Disease-associated change in an amphibian life-history trait
Emerging pathogens can drive evolutionary shifts in host life-history traits, yet this process remains poorly documented in vertebrate hosts. Amphibian chytridiomycosis, caused by infection with the fungal pathogen Batrachochytrium dendrobatidis (Bd), is the worst recorded wildlife disease and has caused the extinction of over 100 species across multiple continents. A similar number of additional species have experienced mass declines and Bd remains a major source of mortality in many populations of declined species now persisting with the pathogen. Life-history theory predicts that increased extrinsic mortality in Bd-infected populations may alter amphibian life-history traits, but this has not been examined. Here, we investigate whether population Bd status is associated with age and size at maturity by comparing long-exposed Bd-infected populations, Bd-free populations, and museum specimens collected prior to Bd emergence for the endangered Australian frog Litoria verreauxii alpina. We show that Bd-infected populations have a higher proportion of males that mature at 1 year of age, and females that mature at 2 years of age, compared to Bd-free populations. Earlier maturation was associated with reduced size at maturity in males. Consistent with life-history theory, our findings may represent an adaptive evolutionary shift towards earlier maturation in response to high Bd-induced mortality. To our knowledge, this study provides the first evidence for a post-metamorphic Bd-associated shift in an amphibian life-history trait. Given high mortality in other Bd-challenged species, we suggest that chytridiomycosis may be a substantial new selection pressure shaping life-history traits in impacted amphibian species across multiple continents.
KeywordsBatrachochytrium dendrobatidis Chytrid fungus Maturation rates Pathogen Wildlife disease
Funding was provided by a Taronga Zoo Field Conservation Grant and the New South Wales Office of Environment and Heritage. B.C. Scheele and L. Berger were supported by Australian Research Council Grants LP110200240 and FT100100375, which included additional funding from industry partners Taronga Zoo and New South Wales Office of Environment and Heritage during the writing of this manuscript. C. Scheele and S. Kearney provided field assistance, K. Smith and L. Brannelly helped facilitate museum sampling, and C. Foster provided statistical advice and helped with figures. All applicable institutional and/or national guidelines for the care and use of animals were followed, with research conducted under scientific permits SL100436 and SL10006052 issued by the New South Wales Office of Environment and Heritage and animal ethics approval from the Australian National University (A2011/19) and the University of Canberra (CEAE 98/7).
Author contribution statement
BCS, LFS, DAH, JCP, DAD, SCB, PGB, and LB conceived and designed the research. BCS and DAH performed field and laboratory work. BCS analysed data. BCS wrote the manuscript and all authors contributed editorial advice.
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