Rapid global expansion of the fungal disease chytridiomycosis into declining and healthy amphibian populations

• Published in: PLoS pathogens Vol. 5; no. 5; p. e1000458
• Main Authors: James, Timothy Y, Litvintseva, Anastasia P, Vilgalys, Rytas, Morgan, Jess A T, Taylor, John W, Fisher, Matthew C, Berger, Lee, Weldon, Ché, du Preez, Louis, Longcore, Joyce E
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.05.2009; Public Library of Science (PLoS)
• Subjects: Amphibians; Amphibians - microbiology; Animals; Base Sequence; Causes of; Chytridiomycota - genetics; Climate change; Debates; Development and progression; Disease Outbreaks; DNA, Viral; Evolutionary Biology/Evolutionary and Comparative Genetics; Expansion; Genetic aspects; Genetics; Genetics and Genomics/Population Genetics; Genome, Mitochondrial; Genomes; Genotype; Loss of Heterozygosity; Mutation; Mycoses; Physiological aspects; Polymorphism, Genetic; Population; Public Health and Epidemiology/Infectious Diseases; Rana catesbeiana - microbiology; Recombination, Genetic; Reptiles & amphibians; United States
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1000458

The fungal disease chytridiomycosis, caused by Batrachochytrium dendrobatidis, is enigmatic because it occurs globally in both declining and apparently healthy (non-declining) amphibian populations. This distribution has fueled debate concerning whether, in sites where it has recently been found, the pathogen was introduced or is endemic. In this study, we addressed the molecular population genetics of a global collection of fungal strains from both declining and healthy amphibian populations using DNA sequence variation from 17 nuclear loci and a large fragment from the mitochondrial genome. We found a low rate of DNA polymorphism, with only two sequence alleles detected at each locus, but a high diversity of diploid genotypes. Half of the loci displayed an excess of heterozygous genotypes, consistent with a primarily clonal mode of reproduction. Despite the absence of obvious sex, genotypic diversity was high (44 unique genotypes out of 59 strains). We provide evidence that the observed genotypic variation can be generated by loss of heterozygosity through mitotic recombination. One strain isolated from a bullfrog possessed as much allelic diversity as the entire global sample, suggesting the current epidemic can be traced back to the outbreak of a single clonal lineage. These data are consistent with the current chytridiomycosis epidemic resulting from a novel pathogen undergoing a rapid and recent range expansion. The widespread occurrence of the same lineage in both healthy and declining populations suggests that the outcome of the disease is contingent on environmental factors and host resistance.