Departamento de Xenética, Universidade de Santiago de Compostela, Facultade de Veterinaria, Campus de Lugo, 27002 Lugo, Spain.
Infect Genet Evol. 2011 Jul;11(5):904-11. doi: 10.1016/j.meegid.2011.02.015. Epub 2011 Mar 2.
Twelve microsatellite markers were used to characterize 130 clonal cultures of Perkinsus olseni derived from 30 clams from six different geographic locations. Only two loci were polymorphic in the four populations studied from Spanish coast (mean sample size = 31.2), and a third locus was variable in only two populations. In contrast, five parasites isolated from five clams from Japan and New Zealand showed variation at nine loci. Low genetic variation (2.08 ± 0.64 alleles per locus; mean genetic diversity: 0.101 ± 0.022), and very high F(IS) values (0.857 on average) were observed in Spanish populations. A total of 39 multilocus genotypes (MLGs) were identified in the whole sample (121 clonal isolates after excluding incomplete MLGs due to missing data). A three-level hierarchical analysis of molecular variance found significant levels of genetic variation within infrapopulations (all the parasites in a single host; Φ(IS) = 0.679) and among infrapopulations within the component population (all the parasites among a host population; Φ(SC) = 0.579). Differences among the component population from different geographic locations were not significant (Φ(CT) = 0.057). These results suggest that an important fraction of F(IS) is explained by the Wahlund effect, but also strong inbreeding within infrapopulations. Another explanation for the high F(IS) within infrapopulations is the presence of haploid and diploid stages in the clam. Although fully aquatic system provides many opportunities for mixing of parasites from different clams, results are consistent with the consideration of all P. olseni in a clam as a cohesive genetic unit (i.e., deme). If the parasite was introduced into the Spanish coast with the importation of infected clams from Asia and Oceania, the low microsatellite polymorphism could be reflecting founder effects in the recent evolutionary history of P. olseni. The loss of alleles would be intensified in a scenario structured in numerous demes because of recurrent founder effects at microgeographic level.
使用 12 个微卫星标记物对源自西班牙 6 个不同地理位置的 30 个蛤中的 130 个克隆培养物进行了特征描述。在所研究的来自西班牙海岸的 4 个种群中，仅有 2 个位点具有多态性（平均样本大小=31.2），而仅在两个种群中，第三个位点是可变的。相比之下，从日本和新西兰的 5 只蛤中分离出的 5 只寄生虫在 9 个位点上表现出变异。在西班牙种群中观察到遗传变异低（每个位点 2.08±0.64 个等位基因；平均遗传多样性：0.101±0.022），且非常高的 F（IS）值（平均 0.857）。在整个样本中总共鉴定出 39 个多位点基因型（MLG）（排除由于数据缺失而导致不完整的 MLG 后，共 121 个克隆分离株）。分子方差的三级分层分析发现，在亚种群内（单个宿主中的所有寄生虫；Φ（IS）=0.679）和亚种群内的种群内（宿主种群中的所有寄生虫；Φ（SC）=0.579）存在显著水平的遗传变异。来自不同地理位置的组成种群之间的差异不显著（Φ（CT）=0.057）。这些结果表明，F（IS）的一个重要部分是由Wahlund 效应解释的，但亚种群内的近亲繁殖也很强烈。亚种群内高 F（IS）的另一个解释是蛤中存在单倍体和二倍体阶段。尽管完全水生系统为来自不同蛤的寄生虫的混合提供了许多机会，但结果与将所有 P. olseni 视为蛤内有凝聚力的遗传单位（即种群）的考虑一致。如果寄生虫是随着来自亚洲和大洋洲的受感染蛤的进口而被引入西班牙海岸的，那么微卫星低多态性可能反映了 P. olseni 在最近的进化历史中的奠基者效应。在微地理水平上由于反复出现的奠基者效应，等位基因的丧失将在结构众多种群的情况下加剧。
