The influence of oceanographic fronts and early-life-history traits on connectivity among littoral fish species.

The spatial distribution of neutral genetic diversity is mainly influenced by barriers to dispersal. The nature of such barriers varies according to the dispersal means and capabilities of the organisms concerned. Although these barriers are often obvious on land, in the ocean they can be more difficult to identify. Determining the relative influence of physical and biotic factors on genetic connectivity remains a major challenge for marine ecologists. Here, we compare gene flow patterns of 7 littoral fish species from 6 families with a range of early-life-history traits sampled at the same geographic locations across common environmental discontinuities in the form of oceanic fronts in the Western Mediterranean. We show that these fronts represent major barriers to gene flow and have a strong influence on the population genetic structure of some fish species. We also found no significant relation between the early-life-history traits most commonly investigated (egg type, pelagic larval duration, and inshore-offshore spawning) and gene flow patterns, suggesting that other life-history factors should deserve attention. The fronts analyzed and the underlying physical mechanisms are not site-specific but common among the oceans, suggesting the generality of our findings.

Rapid radiation and cryptic speciation in mediterranean triplefin blennies (Pisces: Tripterygiidae) combining multiple genes.

The genus Tripterygion is the unique genus of the family Tripterygiidae in the Mediterranean Sea and in the northeastern Atlantic coast. Three species and four subspecies had been described: Tripterygion tripteronotus and Tripterygion melanurus (T. m. melanurus and T. m. minor) are endemic of the Mediterranean, and T. delaisi (T. d. delaisi and T. d. xanthosoma) is found in both areas. We used five different genes (12S, 16S, tRNA-val, COI, and 18S) to elucidate their taxonomy status and their phylogenetic relationships. We employed different phylogenetic reconstructions that yielded different tree topologies. This discrepancy may be caused by the speciation process making difficult the reconstruction of a highly supported tree. All pair comparisons between these three species showed the same genetic divergence indicating that the speciation process could have been resolved by a rapid radiation event after the Messinian Salinity Crisis (5.2Mya) leading to a trichotomy. Our molecular data revealed two clearly supported clades within T. tripteronotus, whose divergence largely exceeded that found between other fish species, consequently these two groups should be considered two cryptic species diverging 2.75-3.32Mya along the Pliocene glaciations. On the contrary, none of the genes studied supported the existence of two subspecies of T. melanurus. Finally, the two subspecies of T. delaisi were validated and probably originated during the Quaternary climatic fluctuations (1.10-1.23Mya), however their distribution ranges should be redefined.