The speciation and adaptation of the polyploids: a case study of the Chinese Isoetes L. diploid-polyploid complex
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RESEARCH ARTICLE
Open Access
The speciation and adaptation of the polyploids: a case study of the Chinese Isoetes L. diploid-polyploid complex Xiaokang Dai1, Xiang Li1, Yuqian Huang1 and Xing Liu1,2*
Abstract Background: The Chinese Isoetes L. are distributed in a stairway pattern: diploids in the high altitude and polyploids in the low altitude. The allopolyploid I. sinensis and its diploid parents I. yunguiensis and I. taiwanensis is an ideal system with which to investigate the relationships between polyploid speciation and the ecological niches preferences. Results: There were two major clades in the nuclear phylogenetic tree, all of the populations of polyploid were simultaneously located in both clades. The chloroplast phylogenetic tree included two clades with different populations of the polyploid clustered with the diploids separately: I. yunguiensis with partial populations of the I. sinensis and I. taiwanensis with the rest populations of the I. sinensis. The crow node of the I. sinensis allopolyploid system was 4.43 Ma (95% HPD: 2.77–6.97 Ma). The divergence time between I. sinensis and I. taiwanensis was estimated to 0.65 Ma (95% HPD: 0.26–1.91 Ma). The narrower niche breadth in I.sinensis than those of its diploid progenitors and less niche overlap in the pairwise comparisons between the polyploid and its progenitors. Conclusions: Our results elucidate that I. yunguinensis and I. taiwanensis contribute to the speciation of I. sinensis, the diploid parents are the female parents of different populations. The change of altitude might have played an important role in allopolyploid speciation and the pattern of distribution of I. sinensis. Additionally, niche novelty of the allopolyploid population of I. sinensis has been detected, in accordance with the hypothesis that niche shift between the polyploids and its diploid progenitors is important for the establishment and persistence of the polyploids. Keywords: Allopolyploid, Altitude, Chinese Isoetes, Distribute pattern, Niche breadth, Niche novelty
Background Polyploidy, or whole-genome duplication (WGD), is widespread in plants, fungi and animals [1–3]. Allopolyploidy and autopolyploidy are the two ways to duplicate chromosomal materials: the former one originates from a hybridization of two species with associated genome duplication while the latter one results from genome duplication within one species [4–6]. WGD is one of the * Correspondence: [email protected] 1 Laboratory of Plant Systematics and Evolutionary Biology, College of Life Sciences, Wuhan University, Wuhan 430072, Hubei, People’s Republic of China 2 College of Sciences, Tibet University, Lhasa 850012, Tibet, People’s Republic of China
most important forces for vascular plant evolution [7]. Nearly 25% of vascular plants are recent polyploids [7], and more than 15% of angiosperm species and 30% of ferns are estimated to be polyploids through speciation [8]. Additionally, an ancient WGD event occurring in flowering plants is hypothesized to have catalysed key innovations that led to t
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