Extensive Sympatry and Frequent Hybridization of Ecologically Divergent Aquatic Plants on the Qinghai-Tibetan Plateau

Abstract

Hybridization has fascinated biologists in recent centuries for its evolutionary importance, especially in plants. Hybrid zones are commonly located in regions across environmental gradients due to more opportunities to contact and ecological heterogeneity. For aquatic taxa, intrazonal character makes broad overlapping regions in intermediate environments between related species. However, we have limited information on the hybridization pattern of aquatic taxa in alpines, especially submerged macrophytes. In this study, we aimed to test the hypotheses that niche overlap and hybridization might be extensive in related aquatic plants across an altitudinal gradient. We evaluated the niche overlap in three related species pairs on the Qinghai-Tibetan Plateau and assessed the spatial pattern of hybrid populations. Obvious niche overlap and common hybridization were revealed in all three pairs of related aquatic plants. The plateau edge and river basins were broad areas for the sympatry of divergent taxa, where a large proportion of hybrid populations occurred. Hybrids are also discretely distributed in diverse habitats on the plateau. Differences in the extent of niche overlap, genetic incompatibility and phylogeographic history might lead to variation differences in hybridization patterns among the three species pairs. Our results suggested that plateau areas are a hotspot for ecologically divergent aquatic species to contact and mate and implied that hybridization may be important for the freshwater biodiversity of highlands.

Extensive hybridization in Ranunculus section Batrachium (Ranunculaceae) in rivers of two postglacial landscapes of East Europe

“…Interspecific hybridization plays an important role in formation of plant diversity in general [e.g., 17 – 21 ]. In many groups of aquatic plants hybridization is one of the main sources of new, stable, and ecologically important taxa [e.g., 22 – 29 ].…”

“…For the identification of Batrachium , a large set of morphological characteristics should be considered, but in many cases, additional molecular genetic data complemented by karyological and genome size results can be valuable or even necessary. Despite the wide application of molecular marker polymorphisms for the detection and confirmation of hybrids in several aquatic plant groups, this approach is still uncommon in Batrachium 4 , 5 , 10 – 13 , 29 , 30 . This is due to both the poorly known diversity of Batrachium in many regions as well as the underestimation of the role of hybridization and polyploidization in the evolution of the section.…”

Effects of highland environments on clonal diversity in aquatic plants: An interspecific comparison study on the Qinghai-Tibetan Plateau

“…Batrachium comprises three distinct species of hydrophytes on the QTP, while two of them, R. subrigidus and R. trichophyllus , are frequently found across the plateau ( Wang, 2009 ; Chen et al., 2014 ; Wu et al., 2019 ; Wu et al., 2022 ). The two species are both widely distributed across Eurasia and North America, and hybridization between them occurs ( Wiegleb et al., 2017 ; Wu et al., 2022 ). Genetic analysis was performed on their QTP populations by microsatellite markers, and the data were obtained on DRYAD (doi: 10.5061/dryad.gxd2547md).…”

“…The evolutionary histories of aquatic plants in alpine regions have been revealed in some species ( Lu et al., 2016 ; Du and Wang, 2016 ), whereas few of them have focused on the patterns of clonal variation ( Liu et al., 2014 ; Sun et al., 2014 ). Previous studies have implied that the sexual reproduction of aquatic plants in high elevation regions is not rare ( Wang, 2009 ; Wu et al., 2016 ; Wu et al., 2022 ), but there is a lack of comparative studies on multiple species combined with environmental factors.…”

“…Because of twisting branches and invisible underground connections among vegetative structure, it is difficult to distinguish the genets and ramets of aquatic plants through field work. The molecular genotyping data obtained in our previous studies were revisited to evaluate the clonal diversity within populations of relative taxon ( Lu et al., 2016 ; Wu et al., 2019 ; Wu et al., 2020 ; Wu et al., 2022 ). We also measured the local environmental conditions of aquatic habitats and considered climatic factors as ecological variables to model their influences on clonal variation.…”