Reconstructing ancient dispersal through Antarctica: A case study of stream-inhabiting beetles

Abstract

Aim: Although Antarctica hosted a diverse fauna and flora in the past, its modern climate is too extreme for many lineages: their recent extinction makes it difficult to include the continent in historical biogeographical analyses. We use southern temperate stream-inhabiting beetles as a model to explore whether Antarctica may be included in historical biogeographic reconstructions in a group absent from Antarctica today, and to test its role in shaping the current distribution of stream-inhabiting insects. Taxon: Coleoptera, Elmidae. Location: Southern Hemisphere temperate regions and Antarctica. Methods: We included Antarctica in historical biogeographic analyses indirectly, as a component of distance matrices specifying the relative positions of continents, or by specifying Antarctica as a stepping-stone between remaining continents (in LEMAD). We used a newly constructed dated phylogeny of Elmidae to test the performance of these constrained analyses under different parameter settings and geographical scenarios. Results: Antarctica can be implemented into historical biogeographic analyses via indirect constraints to produce biologically relevant reconstructions when long-distance dispersal events are highly penalized, the maximum number of areas per species is low, and expected extinction rates are high (in LEMAD). Unconstrained models, including those without Antarctica, result in simpler scenarios with fewer biogeographic events and better fit to data. The origin of austral clades of Elmidae post-date the separation of Gondwanan landmasses. Main Conclusions: Antarctica can be included in historical biogeographic reconstructions under a priori assumptions that (1) it was part of the ancient biogeography of the clade, (2) the taxon has limited dispersal ability, making long-distance dispersal highly unlikely and (3) maximum range size is limited. These assumptions may be biologically justified for many animal groups. Over-water dispersal has been crucial in shaping the modern distribution of austral stream-inhabiting beetles, likely facilitated by ocean currents and dispersal through Antarctica until the Oligocene.