Within-population structure highlighted by differential introgression across semipermeable barriers to gene flow in Anguilla marmorata

In the marine environment, differential gene exchange between partially reproductively isolated taxa can result in introgression that extends over long distances due to high larval dispersal potential. However, the degree to which this process contributes to inter-locus variance of genetic differentiation within introgressed populations remains unclear. Using a genome-scan approach in the Indo-Pacific eel Anguilla marmorata, we investigated the degree of interpopulation genetic differentiation, the rate of introgression, and within-population genetic patterns at 858 AFLP markers genotyped in 1117 individuals. Three divergent populations were identified based on clustering analysis. Genetic assignments of individuals revealed the existence of different types of hybrids that tended to co-occur with parental genotypes in three population contact zones. Highly variable levels of genetic differentiation were found between populations across the AFLP markers, and reduced rates of introgression were shown at some highly differentiated loci. Gene flow across semipermeable genetic barriers was shown to generate spatial introgression patterns at some loci which define within-population structure over long distances. These results suggest that differential introgression in subdivided populations may be relevant when interpreting spatial variation patterns displayed by outlying loci in other marine fish populations.

在海洋环境中，部分生殖隔离类群间的差异基因交流可借助幼虫的高扩散潜力，产生可长距离扩散的渐渗（introgression）现象。然而，该过程对渐渗种群内遗传分化的位点间方差的贡献程度仍未明确。
本研究以印度-太平洋鳗——花鳗鲡（Anguilla marmorata）为研究对象，采用基因组扫描（genome-scan）方法，对1117个个体的858个扩增片段长度多态性（AFLP, Amplified Fragment Length Polymorphism）标记进行基因分型，以此分析种群间遗传分化程度、渐渗速率以及种群内遗传模式。
经聚类分析，本研究共鉴定出3个遗传分化显著的种群。个体遗传归属分析结果显示，存在多种杂交个体类型，且这些杂交个体多与亲本基因型在3个种群接触带中共存。
研究发现，不同种群间的AFLP标记遗传分化水平存在显著差异，且部分高度分化的位点表现出较低的渐渗速率。跨越半透性遗传屏障的基因流可在部分位点形成空间渐渗模式，进而在长距离尺度上塑造种群内遗传结构。
上述结果表明，在解释其他海洋鱼类种群中异常位点所呈现的空间变异模式时，局部分化种群间的差异渐渗效应可能具有重要参考价值。