Arctic-alpine distributions--metapopulations on a continental scale?

Cold-adapted species in the Northern Hemisphere frequently show arctic-alpine discontinuous ranges at high latitudes and on mountains farther south, but area connectivity through current and historical gene flow remains unclear. We used the coalescent-based program IMa (Isolation with Migration-analytic) to test for migration among disjunct European areas of arctic-alpine wolf spiders of the Pardosa saltuaria group. Mitochondrial (ND1) and nuclear (ITS1, 5.8S rDNA, ITS2) markers were analyzed simultaneously. Gene flow was unidirectional from Scandinavia to the Alps and the Carpathians, complex with respect to intermediate relict areas in central Europe, and very limited in outlying areas in the Balkans and Pyrenees. Population connectivity may have been greater during glacial events that might alternatively account for the inferred arctic-alpine links. A simulation study under various demographic histories (using a new module in the Mesquite package, which models episodic migration) showed that the empirical results are equally consistent with moderate levels of ongoing (continuous) migration or, alternatively, with strong migration bursts at the last glacial maximum but not at earlier times. Habitat connectivity was probably maximal during glacial events, illustrating the potential influence of ecology and life history on organismal responses to past climatic change.