Phylogeography of Aphanius fasciatus (Osteichthyes: Aphaniidae) in the Mediterranean Sea,with a focus on its conservation in Cyprus

Hydrobiologia - Aphanius fasciatus is a small fish occurring in Mediterranean brackish environments. In Cyprus it is known from three localities separated by long stretches of coast. The genetic...     

Spatial genetic patterns of Octopus vulgaris Mediterranean populations support the hypothesis of a transitional zone across the Siculo-Tunisian Strait

Hydrobiologia - Recent research hypothesised that the Siculo-Tunisian Strait might fit, at least for some species, the picture of a genetic transitional zone instead of a sharp genetic break...     

A complex species complex: The controversial role of ecology and biogeography in the evolutionary history of Syllis gracilis Grube, 1840 (Annelida,Syllidae)

The cryptic diversity in the polychaete Syllis gracilis Grube, 1840, in the Mediterranean Sea was examined with an integrative morpho-molecular approach. Individuals of S. gracilis were collected at eleven Mediterranean localities to provide an insight into the role of brackish environments in inducing cryptic speciation. The examination of morphological features combined with a molecular genetic analysis based on a partial sequence of the 16S rRNA gene highlighted discrepancies between morphological and molecular diversity. Morphological data allowed to identify a morphotype with short appendages occurring in coralline algae communities and another one with long appendages observed in brackish-water environments and Sabellaria reefs. Multivariate analyses showed that sampling localities were the greatest source of morphological divergence, suggesting that phenotypic plasticity may play a role in local adaptations of S. gracilis populations. Molecular data showed the occurrence of four divergent lineages not corresponding to morphological clusters. Different species delimitation tests gave conflicting results, retrieving, however, at least four separated entities. Some lineages occurred in sympatry and were equally distributed in marine and brackish-water environments, excluding a biogeographic or ecological explanation of the observed pattern and suggesting instead ancient separation between lineages and secondary contact. The co-occurrence of different lineages hindered the identification of the lineage corresponding to S. gracilis sensu stricto. The discrepancy between morphological and molecular diversity suggests that different environmental and biogeographic features may interact in a complex and unpredictable way in shaping diversity patterns. An integrative approach is needed to provide a satisfactory insight on evolutionary processes in marine invertebrates.     

Multilocus Comparative Phylogeography of Two Aristeid Shrimps of High Commercial Interest (Aristeus antennatus and Aristaeomorpha foliacea) Reveals Different Responses to Past Environmental Changes

Phylogeographical studies can reveal hidden patterns in the evolutionary history of species. Comparative analyses of closely related species can further help disentangle the relative contributions of processes responsible for such patterns. In this work, the phylogeography of two aristeid species, Aristeus antennatus and Aristaeomorpha foliacea, was compared through multiple genetic markers. These marine shrimp species are of high commercial importance, and are exploited in the Mediterranean Sea (MED) and in Mozambique Channel (MOZ) where they occur in partial sympatry. Aristeus antennatus (N = 50) from Western and Eastern Mediterranean (WM and EM, respectively), Atlantic Ocean (AO) and MOZ, and Aristaeomorpha foliacea (N = 40) from WM, EM, MOZ North-Western Australia (AUS) were analyzed with two nuclear genes (PEPCK and NaK) and one mitochondrial (COI) gene. Within the study area differences were found between the two species in their phylogeographical patterns, suggesting distinct responses to environmental changes. Monophyly of Aristeus antennatus was found across its distributional range. This pattern contrasted by a deep evolutionary split within Aristaeomorpha foliacea where genetic diversity followed geography distinguishing MED-MOZ and AUS. We propose that the AUS lineage of A. foliacea warrants consideration as a distinct species, with consequent implications in systematics and resource management.     

A preliminary investigation of allozyme genetic variation and population geographical structure in Aphanius fasciatus from Italian brackish-water habitats

A total of 150 individuals from Aphanius fasciatus from coastal brackish-water habitats was analysed by allozyme electrophoresis to collect data on its genetic variation. From 22 enzymes, 43 putative enzyme-coding loci were resolved, 12 of which were polymorphic at P_0·99 level. Only one of the 31 probability tests showed a significant departure from the Hardy-Weinberg equilibrium. Aphanius fasciatus showed low levels of genetic polymorphism, with expected heterozygosity values ranging from 0·027 (S.E.=0·013) to 0·064 ( s.e. =0·023). Nei's genetic distances between populations ranged from 0·002 to 0·042. Weir & Cockerham F -statistics showed high levels of genetic heterogeneity among populations (jackknifed θ=0·302, s.e. =0·045) and estimates of N _m were < 1, indicating restricted gene flow. Significant positive correlation between genetic distance and geographical distance matrices, detected by Mantel's test ( g =1·941; P 0·001), is consistent with the prediction that the species is genetically structured by isolation-by-distance.     

