Department of Biology, University of Eastern Finland, Joensuu, Finland.
BMC Ecol. 2014 Jul 9;14:22. doi: 10.1186/1472-6785-14-22.
Small, genetically uniform populations may face an elevated risk of extinction due to reduced environmental adaptability and individual fitness. Fragmentation can intensify these genetic adversities and, therefore, dispersal and gene flow among subpopulations within an isolated population is often essential for maintaining its viability. Using microsatellite and mtDNA data, we examined genetic diversity, spatial differentiation, interregional gene flow, and effective population sizes in the critically endangered Saimaa ringed seal (Phoca hispida saimensis), which is endemic to the large but highly fragmented Lake Saimaa in southeastern Finland.
Microsatellite diversity within the subspecies (HE = 0.36) ranks among the lowest thus far recorded within the order Pinnipedia, with signs of ongoing loss of individual heterozygosity, reflecting very low effective subpopulation sizes. Bayesian assignment analyses of the microsatellite data revealed clear genetic differentiation among the main breeding areas, but interregional structuring was substantially weaker in biparentally inherited microsatellites (FST = 0.107) than in maternally inherited mtDNA (FST = 0.444), indicating a sevenfold difference in the gene flow mediated by males versus females.
Genetic structuring in the population appears to arise from the joint effects of multiple factors, including small effective subpopulation sizes, a fragmented lacustrine habitat, and behavioural dispersal limitation. The fine-scale differentiation found in the landlocked Saimaa ringed seal is especially surprising when contrasted with marine ringed seals, which often exhibit near-panmixia among subpopulations separated by hundreds or even thousands of kilometres. Our results demonstrate that population structures of endangered animals cannot be predicted based on data on even closely related species or subspecies.
由于环境适应能力和个体适应性降低，遗传上均匀的小种群可能面临更高的灭绝风险。片段化会加剧这些遗传逆境，因此，分散和基因流在孤立种群内的亚种群之间对于维持其生存能力通常是必不可少的。利用微卫星和 mtDNA 数据，我们研究了极度濒危的塞马环斑海豹（Phoca hispida saimensis）的遗传多样性、空间分化、区域间基因流动和有效种群大小，该物种仅存在于芬兰东南部大而高度片段化的塞马湖。
该亚种内的微卫星多样性（HE=0.36）是鳍足类动物中迄今为止记录的最低水平之一，存在个体杂合性持续丧失的迹象，反映出非常低的有效亚种群大小。微卫星数据分析的贝叶斯分配结果显示，主要繁殖区之间存在明显的遗传分化，但在双亲遗传的微卫星（FST=0.107）中，区域间结构明显弱于母系遗传的 mtDNA（FST=0.444），表明雌雄两性介导的基因流动存在七倍差异。
种群中的遗传结构似乎是由多种因素的共同作用产生的，包括有效亚种群规模小、湖泊栖息地片段化以及行为扩散限制。在内陆塞马环斑海豹中发现的精细分化尤其令人惊讶，因为与海洋环斑海豹相比，后者通常在数百甚至数千公里分隔的亚种群之间表现出近乎混合的现象。我们的研究结果表明，即使是基于密切相关的物种或亚种的数据，也无法预测濒危动物的种群结构。
