Data from: Interploidal hybridization and mating patterns in the Sphagnum subsecundum complex

Polyploidization is thought to result in instant sympatric speciation, but several cases of hybrid zones between one of the parental species and its polyploid derivative have been documented. Previous work showed that diploid Sphagnum lescurii is an allopolyploid derived from the haploids S. lescurii (maternal progenitor) and S. subsecundum (paternal progenitor). Here we report the results from analyses of a population where allodiploid and haploid S. lescurii co-occur and produce sporophytes. We tested (1) whether haploids and diploids form hybrid triploid sporophytes, (2) how hybrid and non-hybrid sporophytes compare in fitness, (3) whether hybrid sporophytes form viable spores, (4) the ploidy of any viable gametophyte offspring from hybrid sporophytes, (5) the relative viability of sporelings derived from hybrid and non-hybrid sporophytes, and (6) if interploidal hybridization results in introgression between the allopolyploid and its haploid progenitor. We found that triploid hybrid sporophytes do occur and are larger than non-hybrid sporophytes, but exhibit very low germination percentages and produce sporelings that develop more slowly than those from non-hybrid sporophytes. All sporophytes attached to haploid gametophytes were triploid and were sired by diploid males, but all sporophytes attached to diploid gametophytes were tetraploid. This asymmetric pattern of interploidal hybridization is related to an absence of haploid male gametophytes in the population. Surprisingly, all sporelings from triploid sporophytes were triploid, yet were genetically variable, suggesting some form of aberrant meiosis that warrants further study. There was limited (but some) evidence of introgression between allodiploid and haploid S. lescurii.多倍体化（Polyploidization）被认为会引发瞬时同域物种形成（sympatric speciation），但已有多项研究记录了某一亲本物种（parental species）与其多倍体衍生类群（polyploid derivative）之间存在杂交带（hybrid zones）。此前研究表明，二倍体莱斯泥炭藓（Sphagnum lescurii）是由单倍体莱斯泥炭藓（母本祖先，maternal progenitor）与亚扁泥炭藓（S. subsecundum，父本祖先，paternal progenitor）形成的异源多倍体（allopolyploid）。本研究针对一处同时存在异源二倍体（allodiploid）与单倍体莱斯泥炭藓并可产生孢子体（sporophytes）的种群展开分析，现将结果报道如下：我们开展了六项验证实验：(1) 单倍体与二倍体是否可形成杂交三倍体（triploid）孢子体；(2) 杂交孢子体与非杂交孢子体的适合度（fitness）存在何种差异；(3) 杂交孢子体能否产生具有活力的孢子；(4) 杂交孢子体所产生的可育配子体（gametophyte）后代的倍性（ploidy）如何；(5) 杂交与非杂交孢子体所产生的孢子幼苗（sporelings）的相对活力水平；(6) 倍间杂交是否会导致该异源多倍体与其单倍体祖先类群之间发生基因渐渗（introgression）。研究发现，三倍体杂交孢子体确实存在，且其体型大于非杂交孢子体，但萌发率极低，所产生的孢子幼苗的生长速率也慢于非杂交孢子体来源的幼苗。所有附着于单倍体配子体的孢子体均为三倍体，且由二倍体雄配子体授精；而所有附着于二倍体配子体的孢子体均为四倍体（tetraploid）。这种不对称的倍间杂交模式与种群中缺乏单倍体雄配子体密切相关。令人意外的是，所有来自三倍体孢子体的孢子幼苗均为三倍体，但遗传背景存在差异，这提示存在某种形式的异常减数分裂（aberrant meiosis），有待进一步研究。此外，我们仅获得了有限（但确实存在）的证据，证明异源二倍体与单倍体莱斯泥炭藓之间发生了基因渐渗。