Discord in the family Sparidae (Teleostei): divergent phylogeographical patterns across the Atlantic-Mediterranean divide

The Strait of Gibraltar has been proposed to be the divide between two marine biogeographical regions, the Mediterranean Sea and the Northeast Atlantic. Intraspecific studies have shown, for several of the examined species, a reduction of gene flow between the two basins. The present study examines genetic variation at nuclear and mitochondrial loci in five marine teleost species belonging to the family Sparidae. Four samples for each species were analysed spanning the Northeast Atlantic and the Mediterranean. For all individuals 17 allozyme loci were scored and a combined single strand conformation polymorphism-sequencing approach was used to survey approximately 190 bp of the mitochondrial DNA (mtDNA) D-loop region. All five species share similar biological features. For three species, namely Lithognathus mormyrus, Spondyliosoma cantharus, and Dentex dentex, large mtDNA divergence was observed between Atlantic and Mediterranean samples. Little or no mtDNA differentiation was found in the other two species, Pagrus pagrus and Pagellus bogaraveo. Allozyme data revealed strong differentiation when comparing Atlantic and Mediterranean samples of L. mormyrus and D. dentex, moderate for P. pagrus, and no differentiation for P. bogaraveo and S. cantharus. These results provide evidence for a sharp phylogeographical break (sensu Avise) between the Atlantic and the Mediterranean for two (or possibly three) sparid species of the five investigated. At the same time, the obtained results for the other two species raise the question on which ecological/historical factors might have caused the observed discrepancy in the geographical distribution of genetic variation among otherwise biologically similar species.info:eu-repo/semantics/publishedVersio

Establishment of a coastal fish in the Azores : recent colonisation or suddenexpansion of an ancient relict population?

The processes and time scales associated with ocean-wide changes in the distribution of marinespecies have intrigued biologists since Darwin’s earliest insights into biogeography. The Azores, amid-Atlantic volcanic archipelago located more than 1000 km off the European continental shelf,offers ideal opportunities to investigate phylogeographic colonization scenarios. The benthopelagicsparid fish known as the common two-banded seabream (Diplodus vulgaris) is now relativelycommon along the coastline of the Azores archipelago, but was virtually absent prior to the 1990s.We employed a multiple genetic marker approach to test whether the successful establishment of theAzorean population derives from a recent colonization from western continental/island populationsor from the demographic explosion of an ancient relict population.Results from nuclear and mtDNA sequences show that all Atlantic and Mediterranean populationsbelong to the same phylogroup, though microsatellite data indicate significant genetic divergencebetween the Azorean sample and all other locations, as well as among Macaronesian, westernIberian and Mediterranean regions. The results from Approximate Bayesian Computation indicatethat D. vulgaris has likely inhabited the Azores for approximately 40 (95% C.I.: 5.5─83.6) to 52(95% C.I.; 6.32─89.0) generations, corresponding to roughly 80-150 years, which suggests nearcontemporary colonisation, followed by a more recent demographic expansion which could havebeen facilitated by changing climate conditions. Moreover, the lack of previous records of thisspecies over the past century, together with the absence of lineage separation and the presence ofrelatively few private alleles, do not exclude the possibility of an even more recent colonisationevent

Sex change and effective population size : implications for population genetic studies in marine fish

Large variance in reproductive success is the primary factor that reduces effective population size (Ne) in natural populations. In sequentially hermaphroditic (‘sex-changing’) fish, the sex ratio is typically skewed and biased toward the ‘first’ sex, while reproductive success increases considerably after sex change. Therefore, sex-changing fish populations are theoretically expected to have lower Ne than gonochorists (separate sexes), assuming all other parameters are essentially equal. In this study, we estimate Ne from genetic data collected from two ecologically similar species living along the eastern coast of South Africa: one gonochoristic, the ‘santer’ sea bream Cheimerius nufar, and one protogynous (female-first) sex-changer, the ‘slinger’ sea bream Chrysoblephus puniceus. For both species, no evidence of geneticstructuring, nor significant variation in genetic diversity, were found in the study area. Estimates of contemporary Ne were significantly lower in the protogynous species, but the same pattern was not apparent over historical timescales. Overall, our results show that sequential hermaphroditism may affect Ne differently over varying time frames, and that demographic signatures inferred from genetic markers with different inheritance modes also need to be interpreted cautiously, in relation to sex-changing lifehistories

