Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA.
Heredity (Edinb). 2013 Apr;110(4):355-62. doi: 10.1038/hdy.2012.95. Epub 2012 Nov 21.
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.
许多生物表现出后代的共分散，但较少表现出相容配子的共分散。这种机制增强了物种在长距离扩散后殖民的能力，作为一种生殖保证机制，但它也促进了近亲繁殖和潜在的适应度降低。在这里，我们研究了鸟类巢穴真菌 Cyathus stercoreus 的长距离扩散和近亲繁殖，这是一种与粪便和覆盖物相关的真菌，其 splash cup 果实体看起来像微型鸟类巢穴的“卵”或 peridioles，其中包含数千个交配相容的减数分裂孢子。为了研究该物种的遗传结构，我们对六个北美的城市种群进行了层次抽样，并使用 10 个微卫星标记进行了基因型分析。我们在四个位点检测到了显著的近交程度，通过杂合子缺失检测到 FIS=0.061。扩散限制既可以通过空间自相关来推断，也可以通过聚类和 F 统计数据检测路易斯安那州和密歇根州之间的种群结构来推断。尽管近亲繁殖可能有助于真菌的殖民化，但它对种群的适应度有负面影响，从自交菌株的生长速度相对于杂交菌株降低 15%来估计。交配测试表明，C. stercoreus 比其他鸟类巢穴真菌具有更高的估计交配型等位基因数（MAT-A=39，MAT-B=24），这将提高其异交效率。我们推测，交配型等位基因数量的增加是由于最近在城市环境中种群范围和大小的扩张所致。
