Taking the common into account: phylogeographical patterns of native, non-endemic plant species of the Canary Islands

Abstract

Abstract Islands sustain an outstanding proportion of Earth´s biodiversity. However, modern molecular studies on oceanic island floras have typically focused on endemics, which leaves many research questions involving other types of taxa unaddressed. In this study, we analyze the patterns of genetic variation in two co-occurring native non-endemics (NNE) that are common components of lowland habitats across the Canarian archipelago: Launaea arborescens (Asteraceae), a wind-dispersed species, and Lycium intricatum (Solanaceae), an endozoochorus species. We predicted that, given their presumably recent colonization of the archipelago, both lineages should show a genetic pattern compatible with a stepping-stone model, i.e. from the easternmost islands (closest to mainland Africa) to the western islands. We carried out exhaustive sampling in all the islands of distribution and in neighbouring mainland areas (SW Morocco). Using three plastid DNA regions, we calculated levels of haplotype diversity, conducted analyses of spatial distribution of molecular variance, and tested various models of colonization and gene flow with complementary coalescent-based approaches. For comparison, we additionally performed a literature review to assess general patterns of haplotype diversity on plant species with similarly widespread distributions across the archipelago. A stepping-stone model of island colonization was only partly supported by our results, since back-colonization of mainland areas was a scenario equally supported by coalescent analyses and estimates of historical gene flow. Both species showed that the easternmost islands represented de facto a genetic continuum of the neighbouring mainland area. However, Lycium generally displayed much higher rates of gene flow than Launaea, which may be due to secondary dispersal mediated by predatory birds. Lastly, our literature survey revealed that both NNE harbour unprecedented high levels of genetic diversity on the easternmost Canary islands. This study illustrates that the phylogeographical analysis of NNE provides novel insights into island biogeography, since these taxa can deviate from common patterns observed in endemic lineages.