Complex history of chytrid

[Frog News]

AJC's Frogroom (UK) May 7th, 2013 08:59 AM: Complex history of chytrid


Scientists have just published a complicated scientific paper on the devastating amphibian pathogen Batrachochytrium dendrobatidis (Bd - chytrid). The full version is below, but here's the summary:

They sequenced the genome from 29 isolates of Bd from around the world and found a lot more genetic variation than previously reported. So what? This means that the worldwide chytrid "pandemic" is more complicated than previously thought, and one size does not fit all outbreaks.

The major disease-linked amphibian population declines predate the late 20th century emergence of this pathogen in amphibians. Is Bd was simply an unrecognized member of amphibian communities that suddenly turned lethal and is it a new pathogen? This new data Bd shows that Bd has been in some amphibian populations for a very long time. In others it is a recent introduction. Proteases are confirmed as important in Bd infection of amphibian skin and in causing the disease.

The history of the chytrid pandemic is complex and a long way away from the idea that a "new" disease suddenly wiped out many of the world's amphibians.



Complex history of the amphibian-killing chytrid fungus revealed with genome resequencing data. PNAS USA 06 May 2013, doi: 10.1073/pnas.1300130110
Understanding the evolutionary history of microbial pathogens is critical for mitigating the impacts of emerging infectious diseases on economically and ecologically important host species. We used a genome resequencing approach to resolve the evolutionary history of an important microbial pathogen, the chytrid Batrachochytrium dendrobatidis (Bd), which has been implicated in amphibian declines worldwide. We sequenced the genomes of 29 isolates of Bd from around the world, with an emphasis on North, Central, and South America because of the devastating effect that Bd has had on amphibian populations in the New World. We found a substantial amount of evolutionary complexity in Bd with deep phylogenetic diversity that predates observed global amphibian declines. By investigating the entire genome, we found that even the most recently evolved Bd clade (termed the global panzootic lineage) contained more genetic variation than previously reported. We also found dramatic differences among isolates and among genomic regions in chromosomal copy number and patterns of heterozygosity, suggesting complex and heterogeneous genome dynamics. Finally, we report evidence for selection acting on the Bd genome, supporting the hypothesis that protease genes are important in evolutionary transitions in this group. Bd is considered an emerging pathogen because of its recent effects on amphibians, but our data indicate that it has a complex evolutionary history that predates recent disease outbreaks. Therefore, it is important to consider the contemporary effects of Bd in a broader evolutionary context and identify specific mechanisms that may have led to shifts in virulence in this system.













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