Hybridization in bryophytes involves a fusion of gametes produced by haploid parental gametophytes of different species. The primary hybrid is thus the short-lived diploid sporophyte, which soon undergoes meiosis prior to the formation of large amounts of haploid spores. We compared morphology of gametophytes (branch leaves) and sporophytes (capsule inclination) from sympatric populations and allopatric populations of H. lutescens and H. sericeum. In addition, we used transcriptome data to select 85 nuclear SNP markers that were fixed for alternative alleles in the two species. The SNPs were used to estimate the degree of hybridization in diploid sporophytes. Our study shows that gametophytes from sympatric populations display intermediate morphology in a number of leaf characters, with exception for leaf sizes, which are markedly smaller than those in allopatric populations. None of the 100 sporophytes appeared to be primary hybrids, but 33 displayed admixing—heterozygotic expression of SNP markers or mismatch of occasional markers in homozygous condition—suggesting that extensive introgression takes place in the sympatric populations. Most sporophytes with intermediate capsule inclination, initially classed as putative hybrids, did not display admixture of nuclear SNP markers. Sixty-seven percent of admixed sporophytes have predominantly nuclear SNPs typical for H. lutescens. Our results suggest that interspecific hybridization and bidirectional introgression are relatively common in the studied sympatric populations, giving rise to viable recombinants, but not complete mixing of the parental genomes. Our study is one of the first detailed accounts of hybridization among pleurocarpous mosses, opening for future studies of gene transfer and introgression between bryophyte lineages and its role in local adaptation and long-term evolutionary diversification.

中文翻译：

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形态特征和 SNP 标记表明在同域群落中存在杂交和基因渗入的胸膜苔藓 Homalothecium lutescens 和 H. sericeum

苔藓植物中的杂交涉及由不同物种的单倍体亲本配子体产生的配子的融合。因此，初级杂种是短寿命的二倍体孢子体，它在形成大量单倍体孢子之前很快经历减数分裂。我们比较了来自 H. lutescens 和 H. sericeum 的同域种群和异域种群的配子体（分枝叶）和孢子体（荚膜倾角）的形态。此外，我们使用转录组数据选择了 85 个核 SNP 标记，这些标记针对两个物种中的替代等位基因进行了固定。SNP 用于估计二倍体孢子体的杂交程度。我们的研究表明，来自同域种群的配子体在许多叶片特征中显示出中间形态，但叶片大小除外，它们明显小于异域种群。100 个孢子体中没有一个似乎是初级杂种，但 33 个表现出混合——SNP 标记的杂合表达或纯合条件下偶尔标记的错配——表明在同域种群中发生了广泛的基因渗入。大多数具有中间荚膜倾向的孢子体，最初被归类为假定的杂种，没有显示出核 SNP 标记的混合物。67% 的混合孢子体主要具有 H. lutescens 的典型核 SNP。我们的结果表明，种间杂交和双​​向基因渗入在所研究的同域种群中相对常见，产生可行的重组体，但不能完全混合亲本基因组。