Contrasts in genetic structure and historical demography of marine and riverine populations of Atherina at similar geographical scales

In this paper, we compare the genetic structure and the historical demography of two populations of the sand smelt Atherina boyeri from the rivers Tagus and Mondego (Portugal) with two groups of samples of the closely related marine Atherina presbyter collected on the shore at comparable latitudes. A. presbyter is a pelagic marine inshore fish, while A. boyeri is typically found in coastal lagoons, estuaries and freshwaters bodies. Analysis of mtDNA control region sequences showed that the marine A. presbyter did not display signs of genetic differentiation between sites some hundreds of kilometers apart. On the contrary, A. boyeri showed clear differences between populations. The populations of A. boyeri showed a much lower genetic diversity and younger coalescence times when compared with A. presbyter. We suggest that these differences reflect the interplay between differences in ecology between the two species and the historical impact of the glaciations. While A. presbyter likely moved to the south evading the cold periods, A. boyeri probably went extinct and its populations in Western Europe are recent recolonizations from western Mediterranean refugia.