以分子演化探討海葵魚之系統發生學

Abstract

海葵魚主要分佈於印度太平洋海域，其分類位階屬於雀鯛科 (Pomacentridae) 中的海葵魚亞科 (Amphiprioninae)，所有海葵魚種類共計29種。海葵魚鮮豔的體色及特殊與海葵共生的生活習性，使其極受到水中攝影者及水族玩家的喜愛。 魚類傳統的分類學是以多種形質、棲地、生活史或是生物特性作為判別依據，凡舉體型、體長、骨骼、肌肉、鰭條數、鱗片、側線、鰓耙數、器官等皆可用來區分魚種的形質，但形質常常因為一些外在因素造成改變。許多珊瑚礁魚類主要是用體表顏色及花紋來鑑別，但分子遺傳研究結果顯示，體表顏色及花紋不足以證明遺傳隔離以及種的界定。海葵魚大部分形質十分相似，且其體表顏色及花紋會隨著地理區隔而有所不同，海葵魚相似種 (sibling species) 的外部形態十分相似，單純使用形質鑑別海葵魚有一定的困難度。此外，外部形質的判定也有可能因為鑑定者的主觀意識而有不同的鑑定結果，也增加傳統分類學鑑定的不確定性。近年來因分子生物學及生物化學技術的發展，分析物種分類及親緣關係的研究技術不斷地被突破與改良，提供更多依據來增加鑑別魚種客觀性。 本研究使用海葵cytochrome b基因序列，對於24種海葵魚進行種間之系統發生學分析，以最大似然法 (Maximum Likelihood, ML) 和鄰近法 (Neighbor Joining, NJ) 建構出海葵魚親緣關係樹狀圖，結果顯示可將海葵魚分成三群：I群所包含海葵魚物種為不同地區之克氏海葵魚 (A. clarkii)，III群所包含海葵魚物種屬於Actinicola亞屬及A. biaculeatus，其餘的海葵魚物種皆歸類於II群。和先前研究以最大儉約法 (Maximum Parsimony, MP) 和貝氏推導 (Bayesian inference, BI) 建構出海葵魚親緣關係樹狀圖結果一致。 先前海葵魚親緣關係之研究指出，Amphiprion屬及Premnas屬是單系群 (Monophyly)，所以提出將Premnas屬併入Amphiprion屬中之建議，本研究結果也支持將Premnas屬併入Amphiprion屬中。 單純以海葵魚外部形態不可做為海葵魚親緣關係分類之依據，因此本研究以分子證據闡述海葵魚之親緣關係並用傳統的形態分類法作為輔助，提出一具有親緣關係之海葵魚檢索表，以供海葵魚後繼研究者參考。

Anemonefish live in tropical coral reefs or shallow lagoons of the Pacific Ocean and Indian Ocean. Anemonefish are fish from the subfamily Amphiprioninae in the family Pomacentridae. Anemonefish, namely Amphiprion, are presently subdivided into the 29 species. Because of the diversity of their body colour patterns, they are quite common and popular, not only in the field of underwater photography, but also in the seawater ornamental fish trade. The traditional fish taxonomy is mainly based on a wide range of traits, say shapes, habitats, life histories, and other biological characteristics, as the basic input for species delimitation analysis. However, these traits are not always stable during their life cycle, and are possibly variable within the same species. Many coral reef fish species are identified according to their colour patterns. However, recent molecular genetic studies have shown that the colour pattem is not appropriate for use as the morphological marker for the investigation of population genetic isolation or species boundaries. The genus Amphiprion comprises several species that have very similar colours. Additionally, morphological characters are often variable and the colour types could be very different in different geographical locations, and sometimes sibling species share a considerable overlap of morphological characters. Therefore, to classify or identify anemonefish had made the taxonomist greatly perplexed. In this research, we studied 24 out of 29 anemonefish species by analysing cytochrome b (Cyt b) gene sequences, so as to reconstruct their phylogenetic tree through Maximum Likelihood (ML) and Neighbor Joining (NJ) methods. The results support how there should be a monophyletic origin for the subfamily Amphiprioninae, and that there are three distinct genetic groups within anemonefish species according to both the molecular and morphological evidences, but also that the two genuses, Amphiprion and Premnas, belong to the monophyletic group. Moreover, we create an identification key, combining the information of phylogenetic tree and morphological characters, which could be regarded as a reference for the anemonefish studies in the future.