The impact of ecological factors on natural hybridization is of widespread interest. Here, we asked whether climate niche influences hybridization between the two closely related plant species Myriophyllum sibiricum and M. spicatum. Eight microsatellite loci and two chloroplast fragments were used to investigate the occurrence of hybridization between these two species in two co-occurring regions: north-east China (NEC) and the QinghaiTibetan Plateau (QTP). The climate niches of the species were quantified by principal component analysis with bioclimatic data, and niche comparisons were performed between the two species in each region. Reciprocal hybridization was observed, and M. sibiricum was favoured as the maternal species. Furthermore, hybrids were rare in NEC but common in the QTP. Accordingly, in NEC, the two species were climatically distinct, and hybrids only occurred in the narrow geographical or ecological transition zone, whereas in the QTP, obvious niche overlaps were found for the two species, and hybrids occurred in multiple contact zones. This association between hybridization pattern and climate niche similarity suggests that the level of hybridization was promoted by niche overlap. Compared with the parental species, similar climate niches were found for the hybrid populations in the QTP, indicating that other environmental factors rather than climate were important for hybrid persistence. Our findings highlight the significance of climate niche with respect to hybridization patterns in plants.

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Quaternary climatic oscillation had a significant role in the patterns of geographic distribution and genetic structure of plants occurring in Qinghai-Tibet Plateau (QTP) and adjacent areas. In this study, we examined the phylogeographical structure of Typha laxmannii in the northeast QTP and adjacent areas based on 15 populations and 148 individuals using sequences of chloroplast rpl32-trnL and nuclear phytochelatin synthase gene. Two chloroplast haplotypes and eight nuclear haplotypes were found. All haplotypes were shared and no private haplotype was fixed in plateau populations. The genetic diversity of the populations in adjacent areas based on chloroplast DNA and nuclear DNA was four and two times greater than that of plateau populations, respectively. Genetic differentiation among plateau populations, which mainly existed between the eastern and western populations, was higher than that among adjacent areas. Our results indicate that the present patterns of genetic diversity and genetic structure of T. laxmannii in the northeast QTP and its adjacent areas were caused by postglacial recolonization from at least two refugia to plateau platform and a resulting founder effect.