| Summary: | The Quaternary climate oscillations had a major role in shaping the genetic architecture of living species. In the marine realm, the apparent lack of physical barriers to dispersal allows organisms to track optimum physiological conditions by displacing their distribution ranges. The European anchovy Engraulis encrasicolus is a small pelagic fish that has a broad distribution range in the Atlantic Ocean. Despite the high ability for dispersal, this species exhibit an unusual population structure and two mitochondrial clades clinally distributed along the eastern Atlantic and the Mediterranean. In the present thesis, we investigated North Atlantic anchovy’s response to climate cycles at the leading edges of the distribution range. These small pelagic fishes massively followed suitable thermal conditions cyclically over the Pleistocene and therefore were able to preserve high levels of genetic diversity. We further explored the variation of the mitochondrial clades of the European anchovy and found that the anti-tropically distributed clade is under positive selection, suggesting that temperature is shaping the contemporary distribution of mtDNA clade frequencies. The Old World Anchovies (OWA) complex, of which the European anchovy is part, has taxa distributed in the Pacific and Atlantic oceans. This complex originated at 3.16 Ma in the Indo-Pacific during the late Pliocene and split in two groups, one that remained in the Pacific Ocean and one that colonized the Atlantic Ocean during the Pleistocene (0.62 Ma). The genetic patterns among the OWA indicate no genetic diferentiation between putative species from the Atlantic Ocean, and low levels of ongoing geneflow between Atlantic and Pacific anchovies. Within the Pacific Ocean, two well supported mitochondrial clades reveal ancient trans- Equatorial migrations, while nuclear loci support contemporary admixture. As oscilações climáticas do Quaternário tiveram um papel fundamental na modelação da arquitectura genética das espécies vivas. No meio marinho a ...
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