Browsing by Author "Stefanni, S."
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- Ancient divergence in the trans-oceanic deep-sea shark Centroscymnus crepidaterPublication . Cunha, R. L.; Coscia, I.; Madeira, C.; Mariani, S.; Stefanni, S.; Castilho, RitaUnravelling the genetic structure and phylogeographic patterns of deep-sea sharks is particularly challenging given the inherent difficulty in obtaining samples. The deep-sea shark Centroscymnus crepidater is a medium-sized benthopelagic species that exhibits a circumglobal distribution occurring both in the Atlantic and Indo-Pacific Oceans. Contrary to the wealth of phylogeographic studies focused on coastal sharks, the genetic structure of bathyal species remains largely unexplored. We used a fragment of the mitochondrial DNA control region, and microsatellite data, to examine genetic structure in C. crepidater collected from the Atlantic Ocean, Tasman Sea, and southern Pacific Ocean (Chatham Rise). Two deeply divergent (3.1%) mtDNA clades were recovered, with one clade including both Atlantic and Pacific specimens, and the other composed of Atlantic samples with a single specimen from the Pacific (Chatham Rise). Bayesian analyses estimated this splitting in the Miocene at about 15 million years ago. The ancestral C. crepidater lineage was probably widely distributed in the Atlantic and Indo-Pacific Oceans. The oceanic cooling observed during the Miocene due to an Antarctic glaciation and the Tethys closure caused changes in environmental conditions that presumably restricted gene flow between basins. Fluctuations in food resources in the Southern Ocean might have promoted the dispersal of C. crepidater throughout the northern Atlantic where habitat conditions were more suitable during the Miocene. The significant genetic structure revealed by microsatellite data suggests the existence of present-day barriers to gene flow between the Atlantic and Pacific populations most likely due to the influence of the Agulhas Current retroflection on prey movements.
- Establishment of a coastal fish in the Azores: recent colonisation or sudden expansion of an ancient relict population?Publication . Stefanni, S.; Castilho, Rita; Sala-Bozano, M.; Robalo, J. I.; Francisco, S. M.; Santos, R. S.; Marques, N.; Brito, A.; Almada, V. C.; Mariani, S.The processes and timescales associated with ocean-wide changes in the distribution of marine species have intrigued biologists since Darwin's earliest insights into biogeography. The Azores, a mid-Atlantic volcanic archipelago located >1000 km off the European continental shelf, offers ideal opportunities to investigate phylogeographic colonisation scenarios. The benthopelagic sparid fish known as the common two-banded seabream (Diplodus vulgaris) is now relatively common along the coastline of the Azores archipelago, but was virtually absent before the 1990s. We employed a multiple genetic marker approach to test whether the successful establishment of the Azorean population derives from a recent colonisation from western continental/island populations or from the demographic explosion of an ancient relict population. Results from nuclear and mtDNA sequences show that all Atlantic and Mediterranean populations belong to the same phylogroup, though microsatellite data indicate significant genetic divergence between the Azorean sample and all other locations, as well as among Macaronesian, western Iberian and Mediterranean regions. The results from Approximate Bayesian Computation indicate that D. vulgaris has likely inhabited the Azores for similar to 40 (95% confidence interval (CI): 5.5-83.6) to 52 (95% CI: 6.32-89.0) generations, corresponding to roughly 80-150 years, suggesting near-contemporary colonisation, followed by a more recent demographic expansion that could have been facilitated by changing climate conditions. Moreover, the lack of previous records of this species over the past century, together with the absence of lineage separation and the presence of relatively few private alleles, do not exclude the possibility of an even more recent colonisation event.
- Molecular insights indicate that Pachycara thermophilum (Geistdoerfer, 1994) and P. saldanhai (Biscoito and Almeida, 2004) (Perciformes: Zoarcidae) from the Mid-Atlantic Ridge are synonyms speciesPublication . Stefanni, S.; Porteiro, F. M.; Bettencourt, R.; Gavaia, Paulo J.; Santos, Ricardo SerrãoThe genus Pachycara comprises of 20 species distributed across the globe. Due to difficulties in collecting these fish, most of the species were described from single or few individuals. Until now, the systematics for these species has been based on traditional taxonomy and the only studies with molecular interest were performed on the Circum Antarctic Pachycara brachycephalum.
- Phylogenetic relationships of the North-eastern Atlantic and Mediterranean forms of Atherina (Pisces, Atherinidae)Publication . Francisco, S. M.; Congiu, L.; Stefanni, S.; Castilho, Rita; Brito, A. B.; Ivanova, P. P.; Levy, A.; Cabral, H.; Kilias, G.; Doadrio, I.; Almada, V. C.The genus Atherina (Sand-smelts) is distributed in the Eastern Atlantic Ocean and Mediterranean Sea, extending south along the African coast into the Indian Ocean (Quignard and Pras, 1986). It is a genus of small inshore fishes with many populations living in brackish and freshwater. The taxonomy of the genus has been troublesome due to the intraspecific variability of some of its species, the overlap of characters among many of them and because many nominal species were apparently described based on individuals originating from different localities.