四個幽蟌(Euphaea)姊妹種粒線體基因作為族群遺傳及親緣關係分子標記的效能探討

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Title:	四個幽蟌(Euphaea)姊妹種粒線體基因作為族群遺傳及親緣關係分子標記的效能探討
Other Titles:	Population Genetic and Phylogenetic Utility of Mitochondrial Genes of Four Sibling Euphaea Damselflies
Authors:	鄭筠潔 Cheng, Yun-Chieh
Contributors:	劉少倫 Liu, Shao-Lun 生命科學系
Keywords:	負向選汰;正向選汰;有效族群大小;粒線體基因;基因效能;蜻蛉目 negative selection;genetic draft;effective population size;Mitochondrial genome;phylogenetic utility;Odonata
Date:	2016
Issue Date:	2016-10-20T08:07:07Z (UTC)
Abstract:	一直以來，經由母系遺傳的粒線體基因被認為是研究族群遺傳及系統發生學的有效分子標記。但近期研究卻發現粒線體基因或許並不適合此用途，原因有二：一、由於其經歷過頻繁發生的正向選汰，此時有利的突變及其相鄰的基因會被固定下來(genetic draft)，這種狀況的發生使得粒線體基因擁有比中性理論預期還低的遺傳多樣性。二、粒線體基因過快的演化速率使各分子間的親緣關係難以表現出來。但，這些研究通常都以較高階的分類群為主，粒線體基因在種間的效能表現如何仍有許多未知。本研究透過不同族群大小的兩對姊妹群幽蟌屬豆娘─E. formosa + E. yayeyamana；E. decorata + E. ornata─的8個核基因、13個粒線體基因來對選汰壓力及基因效能進行分析。結果顯示，粒線體基因較核基因受到更強烈的負向選汰影響，而負向選汰是影響這些豆娘粒線體基因及核基因演化的主因。粒線體基因無論是在成對距離的分化度、α值、簡約訊息位點、不變位點的比例及相對置換率這些基因效能參數上都比核基因還要為高。在這些參數的平均中，粒線體基因的非蛋白質轉譯區比蛋白質轉譯區擁有較高的解析度。另外，核基因的外顯子提供的資訊較內插子要少。在相關性分析上，A+T-rich及nad2這兩個粒線體基因表現得最好，並能提供最多的資訊。研究顯示粒線體基因適合用作族群遺傳及系統發生學的分析之用，但需考慮如何選擇基因。 The maternal inherited mitochondrial genes have been considered as efficient genetic markers for population genetics and phylogenetic studies. However, recent studies suggested that mitochondrial genes might not be suitable for these purposes because (a) these genes have lower genetic diversity than expected from neutral evolution due to fixation of beneficial mutations by frequent positive selection (i.e. genetic draft), and (b) these genes evolved too rapidly to represent phylogenetic relationships. Nevertheless, these studies primarily focused on analyzing higher taxa, leaving the utilities of mitochondrial genes on species level analyses largely unknown. In this study, we investigated the pattern of selection and phylogenetic utilities of eight nuclear genes and 13 mitochondrial genes in two pairs of sibling Euphaea damselflies (E. formosa of Taiwan + E. yayeyamana of Yaeyama Islands; E. decorata of SE Asia + E. ornata of Hainan Islands) with various population sizes. Our results showed that, comparing to nuclear genes, mitochondrial genes experienced stronger negative selection, which was the dominance force in the evolution of both mitochondrial and nuclear genes in these damselflies. Mitochondrial genes had higher rates than nuclear genes in the pairwise distance divergence, α (shape of gamma distribution), PI (parsimony informative site), Pi (proportion of invariant sites), and the relative substitution rate. Among the averages of parameters, the mitochondrial protein non-coding regions had higher resolution than mitochondrial protein-coding region. In addition, the exons of nuclear genes provided less information than the introns. Correlation analyses demonstrated that mitochondrial A+T-rich and nad2 genes performed better and were more informative. In conclusion, our results showed that mitochondrial genes are suitable for genetics and phylogenetic analyses, but the selection of genes need to be considered.
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