STUDY OF GENETIC GRADIENTS AMONG POPULATIONS OF ATLANTIC ANCHOVY ENGRAULIS ENCRASICOLUS L. LOCATED ALONG MARINE ECOTONES

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Study of genetic gradients among populations of Atlantic anchovy (Engraulis encrasicolus L.) located along marine ecotones

Publication . Silva, Gonçalo Jorge Franco; Castilho, Rita

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.

2014Doctoral thesis

Open Access

Wandering behaviour prevents inter and intra oceanic speciation in a coastal pelagic fish

Publication . Silva, Goncalo; Cunha, Regina L.; Ramos, Ana; Castilho, Rita

Small pelagic fishes have the ability to disperse over long distances and may present complex evolutionary histories. Here, Old World Anchovies (OWA) were used as a model system to understand genetic patterns and connectivity of fish between the Atlantic and Pacific basins. We surveyed 16 locations worldwide using mtDNA and 8 microsatellite loci for genetic parameters, and mtDNA (cyt b; 16S) and nuclear (RAG1; RAG2) regions for dating major lineage-splitting events within Engraulidae family. The OWA genetic divergences (0-0.4%) are compatible with intra-specific divergence, showing evidence of both ancient and contemporary admixture between the Pacific and Atlantic populations, enhanced by high asymmetrical migration from the Pacific to the Atlantic. The estimated divergence between Atlantic and Pacific anchovies (0.67 [0.53-0.80] Ma) matches a severe drop of sea temperature during the Gunz glacial stage of the Pleistocene. Our results support an alternative evolutionary scenario for the OWA, suggesting a coastal migration along south Asia, Middle East and eastern Africa continental platforms, followed by the colonization of the Atlantic via the Cape of the Good Hope.

2017-06Journal article

Open Access

Thermal adaptation and clinal mitochondrial DNA variation of European anchovy

Publication . Silva, Goncalo; Lima, Fernando P.; Martel, Paulo; Castilho, Rita

Natural populations of widely distributed organisms often exhibit genetic clinal variation over their geographical ranges. The European anchovy, Engraulis encrasicolus, illustrates this by displaying a two-clade mitochondrial structure clinally arranged along the eastern Atlantic. One clade has low frequencies at higher latitudes, whereas the other has an anti-tropical distribution, with frequencies decreasing towards the tropics. The distribution pattern of these clades has been explained as a consequence of secondary contact after an ancient geographical isolation. However, it is not unlikely that selection acts on mitochondria whose genes are involved in relevant oxidative phosphorylation processes. In this study, we performed selection tests on a fragment of 1044 bp of the mitochondrial cytochrome b gene using 455 individuals from 18 locations. We also tested correlations of six environmental features: temperature, salinity, apparent oxygen utilization and nutrient concentrations of phosphate, nitrate and silicate, on a compilation of mitochondrial clade frequencies from 66 sampling sites comprising 2776 specimens from previously published studies. Positive selection in a single codon was detected predominantly (99%) in the anti-tropical clade and temperature was the most relevant environmental predictor, contributing with 59% of the variance in the geographical distribution of clade frequencies. These findings strongly suggest that temperature is shaping the contemporary distribution of mitochondrial DNA clade frequencies in the European anchovy.

2014-10Journal article

Open Access