Patterns of within population dispersal and mating of the fungus Microbotryum violaceum parasitising the plant Silene latifolia

Abstract

This study explores the patterns of dispersal and mating of the anther smut Microbotryum violaceum, a model species in genetics and evolutionary biology. A French metapopulation of the fungus collected from its caryophyllaceous host Silene latifolia was analysed using microsatellites. The genetic diversity was low, populations were strongly differentiated, and there was no pattern of isolation by distance among populations. There was a strong deficit in heterozygotes, confirming the high self-fertilisation rates suggested by previous studies. Within populations there was a strong pattern of isolation by distance, with identical genotypes being highly clustered. This indicates that fungal spores are dispersed mostly between adjacent plants, and such local dispersal is important for understanding the dynamics and evolution of this disease. Local clusters of identical heterozygous genotypes did not contain significantly fewer individuals than did clusters of homozygous genotypes. As selfing between products of independent meiotic events (intertetrad selfing) rapidly reduces heterozygosity, this suggests that intratetrad matings are frequent, which helps to explain the puzzling maintenance of a sex-ratio distortion in M. violaceum. Heredity (2004) 93, 559-565.

DNA polymorphism in recombining and non-recombing mating-type-specific loci of the smut fungus Microbotryum

“…In accordance with published microsatellite-based results (Bucheli et al, 2001;Giraud, 2004; Granberg et al, 2008), we observed a very low proportion of heterozygotes in our sequence data in M. violaceum: only two out of the nineteen individuals in our study had any heterozygous sites in any of the non-mating-type-linked loci studied. A high degree of selfing inflates homozygosity, which leads to a low effective recombination rate in the recombining regions and reduces the difference between the recombining and non-recombining regions.…”

“…This leads to high degree of selfing, which is expected to reduce diversity throughout the genome. Indeed, the analysis of microsatellite diversity revealed high homozygosity (Bucheli et al, 2001;Giraud, 2004;Granberg et al, 2008). However, DNA diversity in M. violaceum populations has not been studied.…”

Mating System of the Anther Smut Fungus Microbotryum violaceum : Selfing under Heterothallism

“…Analyses using microsatellites have shown strong heterozygote deficiencies in M. violaceum populations infecting the host S. latifolia (25,39). Further, studies on the meiotic segregation of amplified fragment length polymorphism variation revealed heterozygosity in the genome to be largely restricted to the regions linked to mating type and absent from the autosomes (56).…”

Antagonistic pleiotropy may help population-level selection in maintaining genetic polymorphism for transmission rate in a model phytopathogenic fungus

“…Metapopulations of M. violaceum have been shown to follow an island model dynamics where no isolation by distance can be detected among populations (Delmotte et al, 1999;Giraud, 2004). In our model, a fraction m P ¼ 0.125 of the diseased plants in a given patch send teliospores towards any of the other occupied patches, After among-patch dispersal, probability of extinction is calculated for each occupied patch depending on the total number of plants in a patch (N t ), and the extinction coefficient K ext ¼ 0.9.…”

“…This is likely to be rare as pollinators exhibit a strong preference for healthy plants (Jennersten, 1988;Shykoff and Bucheli, 1995). Furthermore, within-population distributions of M. violaceum spores (Roche et al, 1995) and genotypes (Giraud, 2004) reflect strongly the leptokurtic dispersion, suggesting that mixtures of strains may rarely be deposited on healthy plants. The results of model B imply that it would not be useful to search for an advantage of biased strains in competition situations anyway, and that such advantage, as the slight withinhost competitive advantage of strains with a biased sexratio reported by Hood (2003), would be irrelevant to understand haplo-lethal maintenance.…”