Next generation biogeography: raft spiders as a model lineage

Historical biogeography is an integrative scientific field critical for testing evolutionary hypotheses pertinent to organismal distributions, but despite recent theoretical and analytical advances, biogeographic reconstructions continue to struggle with accuracy and rigor. Most modern studies include the three elements needed for historical biogeographic inference, namely a time-calibrated phylogeny, contemporary taxonomic distributions, and estimations of organismal dispersal probabilities. The latter are, for the most part, particularly vague, and historical biogeography would greatly benefit from dispersal probability estimations that are better informed, thus accounting for a) organismal dispersal biology; b) organismal ecology; c) geological histories; and d) geographical factors. We term this novel concept next-generation biogeography. Due to their old age and mega-diversity—considering both phylogenetic and lifestyle diversity—spiders are an ideal animal group for modern biogeographic research. Within our project (BIORAFTS), we will demonstrate the relevance and feasibility of next-generation biogeography on a global lineage of semi-aquatic arthropods, the raft spiders (also fishing spiders, genus Dolomedes, Pisauridae). This genus contains over a hundred flamboyant, large spider species that inhabit freshwater bodies and terrestrial habitats on most continents, where they prey upon large invertebrates and even vertebrates. Although rather big and conspicuous, many Dolomedes species are elusive, living a hidden predatory life at the water's edge. Taxonomy and phylogeny of the group are still poorly known and many species new to science are awaiting description. BIORAFTS will address these taxonomic and phylogenetic deficiencies in our knowledge, then test historical biogeographical hypotheses explaining the phylogenetic timing and the geographic origin of raft spiders’ ancestor, and explore subsequent global colonization of Dolomedes species as well as the genus’ diversification on major land masses. We will explain the absence of raft spiders in South America and contribute to the taxonomic understanding of Dolomedes elsewhere, notably in Madagascar. Within the proposed four work packages we will employ integrative research and outreach thereby training one competent predoctoral and one postdoctoral researcher. Through outreach, we will promote the importance of biogeography specifically, and of biodiversity and conservation in general. Our next-generation biogeography is a novel concept that will help further develop the approaches and tools available to reconstruct the biogeography of any organism. Importantly, our project will link the past with the future, allowing new predictions of biotic reactions to rapid global changes in climate and habitat.