Large-scale and small-scale genetic patterns in three species of marine gobies, Pomatoschistus minutus (Pallas, 1770), P. lozanoi (de Buen, 1923) and P. microps (Kroyer, 1838) were studied. We used the available knowledge of the biology of the species and past and present-day oceanographic features throughout their distributional range for inferring population genetic structure and phylogeographical history of small demersal fish species along the European coasts. These three species occur sympatrically throughout a large part of their distributional range, which comprises the European Atlantic coasts and the Mediterranean Sea. They have a similar potential for dispersal with an extended pelagic larval stage, but differ ecologically. Small-scale patterns along the Belgian coast were studied with allozyme electrophoresis at fourteen putative loci. No evidence for population differentiation was found, except for a clinal change in allele frequencies at one locus in P. lozanoi. We suggest that this is due to differential selective pressure in distinct habitats (resp. estuarine, coastal and marine), rather than reproductive isolation. Contrary to other studies, we did not find any correlation between environmental heterogeneity and levels of genetic diversity. For studying large-scale genetic structure we employed a combination of allozyme electrophoresis, SSCP- and sequence analysis of fragment of the cytochrome b locus on the mtDNA. Overall patterns of P. minutus and P. microps revealed (1) the highest amount of divergence between Atlantic and Mediterranean species, (2) a pattern of isolation-by-distance, consistent with a larval dispersal via oceanic currents and (3) a shallow phylogeographical structure with a few common (ancestral) haplotypes and a large number of rare variants radiating. In the Atlantic basin, phylogeographical analysis of both species points to a range expansion into northern areas with a loss of variation at higher latitudes and a possible glacial refugium in the English Channel or the Southem Bight. However, despite similar overall patterns, striking interspecific differences were recorded. P. microps is much more differentiated than P. minutus on the same scale, and has a different phylogeographical history in the Mediterranean Sea. We suggest that this is due to ecological constraints on dispersal in the estuarine-marine P. microps. We postulate that species-specific behavioural patterns play a more important role in shaping population structure than usually accounted for. |
