Abstract
Small giant clam, Tridacna maxima, widely distributed from French Polynesia to East Africa, has faced population declines due to over-exploitation. Comoros islands are an important biogeographic region due to potential richness of marine species, but no relevant information is available. In order to facilitate devising effective conservation management plan for T. maxima, nine microsatellite markers were used to survey genetic diversity and population differentiation of 72 specimens collected from three Comoros islands, Grande Comore, Moheli and Anjouan. A total of 51 alleles were detected ranged from 2 to 8 per locus. Observed and expected heterozygosity varied from 0.260 to 0.790 and from 0.542 to 0.830, respectively. All populations have high genetic diversity, especially the population in Moheli, a protected area, has higher genetic diversity than the others. Significant heterozygote deficiencies were recorded, and null alleles were probably the main factor leading to these deficits. F ST value indicated medium genetic differentiation among the populations. Although significant, AMOVA revealed 48.9 % of genetic variation within individuals and only a small variation of 8.9 % was found between populations. Gene flow was high (Nm = 12.40) between Grande Comore and Moheli, while lower (Nm = 1.80) between Grande Comore and Anjouan, explaining geographic barriers to genetic exchanges might exist in these two islands. Global gene flow analysis (Nm = 5.50) showed that larval dispersal is enough to move between the islands. The high genetic diversity and medium population differentiation revealed in the present study offer useful information on genetic conservation of small giant clams.
Highlights
The giant clam subfamily Tridacninae (Schneider and Foighil 1999) is the most widespread of the bivalves and is distributed throughout the Red sea and Indo-Pacific Ocean, from French Polynesia to East Africa
Genetic diversity and deviation from Hardy–Weinberg equilibrium (HWE) Previous studies have indicated a high level of genetic diversity on T. maxima in Indo-Pacific Ocean
2009) and other species on Tridacnidae family (Kochzius and Nuryanto 2008; DeBoer and Barber 2010; Hui et al 2011). This present study shows a high level of genetic diversity for the small giant clams (HE = 0.699–0.714) within populations
Summary
The giant clam subfamily Tridacninae (Schneider and Foighil 1999) is the most widespread of the bivalves and is distributed throughout the Red sea and Indo-Pacific Ocean, from French Polynesia to East Africa (bin Othman et al 2010). T. noae was separated from T. maxima by their genetic and morphological description (Su et al 2014) Among these bivalves, T. maxima has commonly the largest distribution range (Lucas 1988). Small giant clam species (T. maxima) are sedentary as adults, reproduce by broadcast spawning with high fecundity (>106 eggs per female), and have pelagic larval dispersal about 9 days (Lucas 1988). Based on these aspects, population genetics studies can provide more information about the ecological interactions, larval dispersal, distribution patterns, as well as evolution of the species. Genetic variations studies using allozyme analysis (Campbell et al 1975; Laurent et al 2002) and, recently, mitochondrial markers (Nuryanto and Kochzius 2009), have provided information on highly genetic variability, larval dispersal and the connectivity of different sites of Indo-Pacific Ocean that can be explained by marine currents or geographic isolation (Benzie and Williams 1992a, b)
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