Abstract
Anchovies represent the largest world’s marine fish catches and the current threats on their populations impose a sustainable exploitment based on sound scientific information. In the European anchovy (Engraulis encrasicolus), the existence of several populations has been proposed but a global view is missing. Using a multidisciplinary approach, here we assessed the divergence among different ecotypes and its possible causes. SNPs have revealed two functionally distinct ecotypes overlapping in the Central Mediterranean, with one ecotype confined near the river estuaries. The same SNPs outliers also segregated two distinct populations in the near Atlantic, despite their large spatial distance. In addition, while most studies suggested that adaptation to low salinity is key to divergence, here we show that the offshore ecotype has higher environmental tolerance and an opportunistic feeding behaviour, as assessed by the study of environmental conditions, anchovy diet and trophic levels, and passive egg dispersal. These results provide insights into the anchovy evolutionary history, stressing the importance of behaviour in shaping ecotypes.
Highlights
The European anchovy (Engraulis encrasicolus) represents one of the most important European fishery resources[1]
The estuarine/lagunar populations that have been morphometrically and genetically identified in the Mediterranean Sea, Bay of Biscay and North Sea[3, 9, 11,12,13,14,15,16,17,18,19,20] could represent specific types of the coastal ecotype. These coastal populations are likely in the process of becoming reproductively isolated from other anchovy populations coexisting together in these basins17, 20, 21as result of parallel genetic differentiation prior to secondary contact[9, 17] and to local adaptation[19, 20]
According to assignment probabilities (AP) > 90%, we estimated the proportion of genotypes belonging to one of the two groups, in each sampling site (Fig. 1)
Summary
The European anchovy (Engraulis encrasicolus) represents one of the most important European fishery resources[1]. The current distribution of the marine ecotype is likely attributable to founding events into the Mediterranean Sea, Bay of Biscay and northern European seas by a common ancestral population that fled to the Mediterranean during last glaciation[6, 10]. The estuarine/lagunar populations that have been morphometrically and genetically identified in the Mediterranean Sea, Bay of Biscay and North Sea[3, 9, 11,12,13,14,15,16,17,18,19,20] could represent specific types of the coastal ecotype. The genetic relationship between the two ecotype pairs in Mediterranean and in the Atlantic Sea was analysed
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