Data from: Evolution and reciprocal origins in Mediterranean ferns: the Asplenium obovatum and A. adiantum-nigrum complexes

Asplenium is estimated to be the largest fern genus, and is very prone to polyploidy and hybridization. We investigated the phylogenetic relationships of two geographically-restricted complexes in the Mediterranean Basin, and searched for evidence of multiple and/or reciprocal origins of the allopolyploids. The Asplenium obovatum and A. adiantum-nigrum complexes include a total of five diploid and four polyploid taxa, and are linked by the tetraploid A. balearicum. We collected 36 new samples representing all nine taxa, from which we amplified 5 chloroplast regions. We also included sequences from GenBank and performed ML and BI analyses to identify multiple and reciprocal origins. We conducted a larger molecular dating analysis to assess relationships with the rest of Asplenium and estimate divergence times. This matrix included 137 species of Asplenium and three outgroups, including sequences previously published. All sequences of allotetraploids A. adiantum-nigrum and A. balearicum grouped with A. onopteris, with no sign of reciprocal parentage, but possible evidence of multiple origins. The tetraploids A. foreziense and A. billotii grouped with both respective parents, indicating probable multiple and reciprocal origins. The best supported case of reciprocal parentage is A. foreziense. In the larger analysis, the species studied resolve in two different clades that correspond to the two complexes, and the groups are not closely related, with a conservative estimate of 45.43 Mya for their divergence. There is evidence of multiple origins of all four allopolyploids, though only with strong support for one, and of reciprocal origins for two of the four allopolyploids, though again only one is well supported. A. balearicum represents a hybridization event between members of clades whose ancestors diverged roughly 45 million years ago, making this divergence one of the oldest to have descendants later produce hybrid offspring.

铁角蕨属（Asplenium）被认为是物种最为丰富的蕨类植物属，该类群极易发生多倍化与杂交事件。本研究针对地中海盆地中两个地理局限分布的类群复合体开展了系统发育关系解析，并对异源多倍体的多次独立起源及双向亲本起源证据进行了检索。卵叶铁角蕨（Asplenium obovatum）复合体与黑柄铁角蕨（Asplenium adiantum-nigrum）复合体共计包含5个二倍体类群与4个多倍体类群，二者通过四倍体巴利阿里铁角蕨（Asplenium balearicum）形成关联。本研究采集了覆盖全部9个类群的36份全新样本，对其中5个叶绿体基因区域进行了扩增；同时纳入基因银行（GenBank）中的公开序列数据，通过最大似然法（ML）与贝叶斯推断法（BI）开展系统发育分析，以验证多次独立起源与双向亲本起源假说。我们还开展了更大规模的分子定年分析，以明确该属类群与铁角蕨属其余类群的系统发育关系，并估算其分化时间。该分析矩阵涵盖137种铁角蕨属植物及3个外类群，所用序列均为已发表的公开数据。所有异源四倍体物种黑柄铁角蕨与巴利阿里铁角蕨的序列均与欧铁角蕨（Asplenium onopteris）聚为同一支系，未发现双向亲本起源的直接证据，但存在多次独立起源的潜在线索。四倍体物种佛氏铁角蕨（Asplenium foreziense）与比洛特铁角蕨（Asplenium billotii）则分别与其两个亲本类群聚为一支，表明其可能存在多次独立且双向的亲本起源，其中佛氏铁角蕨的双向亲本起源证据支持度最高。在更大规模的分析中，本次研究的类群分别归入对应两个复合体的不同支系，二者亲缘关系较远；保守估算显示，两个支系的分化时间约为4543万年前。本研究结果为4种异源多倍体均存在多次独立起源提供了支撑，不过仅1个类群得到了较强的统计支持；同时也为其中2个异源多倍体存在双向亲本起源提供了依据，同样仅1个类群获得了较好的支持强度。巴利阿里铁角蕨的杂交事件发生于两个分化支系的祖先类群之间，二者的分化时间约为4500万年前，这使其成为迄今已知的、祖先支系分化时间最久远且后续仍能产生杂交后代的案例之一。