鰏科魚類的外型發育與DNA條碼特性及鑑定上之應用

Abstract

鰏科魚類為一群廣泛分布於印度-太平洋之小型至中型的海水硬骨魚，在臺灣為魩鱙漁業主要的混獲魚種，且已鑑定有九屬十八種。 明確的鰏科魚類分類對於鰏科物種的保存及沿岸生態系的維護有十足貢獻；然而，由於鑑定上的困難使鰏科魚類之幼魚時期物種組成，以及種間類源及生態上的關係仍亟待釐清。 為了幫助物種鑑定，本實驗中使用Size-free discrimination分析方式來檢測物種特有的形狀(shape)，以及使用分子條碼技術來量化物種間的DNA特性。 在實驗方法上，三種不同生活史階段的樣本皆用以進行分析，在實驗最後根據其形態測量以及分子分析的結果來推測可能的親疏關係，並將鑑定上之關鍵特徵賦予類源上的意涵。 不同物種間尺寸因素完全移除後之形狀參數和傳統上依照外形來做分類的結果互相一致，但僅限於稚魚期與成魚期；對於幼魚而言，物種特有之形狀在形成階段並無單一特徵參數提供鑑定使用，但相似物種則有一系列之相似陣列，提供祖先型之特徵。 在分子方面同屬之物種其屬內平均遺傳距離為0.036，屬間差異則為0.197，而同物種之個體期平均遺傳距離為0.017，種間則為0.187，兩者比值為11.2，此結果顯示COI之差異對於鰏科魚類的物種鑑定十分有效，為一種相當具有潛力的鑑種工具，並可輔助外型鑑定上的不足。 由支序圖的結果可看出由COI基因序列所組成的標準生命條碼，對於同一屬內的物種關係具有強力的鑑別能力，但不同屬間的關係其可信度較低(Bootstrap value < 70)，因此由樹型所導引的鑑定具有解釋上的意義。 總體而言，就實驗的結果來看形質測量和生命條碼對於鰏科魚類的物種鑑定十分有效，且發揮相輔相成的關係，但在外部形狀差異與COI基因分歧方面，兩這並無顯著相關性，僅Secutor與Gazza顯示大致相符的結果，即在外形和分子間存有高度相關性。換句話說，Secutor 與 Gazza相對於他屬鰏科魚類，在演化出現的時間較早，其它鰏科魚類則較晚，且種化較快，這點可作為進一步研究的著眼點。

Ponyfishes are members of Leiognathidae, which are small-sized coastal fishes distributed in Indo-Pacific. In Taiwan, nine genera and eighteen species were found, and they become significant by-catch species in larva fisheries. Clear leiognathid taxonomy could benefit to their conservation and coastal ecosystems but the catch composition of ponyfishes, especially for larvae is still unknown due to problematic species description. To facilitate species identification, in this study I used the morphometric analyses to estimate species-specific shape and the molecular barcoding technique to quantify DNA differences. All development stages (larva, juvenile and adult) are analyzed when samples were available and subsequently, their similarity was also elucidated based on morphometric and molecular findings. Inter-specific differences due to sheered shape (size factor clearly removed) echoed the relationship obtained from traditional morphological analyses for juvenile and adult but did not applied to larval stage due to the shape score of different species are mixed and without significant gaps. In molecular aspect, the mean distance within congeneric species is 0.036, and inter-genera difference is 0.197, and the distance among the same species is 0.017, the distance between different species is 0.187, with the ratio of 11.2 between inter-/intra-specific distances indicated that COI barcoding could be an effective tool to identify ponyfishes when morphological difference is insignificant. The use of consensus COI as species standard barcode is considered powerful. In general, in our results, the morphometry and DNA barcoding technique are very powerful in ponyfishes’s identification and can be complement to each other. In the results of morphological changes and the differentiation of mutation of COI, they are not significant related, but the status of genus Secutor and Gazza show high-correlation in two analyses, which means that the relationship between genus Secutor and Gazza to the Leiognathus complex can be further investigate in the further.