The speciation and adaptation of the polyploids: a case study of the Chinese Isoetes L. diploid-polyploid complex

Background The ChineseIsoetesL. are distributed in a stairway pattern: diploids in the high altitude and polyploids in the low altitude. The allopolyploidI. sinensisand its diploid parentsI. yunguiensisandI. taiwanensisis 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. yunguiensiswith partial populations of theI. sinensisandI. taiwanensiswith the rest populations of theI. sinensis. The crow node of theI. sinensisallopolyploid system was 4.43 Ma (95% HPD: 2.77-6.97 Ma). The divergence time betweenI. sinensisandI. taiwanensiswas estimated to 0.65 Ma (95% HPD: 0.26-1.91 Ma). The narrower niche breadth inI.sinensisthan those of its diploid progenitors and less niche overlap in the pairwise comparisons between the polyploid and its progenitors. Conclusions Our results elucidate thatI. yunguinensisandI. taiwanensiscontribute to the speciation ofI. 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 ofI. sinensis. Additionally, niche novelty of the allopolyploid population ofI. sinensishas 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.