Molecular analysis of genetic variation and relationships within the population of abalone (Haliotis midae) at the Sea Plant Products abalone hatchery, Hermanus, R.S.A.

[摘要] ENGLISH ABSTRACT:The species Haliotis midae is the only commercially exploitable abalonespecies of the six found in the South African coastal waters. This species isunder substantial pressure from both legal and illegal harvesters, to such anextent that it could be commercially extinct within four years. Efforts toalleviate the pressures on the natural populations of both illegal and legalharvesting are being made. The genetic management systems for abalonefarming and ranching activities should be carefully evaluated. The loss ofgenetic diversity and the risks of contaminating the gene pools of naturalpopulations in the vicinity of a farm should be minimized. Genetic evaluationstudies will be at great importance to acquire the necessary data needed forgenetic diversity and differentiation analysis.The aim at this study was to develop species-specific microsatellite DNAmarkers to assess the genetic diversity and differentiation within and betweenthe brood stock and commercial stock of the Sea Plant Products abalone farm(Hermanus, Republic of South Africa) and natural populations related to thebrood stock. The species-specific DNA markers were also used for parentageassignments within the tarm population (first for abalone) and preliminary OTL(quantitative trait loci)-discovery analysis studying growth rate segregation.Samples were taken of the farm's brood stock and commercial stock (Rows 2,3, 4) as well as from two natural populations (Saldanha Bay and Black Rock)related to the brood stock. Various statistical parameters and softwarepackages were used to assess genetic diversity and differentiation, to inferparentage and to look for OTL's.Eight species-specific microsatellite DNA markers were designed and usedfor data analysis. Data analysis showed a loss at genetic diversity from thebrood stock to the commercial stock caused by the subdivision of the originalbrood stock into rows and the differential contributions of parents to theoffspring. No genetic differentiation (Fst) was detected between the farm andnatural populations, except for the offspring of Row2. levels of inbreeding(ns) were high for all loci within the populations. Thirty-eight percent of allstudied offspring were confidently assigned to a couple. The preliminary QTldiscoverysuggested the segregation of a number of alleles and genotypeswith growth rate.The study concluded that the commercial abalone population of the Sea PlantProducts abalone farm holds no threat to the disruption of the genetic diversityof the natural populations. It is proposed that the farm implement a rotationalbreeding program to increase the genetic diversity of the commercialpopulation. Any newly acquired brood stock must be profiled before theirintroduction into the breeding program to assess the influence of the animalson the current levels of genetic diversity within the farm. The accuracy andreliability of parentage assignments and QTl-discovery need to be optimisedby adding more loci and sampling more animals or even by trying anddeveloping new methods.

[发布机构] Stellenbosch University