Population genetics of the American eel (Anguilla rostrata): FST = 0 and NAO effects on demographic fluctuations of a panmictic species

We performed population genetic analyses on the American eel (Anguilla rostrata) with three main objectives. First, we conducted the most comprehensive analysis of neutral genetic population structure to date in order to revisit the null hypothesis of panmixia in this species. Second, we used this data to provide the first estimates of contemporary effective population size (Ne) and to document temporal variation in effective number of breeders (Nb) in American eel. Third, we tested for statistical associations between temporal variation in the North Atlantic Oscillation (NAO) index, the effective number of breeders and two indices of recruit abundance. A total of 2142 eels from 32 sampling locations were genotyped with 18 microsatellite loci. All measures of differentiation were essentially zero, and no evidence for significant spatial or temporal genetic differentiation was found. The panmixia hypothesis should thus be accepted for this species. Nb estimates varied by a factor of 23 among 12 cohorts, from 473 to 10 999. The effective population size Ne was estimated to be around 22 382. This study also showed that genetically based demographic indices, namely Nb and allelic richness (Ar), can be used as surrogates for the abundance of breeders and recruits, which were both shown to be positively influenced by variation during high (positive) NAO phases. Thus, long-term genetic monitoring of American glass eels at several sites along the North American Atlantic coast would represent a powerful and efficient complement to census monitoring to track demographic fluctuations and better understand their causes.

本研究针对美洲鳗鲡（Anguilla rostrata）开展群体遗传学分析，共设定三项核心研究目标。其一，开展截至目前最为全面的中性遗传群体结构分析，以重新验证该物种的泛交（panmixia）零假设；其二，利用本研究数据首次估算美洲鳗鲡的当代有效种群大小（Ne），并记录其有效繁殖个体数（Nb）的时间动态变化；其三，检验北大西洋涛动（NAO）指数的时间动态、有效繁殖个体数与2个补充群体丰度指数之间的统计学关联。本研究共对来自32个采样点的2142尾美洲鳗鲡进行了18个微卫星（microsatellite）位点的基因分型。所有遗传分化指标的测算值均接近于0，未发现显著的空间或时间尺度上的遗传分化证据，因此该物种的泛交零假设应予以支持。12个世代群的Nb估算值跨度达23倍，介于473至10999之间；有效种群大小Ne的估算值约为22382。本研究同时证实，基于遗传学的种群统计指标——即Nb与等位基因丰富度（Ar）——可作为繁殖个体与补充群体丰度的替代指标；研究发现二者均会受到北大西洋涛动高正值相位动态的正向影响。因此，在北美大西洋沿岸多个站点长期开展美洲玻璃鳗的遗传学监测，可作为种群普查监测的有力且高效补充手段，用于追踪种群动态波动并深入解析其成因。