Low genetic variability in a widely distributed and abundant clupeid species, Sardinella aurita. New empirical results and interpretations

Considering the wide geographic distribution and the catches of Sardinella aurita, the observed allozyme diversity (H=0.011) is strikingly small. Potential explanations for this low gene diversity, which include restrictions on effective population size owing to variance in reproductive success, demographic instability, historical bottlenecks in population size, selection, and technical artifacts are examined and quantified. This quantification, though rough, shows that no single Factor can account for the lack of diversity. However, demographic instability of S, aurita, especially if this instability has persisted over evolutionary time scales, together with much greater than Poisson variance in individual reproductive success, could account reasonably for the results. Pleistocene reduction of population size seems also a necessary co-factor. Technical artifacts, mostly scoring difficulties linked to liver autolysis, are considered also and analysed in different clupeid species. (C) 1998 The Fisheries Society of the British Isles.