The tempo and modes of evolution of reproductive isolation in fungi

Abstract

Reproductive isolation is an essential ingredient of speciation, and much has been learned in recent years about the evolution of reproductive isolation and the genetics of reproductive barriers in animals and plants. Fungi have been neglected on these aspects, despite being tractable model eukaryotes. Here, we used a model fitting approach to look at the importance of different barriers to gene flow to explain the decrease of reproductive compatibility with genetic distance in fungi. We found support for the occurrence of reinforcement in the presyngamy compatibility among basidiomycetes. In contrast, no evidence for reinforcement was detected in ascomycetes, concurring with the idea that host/habitat adaptation in this group can pleiotropically cause reproductive isolation. We found no evidence of a snowballing accumulation of postsyngamic reproductive incompatibilities in either ascomycetes or the complex of anther smut fungi. Together with previous studies, our results suggest that ecologically based barriers to gene flow and karyotypic differences may have an important role in hybrid inviability and sterility in fungi. Interestingly, hybrid sterility appeared to evolve faster than hybrid inviability in fungi.

Within-host competition and diversification of macro-parasites

“…There are also more and more studies revealing the importance and variety of ecological interactions between parasites at the scale of the host body [8,9], including competition [10], facilitation by immuno-suppression [11] and inhibition by the elicitation of non-specific immune response [12]. With the concurrent theoretical and empirical realization that biotic interactions can lead to adaptive diversification in plants [13], fungi [14], algae [15], fishes [16] and various other taxa [17], one expects more adaptive duplication events to be reported as more attention would be given to this overlooked source of parasite diversity.…”

Postzygotic isolation involves strong mitochondrial and sex-specific effects in Tigriopus californicus, a species lacking heteromorphic sex chromosomes

“…Such taxa might therefore be predicted to show slower accumulation of incompatibilities, particularly those causing sterility, with greater symmetry between sexes (Phillips and Edmands, 2012). It is just beginning to be possible to test these predictions with the recent development of models lacking heteromorphic sex chromosomes, such as Helianthus, Mimulus, Solanum, Microbotryum and Saccharomyces (for example, Lowry et al, 2008;Rieseberg and Blackman, 2010;Giraud and Gourbière, 2012). Although firm conclusions would be premature, studies in some of these alternative model systems have shown comparatively modest numbers of incompatibilities (Lowry et al, 2008) and little disparity in the evolution of male vs female sterility (Moyle and Nakazato, 2008).…”

Performance of a Hybrid Fungal Pathogen on Pure-Species and Hybrid Host Plants

“…Previous results on the postmating performance of backcrossed hybrids of MvSl and MvSd on pure-species host indicate that isolation results mainly from ecological incompatibility of hybrids: backcross progenies with a higher proportion of the pathogen genome native to the particular host environment were most fit (Bü ker et al 2013). Even at greater genetic distances, Giraud and Gourbière (2012) found no evidence that negative interactions between loci in divergent lineages contribute to reproductive isolation of fungal species. They again support an ecological basis for hybrid inviability, in which the fitness of hybrid genotypes depends on their ability to cause disease on available hosts .…”

“…These hyphae invade host tissue and colonize meristems of the host, which is sterilized by pollen replacement and abortion of ovaries. There is clearly a genetic basis to variation in host resistance, both within (Alexander and Maltby 1990;Thrall and Jarosz 1994;Alexander and Antonovics 1995;Biere and Antonovics 1996;Carlsson-Granér 1997;Giles et al 2006;Cafuir et al 2007) and between (Antonovics et al 2002;Le Gac et al 2007b;Giraud and Gourbière 2012) closely related host species, as well as to variation between species of Microbotryum in their ability to cause disease (Antonovics et al 2002;Le Gac et al 2007b;Giraud and Gourbière 2012).…”