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Fishery Bulletin 104(4) 



High rates of RAPD polymorphism 



Polymorphic rates of RAPD bands were much higher 

 between two populations of Epi?iephehis aivoara. The 

 number of reproducible and well-resolved bands analyzed 

 in the two populations ranged from 5 to 11. Monomor- 

 phic bands, constantly present in all individuals, varied 

 between primers, whereas total polymorphic bands were 

 observed 76.10% of the time for the two populations of 

 E. au'oara. The Xiamen population of £. aivoara exhib- 

 ited 66.66% polymorphism, whereas polymorphism was 

 46.54% in the Guangdong population (Table 1). RAPD 

 fragments of fewer than 1000 base pairs were found to 

 be more polymorphic than larger fragments. 



Genetic diversity 



Genetic diversity between populations was clearly illus- 

 trated in Table 2 and Table 3. The genetic diversity 

 statistics iHj, Hg, G^^, A^,„) estimated between the 

 two populations of Epinephelus awoara for each primer 

 are listed in Table 3. Nei's (1973) unbiased measures 

 of genetic identity and genetic distance between two 

 populations were 0.6216 and 0.4755, respectively. Within 

 the populations, total heterozygosity varied from 0.2189 

 to 0.4616 and expected heterozygosity ranged between 

 0.1232 and 0.2920. Probability (Fishers exact test) of 

 homogeneity was significant at P>0.05 for all primers 

 except S465, S513, S1026, S1044, and S1055. 



Discussion 



This study showed a considerable amount of genetic 

 variation present in Epinephehis aivoara. RAPD analysis 

 generated a large number of polymorphic DNA bands 

 (Table 1) between the populations of E. aivoara, thus 

 making it one of the most efficient systems for generat- 

 ing DNA markers. However, low levels of interspecific 

 variation were found in RAPD profiles among strains 

 of grouper. Therefore, it was an inefficient system for 

 generating molecular markers for gene mapping (Liu 

 et al., 1999). 



Several authors (Welsh and McClelland, 1990; Bar- 

 dakci and Skibinski, 1994; Naish et al., 1995) have 

 demonstrated that the RAPD PCR method is a power- 

 ful tool for the assessment of genetic markers that are 

 capable of discriminating between species or subspecies 

 in a wide range of organisms, including fishes. This ca- 

 pacity was confirmed by the results of the present study 

 because, for all screened primers, different RAPD band- 

 ing patterns were observed between the two populations 

 (Table 1). A limitation arising with the application of 

 the RAPD technique is the homology between comigrat- 

 ing bands produced by the same primer in different 

 individuals (Hadrys et al., 1992). Nevertheless, in the 

 present study, homology constitutes a valid assumption 

 because all individuals belong to the same species. 



Despite the fact that no specific markers were found 

 to identify Epinephelus awoara species, data analysis of 



the observed and effective number of alleles revealed a 

 degree of divergence (Table 2). The Nei (1973) gene di- 

 versity was also illustrated in Table 2. The two popula- 

 tions of E. aivoara (Table 3) showed high level of genetic 

 variation (i.e.. Shannon's information index; Shannon- 

 Weaver, 1949, average genetic index [Hp,,!,] and genetic 

 diversity index between populations [H^p]). Similarly 

 a high level of genetic variation and genetic distance 

 (0.617-0.949) was observed in dinoflagellates (Baillie et 

 al., 2000). This finding supports a high genetic distance 

 for E. awoara (0.4755) in the present study. This may 

 be due to the selection pressure of pollutants (Nadig 

 et al., 1998) or to overexploitation of groupers in the 

 South China Sea. 



Total heterozygosity (Hy.) values ranged from 0.2189 

 to 0.4616, expected heterozygosity (Hg) from 0.1232 to 

 0.3157, and an estimate of gene flow (iV„,) from 0.3714 to 

 4.1722. The proportion of total genetic variation within 

 species due to population differentiation (G^.-,) ranged 

 from 0.1070 to 0.5344 (Table 3). Carvalho et al. (1991) 

 observed a very high differentiation (Gc;y,= 0.648) in 

 the guppy (Poecilia reticulata) in northern Trinidad. 

 Similarly, Ward et al. (1994) also observed high G^j 

 values (>0.2000). In any case, the divergence in G^j 

 values indicates that, on average, marine subpopula- 

 tions exchange between one and two orders of magni- 

 tude more migrants per generation. Genetic divergence 

 between areas originates when populations are formed 

 or through the restriction of gene flow (Lage et al., 

 2004). Higher H^ in marine fish is at least consistent 

 with these fish having, on average, larger population 

 sizes. Homogeneity of gene frequencies was found to be 

 significant (P>0.05) across populations of Epinephelus 

 awoara (Fig. 1) for most of the primers except S465, 

 S513, S1026, S1044,and S1055 (P>0.001). 



The factor that could influence the genetic variation of 

 the grouper population geographically is the movement 

 of adults, which can be extensive and cover considerable 

 distances (Harding et al., 1997). The otherwise shelter- 

 habituated adults travel long distances necessary to 

 populate remote oceanic islands. The Bermuda fauna 

 include more than 75% of the known west Indian grou- 

 pers even though Bermuda lies more than 800 miles 

 from other coral reefs. Such distributional patterns 

 are best explained as the result of passive transport of 

 larvae by oceanic currents. Similar patterns are also 

 expected in the South China Sea. Adult movement of 

 marine fish is relatively unfettered by physical barri- 

 ers. In addition to gene flow through adult migration, 

 marine fish frequently have a planktonic larval stage 

 of several months duration, which can be expected to 

 further enhance gene flow. 



Estimation of genetic diversity of Epinephelus awoara 

 by RAPD analysis (i.e., by using the mean of observed 

 number of alleles [Na]. effective number of alleles [Ne] 

 and Nei's gene diversity [//]) was found to be 1.6563, 

 1.4169, and 0.2915, respectively for Xiamen popula- 

 tions, whereas they were 1.4824, 1.2713, 0.2167, respec- 

 tively for Guangdong populations. Our results provide 

 evidence for a loss (10.5%, 11.3%, and 25.7%, respec- 



