疣胸琉璃蟻的親緣分析、種內攻擊行為與分類修訂之研究

Abstract

入侵種生物常會負面影響被入侵區域的生物群聚與生態系統服務，因此，了解生物入侵的機制有利於生態系的管理和保育。入侵種螞蟻是這些外來生物中分布最廣，也是破壞力最強的類群之一。在螞蟻成功入侵的案例中，入侵族群可能會表現出異於原生族群的行為，例如在新入侵的棲地形成「超級聚落」，允許同種的個體在各個巢穴之間移動和交流，且不會引發攻擊行為。本研究聚焦在台灣的疣胸琉璃蟻 (Dolichoderus thoracicus)，這種螞蟻廣泛分佈在台灣及其他的東南亞地區，並被分為七個有效的亞種。雖然過去疣胸琉璃蟻並未被視為害蟲，但近年來在台灣部分地區有族群爆發現象，造成淺山地區居民生活上的困擾。為探討疣胸琉璃蟻族群在台灣爆發的原因，本研究於第二章先分析台灣和東南亞疣胸琉璃蟻族群間的親緣關係，以釐清台灣近期的族群爆發現象是否源自於非原生族群的入侵；接著在第三章透過同伴識別行為實驗，調查台灣爆發的疣胸琉璃蟻族群是否已形成超級聚落；第四章則進行疣胸琉璃蟻的分類回顧，並以系統分類學的角度探討疣胸琉璃蟻不同亞種的分類地位是否合宜。 本研究的主要研究結果顯示： (1) 台灣和東南亞的疣胸琉璃蟻具有兩個主要的粒線體支系，支系一的疣胸琉璃蟻在台灣廣泛分佈，由六個與菲律賓樣本相似的單倍型基因組成，根據親緣關係樹，這些琉璃蟻很可能自菲律賓自然擴張而來。相較之下，近期族群爆發（台灣中部）的疣胸琉璃蟻屬於支系二，這些琉璃蟻僅有一個的單倍型基因，遺傳多樣性低，且與其他中南半島收集到的樣本相同，因此，在台灣爆發的疣胸琉璃蟻（支系二）很可能源自於近期的入侵事件。(2) 綜合親緣分析及行為實驗的結果顯示，台灣中部地區的疣胸琉璃蟻族群共分成三個聚落，支系一的疣胸琉璃蟻分為兩個小聚落，但支系二的入侵族群形成了一個超級聚落，涵蓋面積約有128,000公頃，此為疣胸琉璃蟻可形成超級聚落的第一筆科學資料。(3) 東南亞的疣胸琉璃蟻的七個亞種地位均需要重新調整，其中D. t. emarginatus、D. t. lacciperdus和D. t. nasutus應被視為疣胸琉璃蟻的次同物異名； D. t. borneonensis應被提升至種的階級，另D. t. bilikanus，D. t. rufescens及D. t. levior則應被視為此物種的次同物異名。依據粒線體COI序列重建的親緣樹，本研究發現疣胸琉璃蟻主要分為兩個遺傳支系，進一步檢查兩支系樣本間的形態特徵，由於差異不大，因此不採用粒線體COI的遺傳差異進行亞種劃分。最後，本研究分別根據形態及遺傳資料，認為同屬的D. lactarius和D. rugocapitus也應被視為疣胸琉璃蟻的次同物異名。 綜合以上結果，本研究顯示台灣有非原生族群的疣胸琉璃蟻入侵，可解釋台灣近期的疣胸琉璃蟻爆發事件，此機制（非原生族群入侵）可能是重要但被忽略的生物入侵、族群爆發機制；另外，相較於台灣原生的疣胸琉璃蟻族群，入侵族群可形成超級聚落，了解這種行為可塑性不但可以釐清其入侵成功的機制，也有助於未來擬定相關的管理方針及防治策略；最後，本研究重新修訂東南亞地區的疣胸琉璃蟻分類，這將有助於東南亞地區蟻科的生物多樣性研究、都市昆蟲學研究及農田生態管理工作。

Invasive species usually negatively impact local communities and ecosystem services in invaded habitats. Therefore, a deeper understanding of invasion mechanisms should benefit ecosystem management and conservation. Invasive ants are among the most widespread and damaging groups of introduced species. In the case of successful ant invasions, some introduced populations may behave differently from the native ones. For example, introduced ant populations may form a large supercolony in invaded habitats, allowing individuals to move and communicate among nests without eliciting aggression against conspecifics. In Taiwan, the black cocoa ant, Dolichoderus thoracicus (Smith), has never been considered as a pest in Taiwan until the recent outbreaks in central Taiwan. Therefore, this study aimed to review this species and examine the underlying mechanism for its outbreaks in Taiwan via analyses in phylogeny and aggression behavior. To do so, this study (Chapter Two) tested if an introduction of non-native lineage(s) may contribute to the sudden outbreaks of D. thoracicus in Taiwan by analyzing the phylogenetic relationships between Taiwan and Southeast Asia populations. This study (Chapter Three) then conducted behavioral experiments (intraspecific aggression assays) on different D. thoracicus populations in Taiwan, in order to examine whether D. thoracicus has formed a supercolony in Taiwan. Finally, this study (Chapter Four) reviewed the taxonomic revision of D. thoracicus and revised the subspecies status of D. thoracicus using systematics. The main findings of this study include the following: (1) All D. thoracicus in Southeast Asia can be grouped into two major mitochondrial clades (Clade I and II). Clade I is widespread in Taiwan and represented by six haplotypes that are genetically similar to the haplotypes from the Philippines (with higher diversity), indicating that these Clade I ants in Taiwan are likely a result of range expansion of the Philippine lineage. In contrast, ants from central Taiwan harbor a single Clade II haplotype that is predominantly found in the samples collected from the Indochina region. Because of the low genetic diversity, Clade II in Taiwan was most likely introduced from the Indochina region. (2) Based on the phylogeny analysis and behavioral experiments, this study reveals that Clade I consisted of two small colonies, but Clade II formed a supercolony in Taiwan. This Clade II supercolony roughly covered an area of 128,000 ha — the first scientific record of supercolony established by D. thoracicus. (3) This study has revised the taxonomic status of the previous seven subspecies of D. thoracicus in Southeast Asia. Three previous subspecies, D. t. emarginatus syn. n., D. t. lacciperdus syn. n. and D. t. nasutus syn. n., are now regarded as junior synonyms of D. thoracicus; D. borneonensis stat. n. is now raised to species level from subspecies and includes three junior synonyms (D. t. bilicanus syn. n., D. t. rufescens syn. n. and D. t. levior syn. n.). Moreover, two species (D. lactarius syn. n. and D. rugocapitus syn. n.) are now regarded as junior synonyms of D. thoracicus by morphological and phylogenetic evidences, respectively. In conclusion, this study first suggests the invasion of non-native lineage as a mechanism for the recent outbreaks of D. thoracicus in Taiwan, highlighting a potential research avenue for future research on the association between the “pest” trait and non-native genetic variant in invaded area. Second, this study reveals a formation of the supercolony in the non-native populations of D. thoracicus in Taiwan. This reported behavioral plasticity not only help explain the successful population or species invasion, but also help provide insights for management policies and control strategies. Third, this study revises the complicated subspecies status of D. thoracicus and sould benefit future works on the entomological, agricultural, and ecological topics of this species in Southeast Asia.