六斑二齒魨在西太平洋族群結構之研究

Abstract

六斑二齒魨（Diodon holocanthus）是二齒魨科（Family Diodontidae）的成員之中最為常見，數量也最為豐富的物種，在全球各大洋的近岸海域以環熱帶的模式分佈。由於六斑二齒魨缺乏明顯的成魚播遷行為與長距離移動能力，一般推測在其遼闊的分佈範圍裡，會因為基因交流受到距離限制而使得不同地區的族群之間產生遺傳組成之差異。本研究係以粒線體DNA中的控制區域片段（control region）和細胞色素b（cytochrome b）基因來分析在西太平洋海域內，採集自台灣周圍、日本與兩者之間的六斑二齒魨個體，是否存在有能夠被偵測到的明顯族群結構。本研究以ΦST和AMOVA分析方法比較各區域之間遺傳組成之差異，建立序列之間的親緣關係樹狀圖和單倍體基因型（haplotype）之間的網狀結構，並進行變異分佈分析（mismatch distribution）與族群歷史的估算。研究結果顯示台灣與日本的族群之間並不存在顯著的遺傳差異，並且無法偵測到明顯的族群結構，顯示可能在不同地區的族群之間的基因交流並無受到距離限制，推測存在有促進基因交流的機制，例如甚長的漂浮仔稚魚期（pelagic larval duration），或是族群曾經歷過如冰河期等的歷史事件導致的遺傳組成均質化（genetic homogenization），使得族群分化的程度在此區域內並不顯著。

The long-spine porcupinefish (Diodon holocanthus) is the most common and abundant species among all members of family Diodontidae, which has the circumtropical distribution pattern. As a marine fish with such wide geographic range but without known dispersal mechanism and the capability of long-distance migration, it is suspected that gene flows between populations of D. holocanthus should be limited, and thus in recognizable genetic differentiations among populations. We used the mitochondrial control region (D-loop) and cytochrome b (Cyt b) sequences to investigate whether the geographical structure exists among populations from Taiwan and Japan, within Western Pacific waters. The F-statistics analysis and AMOVA were applied for to detect genetic differences between populations. Phylogenetic trees and haplotype networks were constructed to elucidate the relationship among haplotypes. Demographic changes in the past were also addressed by analysis of mismatch distribution, as well as coalescence estimations. The result shows that the genetic difference between populations of different locations is insignificant. It indicates that gene flows between different populations are not limited by the geographical distances between sampling sites. Mechanisms may exist to enhance gene flows and thus prevent genetic differentiation, such as extended pelagic larval duration.