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4.2. Genetic diversity: wild vs. cultured populationsResults indicated no significant loss of genetic diversity between wild and cultured populations of abalone based on estimates such as number of alleles, allelic richness or heterozygosity and in general were comparable amongst populations (Table S2, S3). This was in accord with previous findings for H. midae (Slabbert et al., 2009), es- timates for the Pacific abalone (H. discus hannai; An et al., 2011) and the blue abalone (H. fulgens; Gutierrez-Gonzalez and Perez- Enriguez, 2005) but contradicts findings for other studies on aqua- culture species including abalone (Alarcón et al., 2004; De la Cruz et al., 2010; Evans et al., 2004; Hara and Sekino, 2007; Li et al., 2007; Lind et al., 2009). A similar investigation, comparing F1-animals to wild populations, for H. midae by Evans et al. (2004) was based on a single spawning event, with a particular spawning cohort; thus the population sample, in that study, was not representative of the total production population. The reported loss of genetic diversity could, therefore be considered an artefact of a specific spawning event in an isolated breeding group: Differential parental contributions are well documented for broadcast spawning molluscs including South African abalone (Slabbert et al., 2009; Van den Berg and Roodt-Wilding, 2010). This may be for a number of reasons, including genetic fitness of particular individuals, but also stochastic variables, such as the condi- tion (e.g. physiological stress because of disease) of an individual animal at any given spawning event. Contrary to previous studies, the present investigation sampled individuals across spawning events and groups and therefore provides population-wide estimates that can account for the observed maintenance of genetic diversity. Furthermore, the high levels of genetic diversity in cultured populations may be attribut- ed to good management practice, by optimising the effective number of breeding individuals. It is noted that the cultured populations (in the present study) maintain comparatively large effective population sizes (57.9–185.1; combined LD estimate of Ne, Table 4). In comparison, esti- mates for, for example, cultured seabream (Sparus aurata; maximum Ne =18; Brown et al., 2005) and pearl oyster (Pinctada maxima; maxi- mum Ne = 9.2; Lind et al., 2009), reported losses in genetic diversity. This is noteworthy, especially considering that mass-spawning is the primary means of production in all the aforementioned species.The number of alleles observed per locus was significantly higher overall populations than within individual populations (Table S2, S3, S4) suggesting a number of population-specific alleles across these loci. Although this observation must be treated with caution due to the relatively small sample size used in the current study, a similar observation was made by An et al. (2011) for the Pacific abalone: This could be a result of founder effects that lead to a loss of rare al- leles in cultured populations (Skaala et al., 2004), noting that wild populations show the largest number of unique alleles, e.g. locus HmAD102T, HmRS27T and HmRS80T (Table S4). However, unique al- leles also persists in the cultured population, this can be explained by random genetic drift or, alternatively, by selection of differentially favoured alleles in diverse heterogeneous environments; this holds particular reference to locus HmidILL-140858T with unique alleles only in two cultured populations (CPSC and CPEC, Table S4) and evi- dence of differential selection between populations (Fig. 1).
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