Abstract
One of the major distinctions of riparian habitats is their linearity. In linear habitats, gene flow is predicted to follow a one-dimensional stepping stone model, characterized by bidirectional gene flow between neighboring populations. Here, we studied the genetic structure of Myricaria germanica, a threatened riparian shrub which is capable of both wind and water dispersal. Our data led us to reject the ‘one catchment – one gene pool’ hypothesis as we found support for two gene pools, rather than four as expected in a study area including four catchments. This result also implies that in the history of the studied populations, dispersal across catchments has occurred. Two contemporary catchment-crossing migration events were detected, albeit between spatially proximate catchments. Allelic richness and inbreeding coefficients differed substantially between gene pools. There was significant isolation by distance, and our data confirmed the one-dimensional stepping-stone model of gene flow. Contemporary migration was bidirectional within the studied catchments, implying that dispersal vectors other than water are important for M. germanica.
Highlights
Riparian habitats host a rich assemblage of specialist plant species confined to floodplains [1]
Our data showed that contemporary gene flow in M. germanica was bidirectional, whereas historic gene flow was directed downstream in the Rhine catchment
Our data rejected the ‘one catchment-one gene pool’ hypothesis, as a single genetic cluster was distributed across four catchments and another one across two
Summary
Riparian habitats host a rich assemblage of specialist plant species confined to floodplains [1]. Linear habitats may function as corridors, facilitating rapid movement of individuals and genes across a landscape [5]. Gene flow is an important process in riparian plant populations because the movement of genes through propagules and gametes ensures connectivity of upstream and downstream populations [6,7]. Gene flow is mediated by seeds, vegetative propagules such as shoots, as well as pollen [8]. Hydrochory, the dispersal of propagules with the water flow of a river, is an important process promoting species richness of riparian habitats [1,9,10]. Water-dispersed propagules are exclusively distributed downstream, and within a given catchment. In insect and wind pollinated species, gene flow via pollen can occur both in upstream and in downstream direction along a river, and across catchments
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