Chromosomal copy number variation, selection and uneven rates of recombination reveal cryptic genome diversity linked to pathogenicity

PLoS Genet. 2013;9(8):e1003703. doi: 10.1371/journal.pgen.1003703. Epub 2013 Aug 15.


Pathogenic fungi constitute a growing threat to both plant and animal species on a global scale. Despite a clonal mode of reproduction dominating the population genetic structure of many fungi, putatively asexual species are known to adapt rapidly when confronted by efforts to control their growth and transmission. However, the mechanisms by which adaptive diversity is generated across a clonal background are often poorly understood. We sequenced a global panel of the emergent amphibian pathogen, Batrachochytrium dendrobatidis (Bd), to high depth and characterized rapidly changing features of its genome that we believe hold the key to the worldwide success of this organism. Our analyses show three processes that contribute to the generation of de novo diversity. Firstly, we show that the majority of wild isolates manifest chromosomal copy number variation that changes over short timescales. Secondly, we show that cryptic recombination occurs within all lineages of Bd, leading to large regions of the genome being in linkage equilibrium, and is preferentially associated with classes of genes of known importance for virulence in other pathosystems. Finally, we show that these classes of genes are under directional selection, and that this has predominantly targeted the Global Panzootic Lineage (BdGPL). Our analyses show that Bd manifests an unusually dynamic genome that may have been shaped by its association with the amphibian host. The rates of variation that we document likely explain the high levels of phenotypic variability that have been reported for Bd, and suggests that the dynamic genome of this pathogen has contributed to its success across multiple biomes and host-species.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amphibians / genetics
  • Amphibians / microbiology
  • Animals
  • Base Sequence
  • Chromosomes
  • Chytridiomycota / genetics*
  • Chytridiomycota / pathogenicity*
  • DNA Copy Number Variations
  • Genetic Variation*
  • Genotype
  • Host-Pathogen Interactions / genetics*
  • Recombination, Genetic / genetics*

Grant support

This project was funded by the UK Natural Environmental Research Council (NERC) grant NE/E006701/1, the European Research Council (ERC) grant 260801-BIG_IDEA, the Swiss National Science Foundation grant 31-125099 and the Biodiversa project RACE: Risk Assessment of Chytridiomycosis to European Amphibian Biodiversity ( The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.