Genetische structuur en evolutieve patronen van <i>Pomatoschistus</i> grondels op het Europees Continentaal Plat en in de Middellandse Zee = Genetic structure and evolutionary patterns in <i>Pomatoschistus</i> gobies on the European Continental Shelf and in the Mediterranean Sea

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

Small-scale clinal variation, genetic diversity and environmental heterogeneity in the marine gobies <i>Pomatoschistus minutus</i> and <i>P. lozanoi</i> (Gobiidae, Teleostei)

Genetic variation was assayed at 14 allozyme loci in estuarine, coastal and offshore samples of Lozano's goby, Pomatoschistus lozanoi and the sand goby, P. minutus. Samples were taken from locations on the Belgian Continental Shelf and in the Schelde estuary with a range of environmental heterogeneity. We evaluate whether any differences in (1) the degree of genetic variation and (2) allele frequencies at the various loci exist within samples occurring in various habitats on the BCS and in the Schelde estuary. No significant differences in levels of genetic diversity were recorded between estuarine, coastal and offshore samples in either species. A temporally stable clinal gradient in allele frequencies at the two-allele locus GPI-A* was observed in P. lozanoi, differentiating the samples in an estuarine, coastal and offshore group. We suggest that these differences might be maintained by balancing selection at locus GPI-A*

Allozyme variation and genetic divergence in the sand goby, <i>Pomatoschistus minutus</i> (Teleostei: Gobiidae)

Samples of the widely distributed sand goby Pomatoschistus minutus have been investigated genetically from ten localities in the north-eastern Atlantic, North Sea, western Mediterranean and Adriatic Sea. Levels of genetic diversity and differentiation were assessed with starch (SGE) and cellulose acetate (CAGE) gel electrophoresis for 13 enzyme systems. Genetic differentiation between spatial samples points to a reduction or even absence of gene flow between the Adriatic and the other samples, including the western Mediterranean Sea (pair-wise FST=0·37 and 0·32 for SGE and CAGE respectively). The sample from the Adriatic Sea was clearly differentiated from the other samples at the lactate dehydrogenase loci LDH-A* (SGE and CAGE) and LDH-C* (CAGE). Values for genetic differentiation between Venetian and other sand gobies were of the same order of magnitude as between P. minutus and its closest relative P. lozanoi, suggesting allopatric speciation in the lagoon of Venice. At locations outside the Adriatic Sea, the sand goby has the typical features of a marine fish with a high level of gene flow and a low degree of genetic differentiation

Allozyme variation and genetic divergence in the sand goby, <i>Pomatoschistus minutus</i> (Teleostei: Gobiidae)

Samples of the widely distributed sand goby Pomatoschistus minutus have been investigated genetically from ten localities in the north-eastern Atlantic, North Sea, western Mediterranean and Adriatic Sea. Levels of genetic diversity and differentiation were assessed with starch (SGE) and cellulose acetate (CAGE) gel electrophoresis for 13 enzyme systems. Genetic differentiation between spatial samples points to a reduction or even absence of gene flow between the Adriatic and the other samples, including the western Mediterranean Sea (pair-wise FST=0·37 and 0·32 for SGE and CAGE respectively). The sample from the Adriatic Sea was clearly differentiated from the other samples at the lactate dehydrogenase loci LDH-A* (SGE and CAGE) and LDH-C* (CAGE). Values for genetic differentiation between Venetian and other sand gobies were of the same order of magnitude as between P. minutus and its closest relative P. lozanoi, suggesting allopatric speciation in the lagoon of Venice. At locations outside the Adriatic Sea, the sand goby has the typical features of a marine fish with a high level of gene flow and a low degree of genetic differentiation

Subtle genetic differentiation in a high gene flow marine species (<i>Pomatoschistus minutus</i>) living in a dynamic environment

We assessed genetic differentiation and diversity in 15 populations of sand goby (Pomatoschistus minutus) within the Southern Bight of the North Sea, using seven microsatellite and thirteen allozyme loci. While no significant differentiation was observed with allozymes, microsatellite loci revealed a moderate level of differentiation (overall FST=0.026; overall RST=0.058). The hierarchical analysis of molecular variance revealed a significant differentiation (pST and RST) of differentiation lead us to conclude that this genetic structure was mainly due to an historical event, namely colonisation of the estuary during its establishment, and to restricted actual gene flow. Therefore, using all of these loci, we found that the 15 natural populations of the sand goby can be clustered into two different breeding units, namely the Oosterschelde and coastal populations. Despite this clear distinction, there were indications of an actual complex dynamic local structure that would bear further examination to understand the processes involved in the differentiation of these two breeding units