東亞島弧海域小鰭鰭尾鯙初期生活史與族群遺傳結構之探討

Abstract

幼生漂浮期 (Pelagic larval duration, PLD) 的擴散與補充，可能對於底棲性魚類成體的分布範圍及族群結構有重要影響。本研究對象小鰭鰭尾鯙 (Uropterygius micropterus) 具有廣分布、在地產卵、成熟體型小、移動能力低及棲位寬度狹窄等特性，值得從幼生漂浮期與族群遺傳結構探究上述物種特性。小鰭鰭尾鯙採自三個國家八個樣點共176尾：(1) 日本石垣島 (Ishigaki)；(2) 臺灣大溪、石梯坪、基翬、黃金海岸、萬里桐及小琉球；(3) 菲律賓巴迪安 (Badian)。以粒線體DNA之cyt b與COI基因串聯作為分子標記，探討小鰭鰭尾鯙之族群遺傳結構，並以矢狀石之微細結構估計PLD日齡，輔以輪寬及鍶鈣比的時序變化，探討其早期生活史之漂送機制。結果顯示，小鰭鰭尾鯙擁有高單倍型歧異度 (h) 及低核苷酸歧異度 (π) ，中性檢定之Fu’s FS各族群皆為顯著負值，代表族群有擴張的現象。重建最大似然親緣關係樹 (Maximum likelihood tree) 及最小關聯網狀圖 (Minimum spanning network) 皆顯示沒有明顯的分群。分子變異分析 (AMOVA) 顯示主要變異來自個體間，族群間遺傳分化指數 (ΦST) 介於-0.02476到0.12067之間。分子證據顯示小鰭鰭尾鯙曾經歷族群擴散，且各族群間基因交流順暢。PLD介於33到98天，將樣本分為三個不同緯度來分析，平均PLD日齡隨緯度往北有增加的趨勢，耳石平均成長率則相反，顯示小鰭鰭尾鯙初期成長速率可能受到水溫所影響。僅分析臺灣地區樣本數超過三十尾的族群 (石梯坪、基翬及黃金海岸)，發現臺灣東側兩樣點之平均日齡數 (51.8 ± 7.2及51.7 ± 7.9天) 顯著小於西南側的樣點 (57.6 ± 9.7天)，推測和臺灣東西側洋流系統的差異有關聯。綜合上述結果，小鰭鰭尾鯙利用狹首幼生 (Leptocephalus) 的長PLD使基因在東亞島弧間交流順暢，因此有高基因同質性 (Genetic homogeneity)，但海水溫度及洋流系統等環境因子可能影響小鰭鰭尾鯙的生活史特徵。

Pelagic larval duration (PLD) of demersal fishes may play an important role to shape adult distribution patterns and population genetic structures. However, the relationship between PLD and population genetic structure remains unclear for Uropterygius micropterus, which has wide distribution, local spawning, poor adult migration ability and narrow niche breadth. Population genetic structure of U. micropterus collected from 8 locations, 3 countries (Japan, Taiwan and Philippines) were analyzed using cyt b and COI genes of mtDNA. Microstructure of otoliths were examined to estimate the PLD and otolith growth rate to investigate the mechanism of larval dispersion. The results showed high haplotype diversity (h) and low nucleotide diversity (π). No population can be distinguished by maximum likelihood phylogenetic tree and minimum spanning network. The AMOVA results demonstrated that > 99 % of genetic variations occur within populations and values of pairwise ΦST ranged from -0.02476 to 0.12067, indicating little to no geographic population genetic structure. The daily increments for all samples ranged from 33 to 98 days. PLDs was shorter and otolith growth rate was higher for the eels collected in Philippines. Higher water temperature might explain the shorter PLD and faster growth rate. PLDs of two populations from eastern Taiwan (51.8 ± 7.2 and 51.7 ± 7.9 days) were significant shorter than the population from southwestern Taiwan (57.6 ± 9.7 days). This result was most likely caused by different ocean current systems between eastern and southwestern Taiwan.