永澤蛇眼蝶生活史及蛇眼蝶屬近緣類群之分子親緣關係研究

Abstract

永澤蛇眼蝶Minois nagasawae (Matsumua)屬於鱗翅目(Lepidoptera)蛺蝶科(Nymphalidae)蛇眼蝶屬(Minois)。蛇眼蝶屬隸屬於眼蝶系列(‘Satyrus series’)，大多數種類主要分布在古北區(Palaearctic zoon)。永澤蛇眼蝶則是分佈在臺灣3000 公尺以上高山的孑遺物種。本研究分為三個章節，分別針對永澤蛇眼蝶的生活史及生態學、永澤蛇眼蝶的眼紋多形性之地理模式，及蛇眼蝶屬及眼蝶亞族的分子親緣關係進行探討。 第一章針對永澤蛇眼蝶的寄主植物、生物學及幼生期形態進行詳細探討。幼蟲寄主植物部分，兩種禾本科植物(Poaceae)包括川上氏短柄草(Brachypodium kawakamii)及髮草(Deschampsia caespitosa)為幼蟲寄主植物。雌蝶產卵行為方面，卵粒產下時自由掉落且未黏附於任何物體上。幼蟲發育歷經五個齡期，且具有休眠越冬行為，休眠齡期通常在一齡及二齡。永澤蛇眼蝶的生物學相較於分佈在溫帶地區的近緣種類蛇眼蝶M. dryas (Scopoli)具有一致性，顯示永澤蛇眼蝶即使分佈在以亞熱帶氣候為主的島嶼，仍保留了適應寒冷氣候棲地的生物特徵。 第二章進行永澤蛇眼蝶的眼紋多形性之地理模式研究，由於鱗翅目的眼紋形成與演化受到許多基因調控、環境因子及選汰作用的影響，長久以來受到許多不同生物學研究領域關切。永澤蛇眼蝶為一年一世代眼蝶，分布在臺灣3000公尺以上高海拔，成蝶主要發生於秋季，眼紋數目及大小呈現多型性。永澤蛇眼蝶為一世代性眼蝶，眼紋多型性顯然並非源自季節適應現象。研究於2003-2010年期間採集477隻永澤蛇眼蝶，分別來自中央山脈、雪山山脈及玉山山脈共15個地點，經由線性迴歸分析眼紋大小、眼紋數目及鳥啄痕數目與緯度、性別及環境因子(十年均溫、十年平均雨量及十年每月平均日照時數)之關係。結果顯示眼紋大小顯著具有緯度效應，緯度愈高眼紋愈大；眼紋數目與鳥啄痕的分析中，緯度與性別因子顯著具有交互作用，高緯度地區雌蝶的眼紋數和鳥啄痕數目較雄蝶多；十年均溫、十年平均雨量及十年每月平均日照時數顯著影響眼紋大小與數目的變異。永澤蛇眼蝶平均有42%個體具有鳥啄痕，野外觀察發現6種鳥類天敵，包括高海拔數量優勢之一的臺灣噪眉(Garrulax morrisoniana)，顯示永澤蛇眼蝶面臨相當程度的鳥類捕食壓力。本研究認為環境因子與鳥類天敵捕食壓力是造成眼紋大小與眼紋數目地理分布模式的因素。 第三章探討蛇眼蝶屬及眼蝶亞族之分子親緣關係。蛇眼蝶屬(Minois)為眼蝶亞族成員，該亞族成員廣分布於舊北區溫帶、亞寒帶至寒帶地區，是一群適應寒冷氣候的眼蝶。本研究利用粒腺體COI及COII基因及核染色體Ef-1α基因序列，並參考已發表之相關研究，新增蛇眼蝶屬、林眼蝶屬(Aulocera)、擬洒眼蝶屬(Paroeneis)及Karanasa latifasciata obscurior樣本建構眼蝶亞族之分子親緣關係。合併分析COI+COII+Ef-1α序列所得之MP、ML和BI樹形圖外觀大致上一致，但樹基部的節點支持度低，眼蝶亞族不同屬之間可分為5群，包括Aulocera+Paroeneis group、Neominois+Oeneis group、Brintesia+Arethusana+Minois group、Satyrus+Chazara+Pseudochazara group、Berberia+Karanasa+Hipparchia group。分佈於亞洲大陸Paroeneis屬的P. sikkimensis與林眼蝶屬(Aulocera)成員形成單系群，其中小型林眼蝶(Aulocera sybillina)與Paroeneis屬的P. sikkimensis的親緣關係較其他同屬成員為近，此一結果暗示林眼蝶可能為並系群(paraphyletic groups)，根據分析結果，我認為Paroeneis屬應與林眼蝶合併。各樹形圖皆支持蛇眼蝶屬為一單系群，永澤蛇眼蝶的姐妹群為蛇眼蝶(Minois dryas)，蛇眼蝶屬最近緣類群為Brintesia，其次為Arethusana，與Satyrus的關係較前兩者遠，此一結果支持了前人根據卵粒形態及落卵式(egg-dropping)產卵行為所提出的假說，証明在眼蝶亞族當中，落卵式產卵行為的演化為一次發生事件。