Temporal Genetic Variation in a Population of Aphanius fasciatus (Cyprinodontidae) from a Brackish-water Habitat at Elba Island (Italy)

Allozyme electrophoresis was used to assess temporal genetic variation in three successive generations of the Mediterranean killifish, Aphanius fasciatus. Samplings were carried out in 1995, 1996 and 1997 in a brackish-water habitat at Elba Island, Italy and a total of 212 specimens were collected. The five loci for which polymorphism has been detected in a previous study were assayed. Mean expected heterozygosity values [H=0.397 (SE 0.077), H=0.336 (SE 0.092) and H=0.313 (SE 0.092) in 1995, 1996 and 1997, respectively] were not significantly different by ANOVA test. Deviations from Hardy–Weinberg equilibrium were minimal, with only one out of the 15 probability tests showing a significant departure from the equilibrium; whereas genotypic linkage disequilibrium was not detected. Values of Nei's genetic distance were lower than 0.04. Temporal genetic variation in the A. fasciatus population at Elba Island was observed, with F-statistics indicating significant genetic divergence among samples (=0.035, SE 0.027, p<0.001). Genetic drift acting on two loci (GPD-1 ^* and LDH-3 ^*) is presumably the main force determining the temporal genetic heterogeneity observed; however, the occurrence of selection on individual loci and/or sampling error cannot be excluded. The observed allelic variation among generations in a single population of A. fasciatus is much less than levels observed among geographically discrete samples in previous studies.     

Analysis of genetic variability in Aristaeomorpha foliacea (crustacea, aristeidae) using DNA-ISSR (Inter Simple Sequence Repeats) markers

This work reports the first genetic data of Aristaeomorpha foliacea, a marine decapod of high commercial value, from six Mediterranean localities and one new fishing ground in the Mozambique Channel. The use of five Inter Simple Sequence Repeat (ISSR) primers provided 150 polymorphic loci. Average estimates of genetic diversity did not significantly differ among sampled localities, with a mean value of heterozygosity H = 0.105 ± 0.015. Analysis of molecular variance (AMOVA) allocated > 98% of genetic variability to the within-sample component, displaying values higher than those previously reported in ISSR studies on marine invertebrates. Cluster analyses did not detect geographically or genetically distinct groups. The observed lack of large-scale genetic differentiation is discussed in relation to the high potential for larval dispersal of the species and to features of the marker employed.     

Mitochondrial DNA variability of the pipefish Syngnathus abaster

This study provides data on the genetic structuring of the pipefish Syngnathus abaster in the western Mediterranean and Adriatic Seas. A total of 109 specimens were collected in brackish‐water biotopes. The control region and three other regions of the mitochondrial genome were analysed. The most relevant result was the high genetic structuring found by Bayesian inference (BI), maximum likelihood (ML) and network analyses, which were consistent in showing three well‐separated clusters of S. abaster populations. Furthermore, BI and ML did not support the monophyly of the taxon S. abaster. These results suggest the occurrence of a species complex in the study area, whose differentiation may have occurred since the Pleistocene. The results also show a very high genetic variability at the inter‐population level, with no shared haplotypes among sites. Evolutionary forces due to the fragmented nature of the brackish‐water habitats may account for the high genetic divergence found among the groups and populations. Finally, although dispersal by rafting over long distances may occasionally occur, this study suggests linear stepping‐stone model of colonization to be most likely. The complexity of the results obtained suggests that further studies are needed to elucidate the phylogeny of S. abaster.     

Fine-grained spatial genetic structure in the bivalve Gemma gemma from Maine and Virginia (USA), as revealed by Inter-Simple Sequence Repeat markers

Gemma gemma is a small ovoviviparous bivalve distributed in shallow sand flats along the North American Atlantic and Gulf of Mexico coasts. Genetic variation in G. gemma was analysed by means of Inter-Simple Sequence Repeats (ISSRs) at the following levels: (i) between localities (Maine and Virginia), (ii) among 10-m-diameter patches within localities, and (iii) within patches. Thirty individuals/patch and three patches/locality were analysed. Individuals were genotyped for 67 ISSR polymorphic loci from five primers. The portion of the genetic variation found between localities (2%) was small compared to that found either among patches within localities (37%) or within patches (61%). ISSRs in G. gemma allowed the detection of significant differentiation at individual and patch levels. By contrast, a low degree of genetic variability was found between localities. The small-scale genetic heterogeneity does not follow a simple, consistent pattern. Our results contrast with the generally accepted rule that aplanic species are locally homogeneous and globally heterogeneous and teleplanic species are the inverse.     

Does the Mediterranean killifish Aphanius fasciatus (Teleostei: Cyprinodontidae) fit the one-dimensional stepping-stone model of gene flow?

Five samples (30 individuals each) of the Mediterranean cyprinodontid fish, Aphanius fasciatus, were analysed by allozyme electrophoresis for a study concerning genetic structure and gene flow among populations. Forty-three loci, twelve of which were polymorphic at P_0.99 level, were analysed. A. fasciatus showed low levels of genetic polymorphism, with expected heterozygosity values ranging from 0.027 (SE = 0.013) to 0.064 (SE = 0.023). The modified Rogers' genetic distances ranged from 0.053 to 0.202. The observed pattern of genetic differentiation among populations, obtained by multidimensional scaling of the modified Rogers' genetic distances, was consistent with geographic distribution. Coancestry coefficient ( = 0.302, SE = 0.045) indicated a very high degree of genetic subdivision among populations and the estimate of gene flow (the effective number of migrants per generation, Nm = 0.445), computed by Wright's method, showed very restricted gene flow among populations. The regression analysis carried out using log-transformed values of geographic distance against M^ (pairwise values of Nm) gave a regression coefficient, b = –1.03, indicating that a restricted migration rate among populations can occur according to the one-dimensional stepping-stone model. The amount and modality of gene flow in A. fasciatus inferred from the results of the present study are consistent with the absence of dispersal stages and with the fragmented nature of brackish-water habitats along the coasts.