Browsing by Author "Bernardi, Giacomo"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
- Historical colonization and demography of the Mediterranean damselfish, Chromis chromisPublication . Domingues, Vera dos Santos; Bucciarelli, Giuseppe; Almada, Vítor Carvalho; Bernardi, GiacomoThe desiccation of the Mediterranean Sea during the Messinian Salinity Crisis 6.0–5.3 million years ago (Ma), caused a major extinction of the marine ichthyofauna of the Mediterranean. This was followed by an abrupt replenishment of the Mediterranean from the Atlantic after the opening of the Strait of Gibraltar. In this study, we combined demographic and phylogeographic approaches using mitochondrial and nuclear DNA markers to test the alternative hypotheses of where (Atlantic or Mediterranean) and when (before or after the Messinian Salinity Crisis) speciation occurred in the Mediterranean damselfish, Chromis chromis. The closely related geminate transisthmian pair Chromis multilineata and Chromis atrilobata was used as a way of obtaining an internally calibrated molecular clock. We estimated C. chromis speciation timing both by determining the time of divergence between C. chromis and its Atlantic sister species Chromis limbata(0.93–3.26 Ma depending on the molecular marker used, e.g. 1.23–1.39 Ma for the control region), and by determining the time of coalescence for C. chromis based on mitochondrial control region sequences (0.14–0.21 Ma). The time of speciation of C. chromis was always posterior to the replenishment of the Mediterranean basin, after the Messinian Salinity Crisis. Within the Mediterranean, C. chromis population structure and demographic characteristics revealed a genetic break at the Peloponnese, Greece, with directional and eastbound gene flow between western and eastern groups. The eastern group was found to be more recent and with a faster growing population (coalescent time = 0.09–0.13 Ma, growth = 485.3) than the western group (coalescent time = 0.13–0.20 Ma, growth = 325.6). Our data thus suggested a western origin of C. chromis, most likely within the Mediterranean. Low sea water levels during the glacial periods, the hydrographic regime of the Mediterranean and dispersal restriction during the short pelagic larval phase of C. chromis(18–19 days) have probably played an important role in C. chromis historical colonization.
- Phylogenetic analysis of peri-mediterranean blennies of the genus Salaria: Molecular insights on the colonization of freshwatersPublication . Almada, Vítor Carvalho; Robalo, Joana Isabel; Levy, André; Freyhof, J.; Bernardi, Giacomo; Doadrio, IgnacioIn this paper, the phylogenetic relationships of the marine blenny Salaria pavo and the freshwater S. fluviatilis and S. economidisi were analyzed using four molecular markers: the mitochondrial 12S rRNA, 16S rRNA, and the control region and the nuclear first intron of the S7 ribosomal protein. The monophyly of Salaria is supported, as well as that of S. pavo and that of all the freshwater members of Salaria. Thus, the present results support a single origin for all freshwater Mediterranean blenniids. Our results reject the placement of the species of Salaria in the genus Lipophrys as proposed in previous studies. Using a molecular clock calibrated with trans-Isthmian geminate blenniid species, the split between the ancestor of the freshwater lineage and the ancestor of S. pavo is tentatively placed in the Middle Miocene (well before the Messinian). The marine S. pavo displays a very low level of intraspecific sequence divergence consistent with a Pleistocene bottleneck. S. fluviatilis is a paraphyletic entity with S. economidisi nested within it. A Moroccan population of S. fluviatilis is more divergent than S. economidisi, both in nuclear and mitochondrial genes. Fish from Israel together with some Turkish samples represent the second oldest split. It is argued that these populations may represent cryptic species. Thus, further studies on the taxonomy of these freshwater blennies are urgently needed.
- Phylogeography and evolution of the triplefin Tripterygion delaisi (Pisces, Blennioidei)Publication . Domingues, Vera dos Santos; Almada, Vítor Carvalho; Santos, Ricardo Serrão; Brito, Alberto; Bernardi, GiacomoThe genus Tripterygion (Risso 1826) is restricted to the eastern Atlantic and the Mediterranean, and comprises only three species. T. melanuros and T. tripteronotus are essentially endemic to the Mediterranean, while Tripterygion delaisi occurs in the Atlantic and in the Mediterranean. Two subspecies of T. delaisi have been described (T. d. xanthosoma in the Mediterranean and T. d. delaisi in the Atlantic). Several scenarios have been proposed for the evolution of T. delaisi subspecies, but so far its subspeciation process is not clear. In this study we present a population survey of T. delaisi including specimens from the two recognized subspecies. We combined a phylogeographic approach with estimates of the direction of migration (between the Atlantic and the Mediterranean) and of the coalescence time of the two subspecies, using polymorphic mitochondrial and nuclear genes. The results of this study clearly support the existence of two Tripterygion delaisi clades, one in the eastern Atlantic islands and another in the Atlantic coasts of Europe and in the Mediterranean. Historical migration between the islands and Western Europe plus Mediterranean was restricted, and showed a westbound trend, with a higher number of migrants going from the Western Europe plus Mediterranean into the islands. We estimated the time of coalescence of both groups of T. delaisi to be more recent than the onset of Pleistocene glaciations (1.7 Mya). Our results are consistent with previous hypothesis that consider successive dispersal events of a Tripterygion ancestor from the western African coast colonizing the Atlantic islands and the Mediterranean, promoting the evolutionary divergence between these areas.
- Tropical fishes in a temperate sea: Evolution of the wrasse Thalassoma pavo and the parrotfish Sparisoma cretense in the Mediterranean and the adjacent Macaronesian and Cape Verde ArchipelagosPublication . Domingues, Vera dos Santos; Alexandrou, Markos; Almada, Vítor Carvalho; Robertson, D. Ross; Brito, Alberto; Santos, Ricardo Serrão; Bernardi, GiacomoThe northeastern Atlantic and the Mediterranean Sea share geological histories and display great faunal affinities. The majority of the Mediterranean species have Atlantic origins, with a few species with tropical affinities. These include the parrotfish Sparisoma cretense and the wrasse Thalassoma pavo that are restricted to the subtropical northeastern Atlantic, the Macaronesian archipelagos (Azores, Madeira, and Canaries) and the southern Mediterranean. The Pleistocene glaciations have been described as having different effects on the fauna of the two regions. During glacial peaks, Mediterranean waters remained warmer than those of the adjacent Atlantic. Within the eastern Atlantic, the effects of Pleistocene glaciations were differentiated. Here, we perform a comparative analysis focusing on T. pavo and S. cretense populations from the northeastern Atlantic and the Mediterranean to assess the effects of Pleistocene glaciations in these two species. Sequences from the mitochondrial control region were obtained and analyzed combining phylogeographic and demographic approaches. Gene flow between Atlantic and Mediterranean populations was shown to be very high. The Mediterranean populations of T. pavo and S. cretense showed high levels of genetic diversity, even in the eastern basin, pointing to an ancient colonization event. This suggests that both species must have been able to persist in the Mediterranean during the cold Pleistocene periods. Historical migration estimates revealed a Mediterranean towards Atlantic trend in the case of T. pavo, which may reflect the re-colonization of areas in the Atlantic by fish that survived the cold phases in relatively warmer Mediterranean refugia. Our data also showed that within the Macaronesian Archipelagos, migrations occurred from Madeira towards the Azores, for both T. pavo and S. cretense, thus supporting a post-glacial colonization of the Azores by fish that persisted in the warmer region of Madeira. Similar geographic distributions, thermal affinities, and means of dispersion for T. pavo and S. cretense resulted in a similar response to the effects of Pleistocene glaciations, as evidenced by identical phylogeographic patterns.