Minois nagasawae, a satyrid butterfly belonging to ‘Satyrus series’ mostly Palaearctic in distribution, represents a relict species inhabiting alpine zones in Taiwan. The life history of this species was unknown. In the Chapter, the researches were focused on its immature biology and morphology. Two species of grasses, namely Brachypodium kawikamii and Deschampsia caespitosa, were recognized as the larval hostplants. The present study also confirms that the eggs of M. nagasawae are dropped freely without attachment to substrate, and five instars are required for complete development of the larval stage. Obligate winter diapause occurs in the younger larval stage, mostly taking place during the first or second instar. Accounts on chaetotaxy of immatures for M. nagasawae are also provided. The recognized biology agrees well with closely related, temperate species M. dryas, suggesting that M. nagasawae retains biological traits adapting to cool habitats although it is restricted to an island dominant by subtropical climate. In Chapter Two, the geographical patterns of eyespot polymorphism of Minois nagasaeae were documented. Eyespot formation and evolution involve gene expressions, environmental factors and selection forces. It has been the subject of extensive investigations by many different biological disciplines. Minois nagasawae, an univoltine satyrid butterfly inhabiting alpine zones above 3000m in Taiwan, is on the wing from July through October. The peak of occurrence is in the autumn. Phenotypic plasticity in terms of number and size are found on eyespots in M. nagasawae, and this variation is apparently not caused by seasonal factors for this univoltine species. In the present study, 477 individuals of M. nagasawae were collected from 15 locations belonging to Central Mountain Ridge, Hsuehshan Mountain Ridge and Yushan Mountain Ridge from 2003 to 2010. The regression among response variables (eyespot size, number, beak marks) and predictor variables (latitude, sex, environmental factors) were calculated respectively. The results show that a latitudinal gradient of eyespot size exits. Eyespot size increases with latitudes. For eyespot number and beak marks, the interaction between latitude and sex is significant. Females in higher latitudes have more eyespot number and beak marks than those in males. Environmental factors are also significant predictor variables for eyespot size and number. There were 42% of M. nagasawae with beak marks, and six avian predators were recognized in the field, with Formosan Laughing Thrush Garrulax morrisoniana as one of the dominant species at high elevations. We concluded that environmental factors and avian predation are both contributed to geographical variation of eyespot in size and number of M. nagasawae. Minois is a member belonging to subtribe Satyrina (Lepidoptera: Nymphalidae: Satyrinae) which are wildly distributed in paleoarctic area. In the Chapter Three, we constructed the molecular phylogeny of Satyrina using partial mitochondrial COI gene and nuclear Ef-1α gene sequences to clearify the relationships between Minois and its related generic taxon. Based on previous researches, additional taxon are used including Minois, Aulocera, Paroeneis and Karanasa. Analysis of combined COI+Ef-1α sequences was done. According to our results, maximum parsiomony, maximum likelihood and Bayesian inference topologies are similar. Five groups are recognized within Satyrina including Aulocera+Paroeneis group, Neominois+Oeneis group, Brintesia+Arethusana+Minois group, Satyrus+Chazara+Pseudochazara group and Berberia+Karanasa+Hipparchia group. Karanasa latifasciata obscurior and K. padma are located in different groups. More information will be needed to clearify its phylogenetic relationship within Satyrina. Aulocera sybillina accompany with Paroeneis sikkimensis forming a monophyletic group suggested that Aulocera is paraphyletic group. Minois was formed within a well-supported monophyletic group and is sister group to Brintesia. M. dryas is sister to M. nagasawae. This result supported previous studies suggesting that Minois is related to Brintesia+Arethusana and the evolution of egg-dropping behavior had happened at least once within Satyrina.