Population structure of two beetle-associated yeasts: comparison of a New World asexual and an endemic Nearctic sexual species in the Metschnikowia clade

Abstract

The genetic structure of two related yeast species, one sexual and one asexual, was compared using polymorphic DNA markers. Although both yeasts propagate by asexual budding of haploid cells, Metschnikowia borealis reproduces sexually when compatible strains come in contact. To what extent this has occurred in nature was not known. As Candida ipomoeae is a closely related, asexual species, the two yeasts provide an excellent model system to assess the role of sexual reproduction in a biogeographic context. Natural isolates of the two species were characterized using several polymorphic DNA markers. As predicted for an organism whose reproduction is strictly clonal, C. ipomoeae exhibited low haplotype diversity, high linkage disequilibrium, and high population differentiation. In contrast, M. borealis had unique haplotypes in most isolates, lower population differentiation, and little linkage disequilibrium, demonstrating that sexual recombination is prevalent. Geographic gradients were identified in both species, indicating that historical and climatic factors both play a role in shaping the populations. The spatial structure is also thought to be influenced by the ecology of the small floricolous beetles (family Nitidulidae) that vector the yeasts. For example, Hawaiian strains of C. ipomoeae show evidence of having undergone a genetic bottleneck, most likely when the vector was introduced to the islands. The two haplotypes found in Hawaii were nearly identical and were also found in North and Central America. M. borealis had a more continuous distribution where the genetic markers follow latitudinal and longitudinal gradients.

The expanding large-spored Metschnikowia clade: Metschnikowia matae sp. nov., a yeast species with two varieties from the Brazilian Atlantic Forest

“…nov. var. The sister pair consisting of M. borealis and strain 13-106.1 recovered in Florida occupies a short latitudinal gradient on the east coast of North America, as the former species is known to occur as far south as Tennessee (Wardlaw et al 2009). The strains represent three phylotypes of the variety (Fig.…”

“…The first report was for Metschnikowia hawaiiensis (Lachance et al 1990), which is endemic to the Island of Hawaii. More specifically the subclade members are endemic either to the northeastern part of North America (M. borealis, Wardlaw et al 2009), to Cuba (M. cubensis, Fidalgo-Jiménez et al 2008, to Florida (strain 13-106.1), or to Central America (M. santaceciliae, Lachance et al 2003). The clade is particularly interesting by its biogeography, as most species are endemic.…”

“…The clade is particularly interesting by its biogeography, as most species are endemic. Metschnikowia (Candida) ipomoeae is unusual in that it ranges across the hemispheres, from Brazil to Tennessee, and occurs mostly in the asexual state (Wardlaw et al 2009). Another contains six species known only from localities in the Hawaiian archipelago (Lachance et al 2005).…”

The use of parsimony network analysis for the formal delineation of phylogenetic species of yeasts: Candida apicola, Candida azyma, and Candida parazyma sp. nov., cosmopolitan yeasts associated with floricolous insects

“…Greig (2007) pointed out that yeasts are probably not free-living because of their complex interactions with vector insects and suggested that Saccharomyces species probably do have a biogeography, a prediction that seems to have received strong support recently from phylogenomic studies (Liti et al 2009). So far, yeasts found in association with floricolous insects have followed strong biogeographic patterns, be it at the supraspecific (Lachance et al 2001(Lachance et al , 2005 or the infraspecific (Lachance et al 2008;Wardlaw et al 2009) levels. The analysis depicted in Fig.…”

Phylogenetic analysis of the angiosperm-floricolous insect–yeast association: Have yeast and angiosperm lineages co-diversified?

“…Despite the fact that Metschnikowia includes some of the beststudied yeasts in terms of biogeography and ecology (Lachance et al, 2008;Wardlaw et al, 2009) a proper phylogeny of the genus has not been proposed to date. Previous molecular phylogenetic analyses have been based on relatively short rDNA sequences (generally of few hundred nucleotides) (Mendoça-Hagler et al, 1993;Yamada et al, 1994) or the sampling has been limited to a group of species (i.e.…”