Island biogeography through the lens of bryophytes: insights and future perspectives

Abstract

In the last years we have seen a fascinating progression in the knowledge of how evolutionary and ecological processes shape biodiversity on islands, but also how insular biotas interact with continental biological assemblages. However, distinguishing among processes that can take place over different timescales but causing similar genetic signatures has remained problematic. In this respect, cuttingedge analytical tools based on (phylo)genetic and species distribution modeling have brought unprecedented insights into the mechanisms governing community assemblage. These technical advances have challenged the view of oceanic islands as evolutionary deadends, which had been built on typical insular syndromes such as the loss of dispersal capacities, to recently emphasize the role of oceanic islands as hotspots of endemism and glacial refugia for continental reverse colonization. Here we investigate whether such a paradigm holds for extremely mobile organisms, using bryophyte species that are disjunct between the Macaronesian archipelagos and continental regions as a model. We thus use bryophytes to: investigate, at the population level, oceanic island continental relationships at the scale of an entire biogeographic region; reconstruct the geographical origin of the colonization of Macaronesian by bryophytes; and explore whether low levels of oceanic island endemism in bryophytes as compared to angiosperms can be explained by fast rates of continental colonization following an islanddriven speciation event. We show that demographic and phylogeographic patterns in bryophytes can significantly depart from those observed in other plant groups like angiosperms. In sharp contrast with the classical island theory, these findings therefore indicate that oceanic islands may be a key source of biodiversity for continental regions.