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

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 FIS=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= 39, MAT-B= 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.

诸多生物均可实现后代的共同扩散（codispersal），但能完成相容性配子共同扩散的类群则相对稀少。该扩散机制可提升物种在长距离扩散后的定殖能力，作为一种繁殖保障（reproductive assurance）策略，但同时也会加剧近交（inbreeding）并可能降低种群适合度（fitness）。本研究以粪生黑蛋巢菌（Cyathus stercoreus）为研究对象，该真菌多与粪便或覆盖物伴生，其溅射杯状子实体外观形似迷你鸟巢，内含数千个携带交配相容性减数分裂孢子的“卵”状小包（peridioles）。为解析该物种的遗传结构，研究团队对北美6个城市种群进行分层抽样，并利用10个微卫星标记（microsatellite markers）进行基因分型。研究在4个基因座（loci）中检测到显著的近交信号，表现为杂合子缺失，全局FIS值为0.061。空间自相关分析（spatial autocorrelation）以及通过聚类分析和F统计量（F-statistics）检测到路易斯安那州与密歇根州种群间存在遗传分化，均提示该物种存在扩散限制。尽管近交可能有助于该真菌的定殖，但据估算，近交菌株的生长速率较异交菌株降低15%，这表明近交对种群适合度存在负面影响。交配试验结果显示，粪生黑蛋巢菌的交配型等位基因（mating-type alleles）估算数量（MAT-A=39，MAT-B=24）高于其他鸟巢真菌类群，这将提升其异交效率。我们推测，交配型等位基因数量的增加是该物种近期向城市环境扩张分布范围并扩大种群规模的结果。