Abstract
The southern hemisphere sardine Sardinops sagax is common in two of South Africa’s temperature-defined marine provinces (cool-temperate West Coast and warm-temperate South Coast), and during the KwaZulu-Natal sardine run, it is also represented on the subtropical East Coast. Non-genetic data suggest that the species may comprise at least two regional stocks that need to be managed separately, and it is possible that different environmental conditions among the provinces may have influenced population structure and driven adaptive divergence. However, genetic evidence for such spatial heterogeneity is lacking, and results from previous studies using traditional molecular methods remain inconclusive. As a result, a single-stock management strategy is presently being applied, which can potentially result in stock collapses as regional stocks become overexploited. To address this question, genome-wide DNA data were generated to determine whether there is evidence for genetic differentiation between sardines from the different bioregions. As a means of assessing the role of active adult dispersal in the sardines in reducing genetic differentiation between regions, genomic data were also generated from an endemic goby whose range is almost identical, but whose adults are sedentary. The majority of genomic markers were selectively neutral, and a pattern of isolation by geographic distance was found in both species. However, genetic clusters did not clearly match pre-defined marine bioregions. In contrast, outlier loci under thermal selection identified regional genetic clusters that could be linked to bioregions in both species, with stronger...
Ph.D. (Zoology)