Translocation of wild populations: conservation implications for the genetic diversity of the black-lipped pearl oyster Pinctada margaritifera

Translocation has been widely studied as a tool for conservation management to restore or enhance degraded populations. On the contrary few studies have been conducted on translocation for commercial purposes. In this study we evaluate the genetic consequences of translocation of wild individuals of Pinctada margaritifera on farmed and adjacent wild populations. We tested the hypotheses that translocations would induce high genetic heterogeneity in farmed populations and this heterogeneity would then leak into the adjacent wild populations. In fact, farmed samples exhibit high levels of heterogeneity and low pairwise relatedness compared to wild populations, highlighting the pooling of genetically divergent populations into farms. We also demonstrate that this heterogeneity is transmitted to adjacent wild populations as a result of interbreeding. Adjacent wild populations tend to have higher genetic diversity values and greater pairwise relatedness coefficient with farmed populations than wild populations. Overall pearl culture in French Polynesia promotes the mixing of unrelated individuals in farmed locations and reduces genetic divergence among geographically distant populations as well as among farmed and wild populations of a same lagoon. We also studied for the first time, a farmed population originating from spat collected in a lagoon where release of hatchery produced larvae occurred ten year ago and we were able to identify four distinct genetic groups. These groups contribute highly to reproduction and caused considerable genetic drift in the lagoon, suggesting that hatchery produced larvae are neither sustainable method for pearl culture nor for conserving the diversity of P. margaritifera in French Polynesia.

移殖（translocation）作为保护管理手段以修复或增强退化种群的研究已被广泛开展，但针对商业目的的移殖研究却寥寥无几。本研究针对黑蝶珍珠贝（Pinctada margaritifera）野生个体的移殖行为，评估其对养殖种群及邻近野生种群的遗传影响。我们提出并验证了如下假说：移殖会使养殖种群产生较高的遗传异质性，且该异质性会扩散至邻近的野生种群。研究结果显示，相较于野生种群，养殖样本的遗传异质性水平更高，个体间的成对亲缘关系则更低，这表明养殖场内汇集了遗传背景差异显著的种群。本研究同时证实，由于养殖与野生个体间的杂交，该遗传异质性会传递至邻近的野生种群。与远离养殖区的野生种群相比，邻近养殖区的野生种群往往具有更高的遗传多样性，且与养殖种群的成对亲缘系数也更高。总体而言，法属波利尼西亚的珍珠养殖产业推动了养殖区域内无关个体的混合，并降低了地理间隔较远种群间的遗传分化，同时也缩小了同一泻湖内养殖种群与野生种群间的遗传差异。本研究还首次对一个养殖种群展开分析：该种群的幼贝采自十年前曾投放过人工孵化幼体的泻湖，研究人员成功鉴定出四个独立的遗传类群。这些遗传类群对泻湖内的繁殖贡献显著，并引发了显著的遗传漂变，这表明人工孵化幼体既无法作为珍珠养殖的可持续手段，也无法有效保护法属波利尼西亚境内黑蝶珍珠贝的种群多样性。