日本鰻族群遺傳結構之時空分析

Abstract

日本鰻(Anguilla japonica)的資源量在1970年後即急速下降，毫無疑問的對該物種進行保育和資源管理有急切的需要，然而日本鰻的族群遺傳結構不論由時間或空間上進行探討，到目前為止仍然沒有定論。本研究使用八組具有多型性的微衛星DNA基因座，由時間和空間尺度觀察日本鰻之遺傳組成，分析北台灣淡水河河口連續由1986到2007年年間採集的鰻線樣本，年內的鰻線樣本則逐月採集於2001年11月至2002年4月台灣福隆河口以及2002年2月至同年4月日本Mikawa Bay地區的鰻線，不同地理空間的鰻線樣本則分別於台灣、中國大陸、韓國、日本進行採集。結果顯示不論由時間或空間尺度觀察，其遺傳分化指數都非常低，在總體不同年間和空間的來游群間存有顯著差異，不同時間的來游群之間遺傳變異程度高於不同地理空間來游群之間的遺傳變異。然而在遺傳分化兩兩比對、多元尺度分析 (MDS)、遺傳演化樹分析都顯示，所有來游群間不論在時間或空間上皆屬同一族群，且因為地理距離和因時間差異所產生的遺傳隔離測試也顯示，不論在空間和時間上皆無顯著之遺傳結構存在。在本研究中來游群間隨機偶發性的遺傳變異並不能產生穩定持久的遺傳結構。本結果強力的支持東亞的日本鰻是屬於一個逢機交配族群，因此在保育議題上應把日本鰻視為一個單一的管理單位。

The Japanese eel Anguilla japonica has dramatically declined in East Asia since the 1970s. Consequently, conservation and resource management of this species is urgently required. However, the population genetic structure of the Japanese eel, in temporal and spatial scales, is still poorly understood. We used 8 polymorphic microsatellite DNA loci to investigate the genetic composition of the Japanese eel. Inter-annual glass eel specimens were collected yearly between 1986 and 2007 from the Danshui River estuary, northern Taiwan. Intra-annual glass eel specimens were collected monthly from the Fulong estuary, Taiwan, between November 2001 and April 2002 and from Mikawa Bay, Japan, between February and April 2002. Spatial glass eel specimens were collected from Taiwan, China, Korea, and Japan. Overall genetic differentiation among the intra-annual, inter-annual, or spatial recruits was very low, and significance was observed among inter-annual and spatial recruits. Genetic variation among temporal components exceeded that among geographical components. However, pairwise genetic comparisons, multidimensional scaling (MDS), and the phylogenetic tree of all recruits showed no evidence of genetic differentiation in temporal or spatial scales. The isolation by distance (IBD) and isolation by time (IBT) tests showed no evidence of genetic structuring in the spatial and temporal scales, respectively. Occasional genetic variations among recruits occurred on a random scale, and this could not create a stable lasting genetic structure. The results strongly support the presence of a panmictic population of the Japanese eel in East Asia. Therefore, the Japanese eel should be considered as only a single management unit in conservation issues.