Department of Biology & L. E. Anderson Bryophyte Herbarium, Duke University, Durham, NC, 27708, USA.
Pennsylvania Natural Heritage Program, Western Pennsylvania Conservancy, Pittsburgh, PA, 15222, USA.
Ann Bot. 2023 Oct 4;132(1):77-94. doi: 10.1093/aob/mcad077.
Sphagnum (peatmoss) comprises a moss (Bryophyta) clade with ~300-500 species. The genus has unparalleled ecological importance because Sphagnum-dominated peatlands store almost a third of the terrestrial carbon pool and peatmosses engineer the formation and microtopography of peatlands. Genomic resources for Sphagnum are being actively expanded, but many aspects of their biology are still poorly known. Among these are the degree to which Sphagnum species reproduce asexually, and the relative frequencies of male and female gametophytes in these haploid-dominant plants. We assess clonality and gametophyte sex ratios and test hypotheses about the local-scale distribution of clones and sexes in four North American species of the S. magellanicum complex. These four species are difficult to distinguish morphologically and are very closely related. We also assess microbial communities associated with Sphagnum host plant clones and sexes at two sites.
Four hundred and five samples of the four species, representing 57 populations, were subjected to restriction site-associated DNA sequencing (RADseq). Analyses of population structure and clonality based on the molecular data utilized both phylogenetic and phenetic approaches. Multi-locus genotypes (genets) were identified using the RADseq data. Sexes of sampled ramets were determined using a molecular approach that utilized coverage of loci on the sex chromosomes after the method was validated using a sample of plants that expressed sex phenotypically. Sex ratios were estimated for each species, and populations within species. Difference in fitness between genets was estimated as the numbers of ramets each genet comprised. Degrees of clonality [numbers of genets/numbers of ramets (samples)] within species, among sites, and between gametophyte sexes were estimated. Sex ratios were estimated for each species, and populations within species. Sphagnum-associated microbial communities were assessed at two sites in relation to Sphagnum clonality and sex.
All four species appear to engage in a mixture of sexual and asexual (clonal) reproduction. A single ramet represents most genets but two to eight ramets were dsumbers ansd text etected for some genets. Only one genet is represented by ramets in multiple populations; all other genets are restricted to a single population. Within populations ramets of individual genets are spatially clustered, suggesting limited dispersal even within peatlands. Sex ratios are male-biased in S. diabolicum but female-biased in the other three species, although significantly so only in S. divinum. Neither species nor males/females differ in levels of clonal propagation. At St Regis Lake (NY) and Franklin Bog (VT), microbial community composition is strongly differentiated between the sites, but differences between species, genets and sexes were not detected. Within S. divinum, however, female gametophytes harboured two to three times the number of microbial taxa as males.
These four Sphagnum species all exhibit similar reproductive patterns that result from a mixture of sexual and asexual reproduction. The spatial patterns of clonally replicated ramets of genets suggest that these species fall between the so-called phalanx patterns, where genets abut one another but do not extensively mix because of limited ramet fragmentation, and the guerrilla patterns, where extensive genet fragmentation and dispersal result in greater mixing of different genets. Although sex ratios in bryophytes are most often female-biased, both male and female biases occur in this complex of closely related species. The association of far greater microbial diversity for female gametophytes in S. divinum, which has a female-biased sex ratio, suggests additional research to determine if levels of microbial diversity are consistently correlated with differing patterns of sex ratio biases.
泥炭藓（泥炭藓）由约 300-500 种苔藓植物组成。该属具有无与伦比的生态重要性，因为泥炭藓占主导地位的泥炭地储存了近三分之一的陆地碳库，并且泥炭藓塑造了泥炭地的形成和微地形。泥炭藓的基因组资源正在得到积极扩展，但它们的许多生物学特性仍然知之甚少。其中包括泥炭藓物种无性繁殖的程度，以及这些以单倍体为主的植物中雌雄配子体的相对频率。我们评估了北美四种大磁石复合物物种的克隆性和配子体性别比，并测试了关于克隆和性别的局部尺度分布的假设。这四种物种在形态上难以区分，并且非常密切相关。我们还评估了两个地点与泥炭藓宿主植物克隆体和性别的相关微生物群落。
对代表 57 个种群的 405 个四个物种样本进行了限制位点相关 DNA 测序（RADseq）。基于分子数据的种群结构和克隆性分析同时利用了系统发育和表型方法。使用 RADseq 数据识别多基因座基因型（基因）。使用一种分子方法确定采样的配子体的性别，该方法利用了在使用表现出性别表型的植物样本验证该方法后，性染色体上的位点的覆盖范围。估计了每个物种的性别比，并估计了种内和种群内的性别比。通过每个基因组成的分株数量来估计遗传之间的适应度差异。在种内、种间和配子体性别之间估计了克隆度[基因数/分株数（样本）]。估计了每个物种的性别比，并估计了种内和种群内的性别比。在两个地点评估了与泥炭藓克隆性和性别相关的泥炭藓相关微生物群落。
所有四个物种似乎都进行了有性和无性（克隆）繁殖的混合。单个分株代表了大多数基因，但也检测到一些基因有两个到八个分株。只有一个基因在多个种群中存在分株；所有其他基因都局限于一个种群。在种群内，单个基因的分株在空间上聚集在一起，表明即使在泥炭地内扩散也有限。在 S. diabolicum 中，性别比偏向雄性，但在其他三个物种中偏向雌性，尽管在 S. divinum 中差异显著。物种和雄性/雌性之间没有克隆繁殖的差异。在圣雷吉斯湖（纽约）和富兰克林沼泽（佛蒙特州），站点之间的微生物群落组成存在强烈差异，但未检测到物种、基因和性别之间的差异。然而，在 S. divinum 中，雌性配子体拥有的微生物类群数量是雄性配子体的两到三倍。
这四个泥炭藓物种都表现出相似的繁殖模式，这些模式是有性和无性繁殖混合的结果。基因克隆复制的分株的空间模式表明，这些物种介于所谓的 phalanx 模式和 guerrilla 模式之间，在 phalanx 模式中，基因相互邻接，但由于分株碎片有限，不会广泛混合，而在 guerrilla 模式中，广泛的基因碎片和扩散导致不同基因的混合更多。尽管在苔藓植物中性别比通常偏向雌性，但在这个密切相关的物种复合体中，也存在雄性和雌性偏向。在具有雌性偏向性别比的 S. divinum 中，雌性配子体与更大的微生物多样性相关联，这表明需要进一步研究以确定微生物多样性水平是否与不同的性别比偏向模式一致。
