Balance between inbreeding and outcrossing in a nannandrous species, the moss Homalothecium lutescens

Epiphytic dwarf males on the females present a possible solution to the problem of short fertilization distances in mosses. However, leptokurtic spore dispersal makes dwarf males likely to be closely related to their host shoot, with an accompanying risk of inbreeding. The capacity of a female to harbour a high number of different dwarf males suggests that there may be mechanisms in place that counteract inbreeding, such as polyandry and post-fertilization selection. We have genotyped sporophytes, female host shoots and dwarf males in four populations of the moss Homalothecium lutescens. We found no evidence of selective sporophyte abortion based on level of heterozygosity. The occurrence of entirely homozygous sporophytes together with significantly positive inbreeding coefficients in three of the populations (mean FIS between 0.48 and 0.64) suggest frequent mother–son mating events. However, 23% of all sampled sporophytes had a higher level of heterozygosity compared with the mean exp...附生矮雄个体（epiphytic dwarf males）为苔藓植物解决受精距离（fertilization distances）过短的难题提供了潜在可行方案。然而，尖峰态孢子扩散（leptokurtic spore dispersal）会使矮雄个体与其宿主枝亲缘关系紧密，进而伴随近交（inbreeding）风险。雌株可容纳大量不同矮雄个体的特性，提示存在抵消近交的相关机制，例如多雄交配（polyandry）与受精后选择（post-fertilization selection）。我们对4个金灰藓（*Homalothecium lutescens*）种群的孢子体（sporophytes）、雌株宿主枝（female host shoots）及矮雄个体（dwarf males）开展了基因分型（genotyped）研究。未发现基于杂合度（heterozygosity）水平选择性孢子体败育的证据。全纯合孢子体的出现，加之其中3个种群的近交系数（inbreeding coefficients）显著为正（平均FIS值介于0.48至0.64之间），表明母子交配事件（mother–son mating events）频发。然而，所有采样孢子体中23%的个体杂合度水平高于平均预期值