Reticulate evolution in the Crepidomanes minutum species complex (Hymenophyllaceae).
Reticulate evolution in the Crepidomanes minutum species complex (Hymenophyllaceae).
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DOI：
10.3732/ajb.1000484
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发表时间：
2011-11
影响因子：
3
通讯作者：
Joel H. Nitta;A. Ebihara;M. Ito
中科院分区：
文献类型：
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作者：
Joel H. Nitta;A. Ebihara;M. Ito
研究的前提杂交是植物物种形成的一种重要机制，通常导致由多有性二倍体及其杂交后代组成的复合体。然而，这些系统的错综复杂阻碍了对许多群体的透彻了解。小冠蕨科(Hymenophyllaceae)是一种分布广泛、形态多样的蕨类植物复合体。虽然先前关于无配子生殖和多倍体的报告建议进行杂交，但它从来都不是系统发育研究的焦点。方法采用形态、核(GapCp)、叶绿体(RbcL)DNA序列、细胞学、野外观察和孢子计数等方法进行系统发育和杂种起源追踪。主要结果微小隐翅虫物种复合体至少由三个主要分支组成：非洲分支、分支1(东亚和太平洋)和分支2(东南亚和南太平洋)。分支1和分支2在形态变化(在分支1中均匀，而在分支2中高度可变)和杂交种的出现(在分支1中很少，在分支2中频繁)上有显著差异。虽然分支1和分支2之间的遗传距离很大，但仍有几个样本同时含有gapCp序列；在这些样本中，二倍体基因组大小和有性繁殖表明遗传多样性的维持是通过渐渗或不完全的谱系分类，而不是正在进行的杂交。结论细叶锦鸡儿种群复合体是一个由多个二倍体谱系及其稳定的杂交组合组成的网状网络。为了区分二倍体物种和杂交种，还需要对繁殖方式和倍性水平进行额外的取样。
PREMISE OF THE STUDY Hybridization is an important mechanism of speciation in plants and often results in complexes that comprise multiple sexual diploids and their hybrid offspring. However, the intricacy of these systems has prevented a thorough understanding of many groups. The Crepidomanes minutum species complex (Hymenophyllaceae) is a widely distributed, morphologically variable fern species complex. Although prior reports of apogamy and polyploidy suggest hybridization, it has never been the focus of a phylogenetic study. METHODS Morphology, nuclear (gapCp), and chloroplast (rbcL) DNA sequences, cytology, field observation, and spore counts were used to infer phylogeny and trace hybrid origins. KEY RESULTS The C. minutum species complex is composed of at least three major clades: the African clade, clade 1 (East Asia and the Pacific), and clade 2 (Southeast Asia and the South Pacific). Clades 1 and 2 differ strikingly in morphological variation (uniform in clade 1 vs. highly variable in clade 2) and occurrence of hybrids (rare in clade 1 vs. frequent in clade 2). Apogamy and polyploidy were confirmed as likely mechanisms of hybrid stabilization in clade 2. Despite the large genetic distance between clades 1 and 2, several specimens were observed with gapCp sequences from both; diploid genome size and sexual reproduction indicate maintenance of genetic diversity via introgression or incomplete lineage sorting, rather than ongoing hybridization, in these specimens. CONCLUSIONS The C. minutum species complex is a reticulate network including multiple diploid lineages and their stabilized hybrid crosses. Additional sampling focused on reproductive mode and ploidy level is needed to delimit diploid species and hybrids.