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Hybridization Facilitates Adaptive Evolution in Two Major Fungal Pathogens

1
Department of Biology, McMaster University, 1280 Main St. W, Hamilton, ON L8S 4K1, Canada
2
Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720, USA
3
Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA
*
Author to whom correspondence should be addressed.
These authors contributed equally to the work.
Genes 2020, 11(1), 101; https://doi.org/10.3390/genes11010101
Received: 20 December 2019 / Revised: 2 January 2020 / Accepted: 14 January 2020 / Published: 16 January 2020
(This article belongs to the Special Issue Genome Plasticity of Human and Plant Pathogenic Fungi)
Hybridization is increasingly recognized as an important force impacting adaptation and evolution in many lineages of fungi. During hybridization, divergent genomes and alleles are brought together into the same cell, potentiating adaptation by increasing genomic plasticity. Here, we review hybridization in fungi by focusing on two fungal pathogens of animals. Hybridization is common between the basidiomycete yeast species Cryptococcus neoformans × Cryptococcus deneoformans, and hybrid genotypes are frequently found in both environmental and clinical settings. The two species show 10–15% nucleotide divergence at the genome level, and their hybrids are highly heterozygous. Though largely sterile and unable to mate, these hybrids can propagate asexually and generate diverse genotypes by nondisjunction, aberrant meiosis, mitotic recombination, and gene conversion. Under stress conditions, the rate of such genetic changes can increase, leading to rapid adaptation. Conversely, in hybrids formed between lineages of the chytridiomycete frog pathogen Batrachochytrium dendrobatidis (Bd), the parental genotypes are considerably less diverged (0.2% divergent). Bd hybrids are formed from crosses between lineages that rarely undergo sex. A common theme in both species is that hybrids show genome plasticity via aneuploidy or loss of heterozygosity and leverage these mechanisms as a rapid way to generate genotypic/phenotypic diversity. Some hybrids show greater fitness and survival in both virulence and virulence-associated phenotypes than parental lineages under certain conditions. These studies showcase how experimentation in model species such as Cryptococcus can be a powerful tool in elucidating the genotypic and phenotypic consequences of hybridization. View Full-Text
Keywords: Cryptococcus; AD hybrids; frog chytrid; reproductive incompatibilities; aneuploidy Cryptococcus; AD hybrids; frog chytrid; reproductive incompatibilities; aneuploidy
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Samarasinghe, H.; You, M.; Jenkinson, T.S.; Xu, J.; James, T.Y. Hybridization Facilitates Adaptive Evolution in Two Major Fungal Pathogens. Genes 2020, 11, 101.

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