用核DNA和叶绿体DNA序列鉴别铁线蕨属Adiantum L.(凤尾蕨科)新的隐性杂交种

A new cryptic hybrid species of Adiantum L.(Pteridaceae) identified by nuclear and chloroplast DNA sequences

物种自然杂交现象在自然界中普遍存在,并被认为在适宜条件下可以多地独立发生.2013年,在云南元江采集的7种铁线蕨属植物中,其中一种在形态上疑似台湾产梅山铁线蕨,而该种被认为是以假鞭叶铁线蕨为母本、半月形铁线蕨为父本的自然杂交物种.形态学比较显示,该存疑种与铁线蕨属其他种类均有明显差别,用单拷贝核DNA序列CRY2exon 3和叶绿体DNA序列rbc L,atp B,atp A,trn L-F,rps4-trn S对云南元江产梅山铁线蕨存疑种进行研究,结果显示云南元江产梅山铁线蕨存疑种为以苍山铁线蕨为母本和以孟连铁线蕨为父本的自然杂交种,由于形态上与台湾产梅山铁线蕨相似、父母本亲缘关系上与梅山铁线蕨的双亲近缘,因而可称为梅山铁线蕨的隐性杂交种.据此认为,中国可能存在大量的自然杂交种尚未发现,并可以通过核DNA序列和叶绿体DNA序列进行准确鉴定;同时,诸如铁线蕨属这样的蕨类植物,由于存在无性繁殖习性,可以弥补有性生殖隔离带来的适合度降低的缺陷,增加杂交种在自然界中的存活机会,是蕨类植物中自然杂交种普遍存在的重要原因.

Natural hybridization has been commonly found in ferns and is generally believed to happen independently at different locations if the range of the parent species overlaps. In 2013, we collected seven species of Adiantum from Yuanjiang, Yunnan, China. The identity of one of these collections remained in doubt; the plant is very similar to A. meishanianum （A. malesianum ×A. philippense）, a natural hybrid from Taiwan, China. Morphological comparison showed that this unidentified collection was different from other related taxa. Sequencing of a single copy of an exon （CRY2 exon 3） of the nuclear genome suggested this plant contained haplotype sequences of both A. sinicum and A. menglianense. Therefore, it should be treated as a new hybrid. Phylogenic analysis based on five chloroplast DNA sequences （rbcL, atpB, atpA, trnL-F and rps4-trnS） indicated that the plant was clustered in A. sinicum, which could be considered to be the female parent of the hybrid. This new hybrid is not only similar to A. meishanianum in morphology, but also its parental taxa are in sister groups in the phylogeny. Hence, the new hybrid was considered to be a cryptic hybrid species. Our methods could be extended to identify other potential natural fern hybrids in China. The habit of clonal propagation potentially occurs in nature, so this natural hybrid could easily survive in the field because clonal growth can offset the lack of fitness caused by sexual reproductive isolation, which may be an important reason why so many hybrid ferns exist in nature.