Repeated homoploid hybrid speciation (HHS) events with the same parental species have rarely been reported. In this study, we used population transcriptome data to test paraphyly and HHS events in the conifer Picea brachytyla. Our analyses revealed non-sister relationships for two lineages of P. brachytyla, with the southern lineage being placed within the re-circumscribed P. likiangensis species complex (PLSC) and P. brachytyla sensu stricto (s.s.) consisted solely of the northern lineage, forming a distinct clade that is paratactic to both the PLSC and P. wilsonii. Our phylogenetic and coalescent analyses suggested that P. brachytyla s.s. arose from HHS between the ancestor of the PLSC before its diversification and P. wilsonii through an intermediate hybrid lineage at an early stage and backcrossing to the ancestral PLSC. Additionally, P. purpurea shares the same parents and an extinct lineage with P. brachytyla s.s. but backcrossing to the other parent, P. wilsonii at a later stage. We reveal the first case that backcrossing to different parents of the same extinct hybrid lineage produced two different hybrid species. Our results highlight the existence of more reticulate evolution during species diversification in the spruce genus and more complex homoploid hybrid events than previously identified.

与相同亲本物种重复发生的同倍体杂交物种形成（HHS）事件很少有报道。在这项研究中，我们使用群体转录组数据来测试针叶树云杉的并系发育和 HHS 事件。我们的分析揭示了P. brachytyla两个谱系的非姐妹关系，其中南部谱系被置于重新划定的P. likiangensis物种复合体 (PLSC) 内，而P. brachytyla sensu stricto (ss) 仅由北部谱系组成，形成一个与 PLSC 和P. wilsonii并列的独特分支。我们的系统发育和聚结分析表明，P. brachytyla ss 起源于分化之前的 PLSC 祖先和P. wilsonii之间的 HHS ，通过早期的中间杂交谱系并与祖先 PLSC 回交。此外，P. purpurea与P. brachytyla ss具有相同的亲本和已灭绝的谱系，但在后期与另一个亲本P. wilsonii回交。我们揭示了第一个案例，即与同一灭绝杂交谱系的不同亲本回交产生了两个不同的杂交物种。我们的结果强调了云杉属物种多样化过程中存在更多的网状进化，以及比之前发现的更复杂的同倍体杂交事件。