Optimization of single-strand conformation polymorphism and sequence analysis of the mitochondrial control region in Pagellus bogaraveo (Sparidae, Teleostei): Rationalized tools in fish population biology

We report the isolation and sequencing of 400-550 base pairs (bp) of the mitochondrial DNA (mtDNA) control region of eight species of Sparidae (Perciformes, Teleostei). This sequence information allowed us to design specific primers to one of these species (Pagellus bogaraveo). The new set of primers was used to test a rationalized approach to study the mtDNA nucleotide variability at the intraspecific level. The single-strand conformation polymorphism (SSCP) technique was applied to detect sequence variation in two non-overlapping fragments of the control region of 32 individuals of P. bogaraveo. To assess the sensitivity of the method, the nucleotide sequence of the analysed region was determined for all the specimens. The results showed that, for one of the two fragments, SSCP analysis was able to detect 100% of the underlying genetic variability. In sharp contrast, nucleotide variation of the second DNA fragment was completely unresolved by SSCP under different experimental conditions. This suggests that the resolution power of SSCP is crucially dependent on the nature of the fragment subjected to the analysis; therefore, a preliminary test of the sensitivity of the method should be performed on each specific DNA fragment before starting a large-scale survey. A rationalized approach, combining the SSCP technique and a simplified sequencing procedure, is proposed for studying intraspecific polymorphism at the mtDNA control region in fish

Molecular evidence for genetic subdivision of Antarctic krill (Euphausia superba Dana) populations.

Antarctic krill (Euphausia superba Dana) is a key species in the Antarctic food web and occurs on a circumcontinental scale. Population genetic structure of this species was investigated by sequence analysis of the ND1 mitochondrial gene in four population samples collected at different geographical localities around the Antarctic continent. Results indicate the existence of significant genetic differences between samples, and we suggest that oceanographic barriers could be sufficiently strong and temporally stable to restrict gene flow between distinct areas. Moreover, our data indicate that Antarctic krill is not at mutation-drift equilibrium and that the species possibly has a low effective population size as compared to the census size

Genetic differentiation in a pelagic crustacean (Meganyctiphanes norvegica, Euphausiacea), from the North East Atlantic and the Mediterranean Sea

Meganyctiphanes norvegica (M. Sars) is a pe- lagic crustacean that plays a key role in marine food webs of North Atlantic Ocean and marginal seas. We studied eight population samples collected in the Euro- pean Atlantic and Mediterranean Sea. By means of single strand conformation polymorphism analysis (SSCP) and direct sequencing, we investigated a segment of 158 base pairs of the mitochondrial gene coding for the subunit 1 of NADH dehydrogenase. We found 12 sequence variants among the 385 individuals studied. Analysis of molecular variance (AMOVA) showed that 14.75% of the total genetic variability was explained by di\u80erences between populations, thus indicating absence of panmixia for these populations. Pairwise comparisons revealed three distinct genetic pools: the \uaerst one rep- resented by Cadiz Bay, the second one by the Ligurian Sea, and the third one included all the NE Atlantic samples. We also investigated one population from the Alboran Sea (within the Mediterranean basin, east of the Strait of Gibraltar). This population was found to be genetically intermediate between the NE Atlantic sam- ples and the Ligurian sample, suggesting that the restriction to the gene \uafow is not associated with the Strait of Gibraltar, but possibly with the Oran\ub1Almeria oceanographic front. The present work indicates that M. norvegica, although endowed with a high dispersal capacity because of its pelagic habit, can develop sepa- rate breeding units inside the same oceanic basin (the Atlantic). Furthermore, the Ligurian sample should be considered as a distinct evolutionary entity, separated from the Atlantic population

Molecular phylogeny of grey mullets based on mitochondrial DNA sequence analysis: Evidence of a differential rate of evolution at the intrafamily level

The phylogeny of the grey mullets is considered problematic both at the intra- and interfamily level. Such a difficulty arises from the highly homogeneous morphology displayed by this group of fish and, consequently, from the paucity of the key morphological characters suitable to address their phylogeny and evolution. In the present work, we have approached the phylogenetic and evolutionary relationships of seven species of Mugilidae, six of which from the Mediterranean Sea, on the basis of the DNA sequences of two mitochondrial genes (cytochrome b and 12S rRNA). Despite the morphological homogeneity exhibited by the taxa considered, the two species of the genus Mugil (M. cephalus and M. curema) showed a remarkable genetic divergence compared to all the other members of the family. The relative rate test revealed a significantly higher rate of evolution along the Mugil lineage