Mature habitats associated with genetic divergence despite strong dispersal ability in an arthropod

Background  

Populations may be bound by contemporary gene flow, selective sweeps, and extinction-recolonization processes. Indeed, existing molecular estimates indicate that species with low levels of gene flow are rare. However, strong priority effects and local selective regimes may hinder gene flow (despite dispersal) sending populations on independent evolutionary trajectories. In this scenario (the monopolization hypothesis), population differentiation will increase with time and genealogical evidence should yield ample private haplotypes. Cyclical parthenogens (e.g. rotifers and cladocerans such as Daphnia) have an increased capacity for rapid local adaptation and priority effects because sexual reproduction is followed by multiple generations of clonal selection and massive egg bank formation. We aimed to better understand the history of population differentiation and ongoing gene flow in Daphnia rosea s.l., by comparing population and regional divergences in mature unglaciated areas and younger previously glaciated areas. We also examined the timing and paths of colonization of previously-glaciated areas to assess the dispersal limitations of D. rosea s.l. We used DNA sequence variation (84 populations and >400 individuals) at the mitochondrial ND2 and nuclear HSP90 loci from Holarctic populations for our genetic analyses.