Cyclommatus Mniszechi

國立臺灣師範大學理學院生命科學系碩士論文 Department of Life Science College of Science National Taiwan Normal University Master’s Thesis 雄性二型雞冠細身赤鍬形蟲之異速生長與打鬥評估策略 The allometry and fighting assessment strategy of male dimorphic Cyclommatus mniszechi 陳震邑 Chen, Zhen-yi 指導教授 Advisor：林仲平博士 Ph.D. 中華民國 109 年 2 月 February 2020 致謝感謝我的指導教授林仲平老師在這三年多來的教導、支持與鼓勵，讓這篇研究可以成形，並依序架構出實驗架構的輪廓，幫助我在研究之路上可以理出下一步的方向。同時也感謝許鈺鸚老師與打鬥行為實驗室的各位成員，在每次的實驗室會議中對於實驗設計與統計分析方法的建議與在實驗空間的協助，提供理論與實務上的建議，讓打鬥行為實驗可以順利的完成並分析出結果。感謝親愛的實驗室夥伴們與各位朋友們，陪我進行野外採集、蒐集樣本、實驗室飼養、操作實驗，也陪伴我在這段時間學習以外的時候可以盡情的休閒，排解壓力，抒發心情，最後感謝我摯愛的家人，在求學的這段時間給予物質與精神上的支持，讓我可以專心地完成這份論文。 I 摘要雄性鍬形蟲具有誇張的大顎作為打鬥時獲取食物與繁殖資源的武器，大顎武器的形狀與大小可能會影響打鬥的行為與勝負。本研究檢測雞冠細身赤鍬形蟲(Cyclommatus mniszechi)的異速生長關係、打鬥行為序列和打鬥評估策略。首先，大顎與體型之間的異速生長關係的判定可以用來作為決定不同型雄蟲的基礎，再者，藉由行為序列分析來描述依大顎大小隨機配對與對等配對的雄蟲間打鬥的行為序列，最後，從打鬥時間(和激烈程度)與資源佔有潛力(RHP, resource holding potential)的相關性來檢驗不同評估策略(自我、累加和相互評估策略)的預期。異速生長的分析結果顯示大顎長與體長之間存在非線性正異速生長關係，且在體長(翅鞘長)為 15.03 毫米時為異速生長係數改變的轉折點，可以此將鍬形蟲個體分為大型與小型雄蟲。從打鬥行為序列中可以定義出九種行為單元，包含「觸碰」、「防衛姿勢」、「抬身對峙」、「攻擊」、「推擊」、「纏鬥」、「抓取 1」、「抓取 2」(抓取於對手胸節或腹節)以及「撤退」。大小型雄蟲具有不同的打鬥行為序列，小型雄蟲傾向持續待在相同打鬥階段(較多在同一個打鬥階段內的行為轉換)，相對於大型雄蟲則較容易進入纏鬥階段。大顎長對於打鬥結果有決定性的影響，可以做為代表雞冠細身赤鍬形蟲的資源佔有潛力相關的可靠特徵。在隨機配對打鬥 II 中，打鬥時間與勝者及敗者的大顎長有顯著正相關，顯示自我評估可能為此種鍬形蟲所採用的打鬥評估策略。在對等配對打鬥中，打鬥時間與平均大顎長有顯著正相關，進一步支持鍬形蟲採用自我評估策略。然而，雄蟲在打鬥中出現對手之間的對等行為，呈現多次但很少造成傷害的身體接觸，與單方向的行為階段進程(由低度至高度激烈且鮮少逆向的打鬥階段)。因此，雞冠細身赤鍬形蟲的打鬥可能不僅使用自我評估策略，累加與相互評估策略可能也在其打鬥決策中扮演重要角色。關鍵字：體型、雄性競爭、資源佔有潛力、行為序列分析、性擇、武器 III Abstract Male stag beetles (Coleoptera: Lucanidae) possessed exaggerated mandibles as weapons used in fighting contests for access to food and reproduction. The shapes and sizes of these mandibular weapons could influence the fighting behaviours and outcomes of the contests. This study examined the allometry, fighting behaviour and assessment strategy of a stag beetle, Cyclommatus mniszechi. Firstly, the allometric relationships between mandible and body sizes were identified to determine whether the males could be grouped into different morphs based on the allometries. Secondly, the behavioural sequences of male- male fights were characterized using sequential analyses of randomly and size-matched contests. Finally, the correlational predictions between contest duration (and aggressiveness) and RHP (resource holding potential) were examined to test alternative assessment strategies (self-, cumulative and mutual assessment). Allometric analyses show a nonlinear positive allometry between mandible and body size in C. mnizechi males, and that they consist of dimorphic males defined quantitatively as the majors and minors by body sizes at the switch point of elytra length of 15.03 mm. Nine behavioural elements were identified from the contests, including ‘touch’, ‘defensive posture’, ‘body raising’ ‘attack’, ‘push’, ‘tussle’, ‘clamp1’(head), ‘clamp2’ (thorax or abdomen) and ‘retreat’. The major and minor males have different fighting behavioural sequences, where the minor males tend to stay within phases (more behavioural transitions within phases) of the contests and more likely to tussle than the major males. Mandible size is the main determinant of the outcomes IV of the contests and can be used as a reliable proxy for RHP in C. mnizechi. In randomly matched contests, strong positive relations between contest duration and winner’s and loser’s mandible sizes indicate that self-assessment determines strategic decisions in C. mniszechi. In size-matched contests, a positive relation between contest duration and mandible sizes further support the self-assessment strategy. However, males showed behavioural matching in contests, many physical contacts with rare injuries and unidirectional behavioural progressions in phases (from low towards high aggression with rare de-escalation). Therefore, the fighting contests of C. mniszechi may not settle entirely on the basis of pure self-assessment, and that cumulative or mutual assessment may also play an important role in contest decisions. Key words: Body size, male-male competition, resource holding potential, sequential analysis, sexual selection, weapon V Ta ble of Contents Introduction………………………………………………………………1 Materials and methods………………………………….…………….......9 Study organism………………………………………………………9 Insect rearing……………………………………………………10 Morphological measurements………………………………………11 Allometry analyses………………..………………………………12 Fighting contests………………………………………………… 14 Determination of traits associated with RHP.………………………15 Sequential analyses of fighting behaviours…………………….…16 Statistical analyses of RHP, aggression and contest duration………17 Results……………………………….………………………………...18 Morphological measurement and allometric analyses…………….18 Behavioral sequence of fighting contests…………………………19 Male morph and contest aggression………………………….…..23 Contest duration and RHP………………………………………...24 Discussion…………….