Genetic association analysis of candidate loci under selection with size in the South African abalone

The abalone, Haliotis midae, is an important aquaculture species in South Africa and the largest generator of revenue for the mariculture sector. Despite domestication of this species still being in the initial stages, significant differentiation has been observed between wild and cultured populations. The genetic consequences of founder effects have been well documented in many aquaculture species; however, the effects of selection remain under-investigated. Previous studies in this species identified several loci thought to be under divergent selection between wild and cultured populations. The aim of this study was therefore to investigate the influence of artificial selection on genetic variation by determining whether these candidate loci are associated with larger size (primary production trait) in a commercial F₁ population. Thirteen microsatellite markers, putatively identified as being under directional selection, were chosen for association analysis. Various statistical tests were used to detect significant genotype-phenotype associations within a family-bias corrected population cohort and two family cohorts. Two loci demonstrated significant evidence for association with size, with both loci possessing alleles that correlated significantly with either increased or decreased size. As size is currently the only trait actively selected for in terms of production, the current results suggest that natural selection for adaptation to the novel aquaculture environment is the predominant selective force shaping genetic variation during the initial stages of domestication in abalone. Furthermore, whilst it is currently unclear as to whether these loci represent causative variants for size traits, they may be useful in future molecular-assisted breeding programmes for H. midae.