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The allometry and fighting assessment strategy of male dimorphic Cyclommatus mniszechi
resource holding potential
|Abstract:||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。|
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 non-linear 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 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.
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