…………………………………………………24 Dimorphic males, allometry and fighting behaviours……………….24 Self and mutual assessment strategy…………………………….....27 Probable mechanisms of assessment in C. mniszechi stag beetles…30 References…………………………………………………………….33 VI List of Tables Table 1. Behavioural elements of the contest interaction………………..39 Table 2. Correlation of the relationships between morphological traits….40 Table 3. Models selection of the allometry analyses……………………..41 Table 4. Parameters estimated for the isometry tests……………….……42 Table 5. Relationships between aggressiveness and morphological traits in randomly matched contests……………………………………………...43 Table 6. the correlation between contest duration and male morphs and average mandible length in the size-matched contests…………………44 VII List of Figures Figure 1. Mate-guarding, male morphs and morphological measurements of Cyclommatus mniszechi ………………………………………….…45 Figure 2. The allometric relationship between ln-transformed mandible length and elytra length………………………………………………..46 Figure 3. The fighting arena of Cyclommatus mniszechi……………… 47 Figure 4. Sequential analyses of contest behaviours in randomly and size- matched contests……………………………………………………….48 Figure 5. Ethograms and sequential analyses of behabvioural elements of major and minor male of Cyclommatus mniszechi…………………..……..49 Figure 6. Logistic regressions of contest behaviours…………………….50 Figure 7. Simple linear regressions of contest behaviours………………51 VIII List of Supplementary Information Table S1. The information of Cyclommatus mniszechi specimens………52 IX Introduction Male of many insects use weapons to compete for resource essential for their survival and reproduction (Emlen 2008b). Sexually selected traits such as ornaments and weapons often evolve to reach greater extremes of size and elaboration (Andersson 1994; Darwin 1871; Emlen 2008a; Emlen and Nijhout 2000). Males of many insects use enlarged weapons to compete for their survival and reproduction (Emlen 2008a). One group of insects with an amazing diversity of weapons are stag beetles (Lucanidae). Male stag beetles use their exaggerated mandibles as weapons to fight for the access to the sap site, territory and females (Emlen 2008a; Goyens et al. 2015a; Goyens et al. 2015b; Inoue and Hasegawa 2012; Songvorawit et al. 2018). Mandible and body size are reliable indicators for male stag beetle’s resource holding potential (RHP) and positively correlate with their ability to win the contests (Goyens et al. 2015a; Kuan 2011; Songvorawit et al. 2018). Stag beetles exhibit a high diversity in the sizes and shapes of mandibles both within and across species (Emlen 2008a; Kawano 2000; Mizunuma and Nagai 1994; Shiokawa and Iwahashi 2000), which may cause the behaviours they display in fighting to be highly variable (Emlen 2008a). The scaling relationship or allometry of trait size and body size is informative for many important aspects of organism’s biology such as polyphenism (Rowland and Emlen 2009), alternative reproductive tactics (Tomkins et al. 2005) and nature of selection on different body parts (Bonduriansky 2007; Kojima and Lin 2017). The allometry of sexually selected traits can be positive (slope > 1), isometry (slope = 1) or negative 1 (slope <1), and often reflects resource-allocation trade-offs, balance between natural and sexual selection, and genetic constraints of these traits (Bonduriansky 2007; Bonduriansky and Day 2003). The mandible and body size in many stag beetles show a linear and positive allometry, in which larger males have relatively larger mandibles than those of smaller males (Clark 1977; Huxley 1931; Kawano 2000; Knell et al. 2004; Romiti et al. 2015). The positive allometry is explained by greater fitness advantages for larger males to invest proportionally more in the development of weapons versus other body parts (Emlen and Nijhout 2000). Nonlinear (curved, sigmoid or discontinuous) allometric relationships between mandible and body size have also been reported for stag beetles (Emlen and Nijhout 2000; Kawano 2000; Knell et al. 2004). The declined slope of the curved allometry in the largest males is likely due to the depletion of resources available for the development of the weapon, resulting from the competition of imaginal disc within closed pupal chamber (Knell et al. 2004; Kojima and Lin 2017; Nijhout and Wheeler 1996). The sigmoid and discontinuous allometries are characterized with the evolution of size-dependent, alternative reproductive tactics (Andersson 1994). For examples, in dung beetles the larger and horned males use a mate-guarding and fighting strategy against opponents, whereas the smaller and hornless males employ a sneaking tactic for access to females in guarded

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