and Garner, 2007).

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