Abstract
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.
Highlights
Hybridization refers to the interbreeding of individuals from genetically distinct populations or species
F1 hybrids often display aneuploidy, diploidy, or higher ploidy, and because of the extra chromosome copies they can continue to diversify and adapt through mechanisms such as mitotic recombination and the gain/loss of individual chromosomes. We explore these issues with a fungal view of hybridization described using two major fungal pathogens, the human-pathogenic Cryptococcus species and the amphibian chytrid fungus
Basidiospores produced by three self-fertile AD hybrids containing both mating types germinated at a very low rate of ~5% in laboratory conditions: these three AD hybrids did not produce any sexual spores when co-incubated with haploid MATa and MATα strains of C. neoformans and C. deneoformans [52]
Summary
Hybridization refers to the interbreeding of individuals from genetically distinct populations or species. Fungi are unique from the better-studied plants and animals in that they often produce copious (literally millions or billions) amounts of recombinants from a single mating event, which could lead to the generation of immense diversity. They are unique because their dispersal is not considered limited, such that traditional hybrid zones of a limited geographic extent seem unlikely. Many fungi display a mixed mode of reproduction, with extensive generations of asexual reproduction interspersed with rare sexual reproduction [11] Such versatility in reproduction could allow hybrids to propagate asexually for extended periods of time without suffering from a potential segregation load [12]. Insights into hybridization in these species require different approaches, but much has been revealed and facilitated by genomics
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
