Data from: 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 expected heterozygosity at the population level. Polyandry was frequent, on average 59% of the sporophytes on a female shoot were sired by distinct fathers. In conclusion, sporadic fertilizations by dwarf males originating from nonhost female shoots appear to counteract strong inbreeding.附生于雌株的矮雄体，为解决苔藓植物受精距离过短的难题提供了可行方案。然而，尖峰态的孢子扩散模式会让矮雄体与其宿主枝丛的亲缘关系极为紧密，由此带来近交风险。雌株能够容纳大量不同基因型的矮雄体，这暗示苔藓可能存在拮抗近交的机制，例如多父本交配（polyandry）与受精后选择。 我们对金灰藓（Homalothecium lutescens）四个种群的孢子体（sporophyte）、雌宿主枝丛与矮雄体进行了基因分型（genotype）。未发现基于杂合性水平开展选择性孢子体败育的证据。在其中三个种群中，完全纯合的孢子体与显著为正的近交系数（inbreeding coefficient）同时出现，且平均FIS值介于0.48至0.64之间，这表明母子交配事件频发。 不过，所有采样孢子体中约23%的杂合性水平高于种群平均预期杂合性。多父本交配现象较为普遍：平均而言，雌株枝丛上59%的孢子体由不同父本授精。 综上，源自非宿主雌株枝丛的矮雄体所介导的偶发受精，似乎能够抵消强烈的近交效应。