Inbreeding depression in urban environments of the bird’s nest fungus Cyathus stercoreus (Nidulariaceae: Basidiomycota)

Abstract

Many organisms display codispersal of offspring, but fewer display codispersal of compatible gametes. This mechanism enhances the ability of a species to colonize after long distance dispersal as a mechanism of reproductive assurance, but it also fosters inbreeding and potential reduction in fitness. Here we investigated both long distance dispersal and inbreeding in the bird's nest fungus Cyathus stercoreus, a dung and mulch-associated fungus with a splash cup fruiting body appearing like a miniature bird's nest of 'eggs' or peridioles that contain thousands of mating compatible meiotic spores. To investigate the genetic structure in the species, six North American urban populations were hierarchically sampled and genotyped using 10 microsatellite markers. We detected significant levels of inbreeding through heterozygote deficiencies at four loci, with global F IS ¼ 0.061. Dispersal limitation was suggested by both spatial autocorrelation and the detection of population structure between Louisiana and Michigan using clustering and F-statistics. Although inbreeding may facilitate colonization by the fungus, it has a negative effect on the fitness of populations as estimated from a 15% reduction in growth rates of inbred strains relative to outcrossed. Mating tests revealed that C. stercoreus has a higher estimated number of mating-type alleles (MAT-A ¼ 39, MAT-B ¼ 24) than other species of bird's nest fungi, which would increase its outcrossing efficiency. We speculate that the increased number of mating-type alleles is the result of a recent range and population size expansion into urban environments.

How the truffle got its mate: insights from genetic structure in spontaneous and planted Mediterranean populations of Tuber melanosporum

“…Species where meiotic spores from the same zygote are dispersed together and where mating thereafter occurs among spatially close haploids undergo high inbreeding, as described in Microbotryum violaceum (Giraud et al . ) and Cyathus stercoreus (Malloure & James ). Yet, given its predominantly haploid life cycle where diploidy is transient (Fig.…”

Population structure of an orchid mycorrhizal fungus with genus-wide specificity

“… 5 ). Generally, saprotrophic mushrooms have randomly mating populations, but inbreeding is shown increasingly in various mushrooms ranging from the ectomycorrhizal fungus Laccaria amethystina 43 , the saprophytic mushrooms Trogia venenata 44 and the bird’s nest fungus Cyathus stercoreus 45 . Although further investigation is required to determine whether Tulasnella has a bipolar or tetrapolar mating system, the high levels of inbreeding detected in this study suggest a few mating types only in T .…”