دانلود رایگان مقاله ترکیب گونه و تنوع ژنتیکی صدف پرورشی

Abstract

The common blue mussel (Mytilus edulis) was introduced to British Columbia, Canada, in the 1980s as an aquaculture alternative to native mussel species. Since then, the mussel industry in Pacific Canada has expanded and includes operations utilizing traditional methods of broodstock selection based on visual qualitative and quantitative traits. The impacts of hatchery propagation on genetic diversity and implications for animal fitness have been previously studied for other aquatic species, and this study further examines the effect of hatchery production on three M. edulis aquaculture populations in relation to a wild originator population. Prior to microsatellite genetic analysis, animals were identified to species using nuclear markers and were found to contain varying proportions of pure M. edulis as well as other pure species and hybrids from the ‘Mytilus edulis complex’. Subsequently seven microsatellite markers were used to genotype 166 pure adult M. edulis individuals, all of which exhibited high levels of polymorphism. Allele frequencies at multiple loci did not conform to Hardy–Weinberg expectations and substantially less genetic diversity and very low effective population size estimates (Ne, calculated from linkage disequilibrium) were observed in farmed populations compared to the wild reference population. All populations were found to be genetically distinct based on FST estimates. Mean allelic richness was approximately three times higher in the wild reference population than the three farmed populations (21 compared to 7.51, 7.91 in the two populations selecting for size and 8.24 in the population selecting for a colour morph). Observed heterozygosity was not significantly decreased in the cultured colour morph population, but was significantly different in the two other culture populations in comparison to the wild group. Reduced genetic diversity of the aquaculture populations is likely at least partially due to small effective breeding groups during hatchery propagation, creating genetic drift over successive generations. Speculations about the influence of broodstock selection practices are tentative and should be addressed in further temporal studies. These results indicate the need for the effective management of hatchery operations, the importance of rigorous site inventory, genetic broodstock characterization, and that ideally pedigree programs should be developed to help maintain healthy and productive shellfish culture populations with adaptive fitness capacity. Statement of relevance: Hatchery methods impact species purity and genetic diversity

4. Discussion

This study sought to examine the impact of hatchery propagation strategies on the genetic diversity of three aquaculture populations of marine mussels, in comparison to a wild reference population. We expected all sampled populations to contain either totally pure or very high proportions of pure Mytilus edulis; however, high proportions of M. edulis × M. galloprovincialis hybrids were discovered. There may be a number of factors influencing the species composition of these populations. Intuitively, it seems likely that the phenotypic similarity among species in the M. edulis complex may have resulted in other species being included as hatchery broodstock for subsequent juvenile production. Other potential factors include differential adaptation to hatchery conditions (FAO, 2008), varying survival of genotypes influenced by genotype-environment interactions (Slatkin, 1973; Springer and Heath, 2007) or the relatively high contribution to progeny of some contributors (Hedgecock, 1994; Lallias et al., 2010). Such effects would produce skewed broodstock species compositions and subsequent offspring, and be compounded over time with successive generations. That ISF produces a hybrid M. edulis: M. galloprovincialis line may have contributed to that farm having the highest level of cross-species hybridization in this study.