日本鰻族群遺傳結構之長期變化

Abstract

族群遺傳分析常被應用於檢測分布廣泛的物種，藉以經營管理此物種的資源。在日本鰻，於過去研究利用微衛星DNA分析其族群遺傳結構之結果指出，其族群應為單一逢機交配，並無時間、空間上之分化。然而，日本鰻資源於1970年代開始產生顯著的下降，此現象是否會對其族群產生瓶頸效應、基因漂變以及近親交配之影響則尚無研究。在本研究中，我們利用7組多型性微衛星DNA，分析自1986年到2012年間於東亞緯度22°N 至 40°N十三個採集地取得之日本鰻鰻苗樣本，評估其基因多樣性。實驗結果發現，等位基因豐富度 (Allele richness = 14.78) 以及異型核子觀測值 (observed heterozygosity=0.68–0.85) 皆顯示日本鰻族群結構依舊維持高度基因多樣性，且近親交配程度低 (FIS= 0.066)。以時間尺度來看，各族群間並無顯著分化FST= 0.0069；近26年間有效族群數的估計依舊穩定維持，並無顯著改變 (有效族群數量範圍為24.7~無限大)。總結以上結果，日本鰻各年間族群結構依舊相當穩定，但之前可能發生過瓶頸效應。也就是說，就過去26年而言，日本鰻族群遺傳結構並未有明顯改變。

Population genetic analysis is commonly used to examine, manage, and conserve widespread species. The Japanese Eel (Anguilla japonica) is widely distributed in East Asia and its population size has dramatically declined since the 1970s. Recent studies using microsatellite loci indicate that panmixia was observed in A. japonica. There is no significant differentiation in the temporal or spatial scale of A. japonica, yet the historical demographics are not k now, such as whether the species suffered genetic bottlenecks, genetic drift, and/or inbreeding depression. We used 7 polymorphic microsatellite DNA loci from 13 geographic locations in East Asia, spanning from 22°N to 40°N, from 1985 to 2012 to understand the genetic diversity of A. japonica. Our data show that A. japonica still exhibits high genetic diversity in terms of average allelic richness (14.78) and observed heterozygosity (0.68–0.85). Inbreeding is rare (FIS= 0.066), and there is no genetic differentiation among annual cohorts (FST= 0.0069). The estimated mean effective population size (Ne) among the 26 years is modest (24.7 to infinity). In conclusion, there is no significant differentiation among annual groups of A. japonica. Simulation studies suggest that the population genetics of A. japonica has been stable for the past two decades, but might experience bottleneck in the past. No evidence of genetic bottleneck is found in the 26 annual cohorts. Accordingly, these data suggest that the population of A. japonica, under the current situation, does not face severe threat of losing genetic diversity.