Effects of peripherality and hybridization on range-wide genetic structure of the coastal dune plant Abronia umbellata (Nyctaginaceae)
Van Natto, Alyson
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The pattern of genetic variation across a species range may give insight into geographic variation in adaptive capacity and hence, conservation priority. For this reason, determining the factors that may influence range-wide genetic structure is vital, but remains relatively understudied. Demography has long been viewed as the dominant factor influencing species’ genetic structure, but non-demographic processes must be considered as well. In this study, we investigated the effects of peripherality, hybridization and mating system on the range wide genetic structure of Abronia umbellata, a pink-flowered Pacific coastal dune endemic and that ranges from San Quintin, Baja California to Coos Bay, Oregon and occurs as disjunct populations in Washington and on Vancouver Island in Canada. The species exhibits striking mating system differentiation across the range with obligately outcrossing populations south of San Francisco and highly selfing populations to the north. Abronia umbellata also has two congeners that it co-occurs and creates putative phenotypic hybrids with, yellow-flowered A. latifolia and magenta-flowered A. maritima. Genetic analyses of sequence variation at nine single-copy genes revealed that outcrossing and selfing populations of A. umbellata are genetically differentiated from each other and northern disjunct populations of A. umbellata are genetically similar to selfing populations. Furthermore, the northern disjunct populations contain little unique variation and thus, likely arose through a recent long-distance dispersal event or fragmentation of a recent expansion. Southern edge populations in Baja California, on the other hand, are genetically unique and significantly higher in genetic variation than other outcrossing populations. Extensive searches in 37 populations across the range of A. umbellata in 2017 and 2018, revealed that phenotypic hybrids occurred in 100% of locations where outcrossing populations of A. umbellata were sympatric with a congener and sequence variation at five single-copy genes indicate that phenotypic hybrids are in fact hybrids. However, during the same searches we did not find any phenotypic hybrids with selfing populations of A. umbellata and quantitative analyses showed that hybrids were only found in 2.6% of 695 3-m radius plots across all 37 populations.