冠羽畫眉替代育雛策略：亡羊補牢猶未晚矣

Abstract

競爭是生物間普遍存在的互動關係，在競爭中失利的一方，藉由替代策略能降低競爭的代價並爭取利益，讓劣勢者亡羊補牢。社會生物生活在群體之中，除了享有利益之外，同時也遭遇嚴重的社會衝突與競爭。然而現今研究對社會衝突鮮少有全面性的觀點，群體中替代策略的運用也少被提及，因此本研究藉由冠羽畫眉(Yuhina brunneiceps)的育雛策略，來了解劣勢者能否依照自身現狀而採用替代策略並建立雛鳥競爭與成鳥選擇兩項假說。結果發現，當成鳥個體餵食投資量較大時，次位階成鳥選擇餵食給體重較輕的雛鳥，而且低位階成鳥偏好以第二順位回巢，增加餵食給較弱勢雛鳥的機會，符合成鳥選擇假說；然而在一般狀況下，體重較重的雛鳥獲得食物的機會較高，符合雛鳥競爭假說。冠羽畫眉合作生殖的過程中有許多衝突，而經過產蛋期的競爭與孵蛋期的付出之後，高位階成鳥已佔有優勢，次位階成鳥在子代處於劣勢的狀態下採取對自己有利的餵食策略，提高弱勢子代的存活率同時增加自己的適存度。本研究為首次發現合作群體中的成員在屈居劣勢的狀態下，運用替代育雛策略爭取利益。社會生物的投資與利益分配，未來不應只侷限在繁殖與食物資源分配上的競爭，而須更廣泛地討論替代策略在整體利益上所扮演的角色。衝突解決機制是群體生活演化中重要的一環，當群成員為爭取利益而產生衝突時，冠羽畫眉的應對方式或許是其他社會生物的解決範本。

Competition is a common interactive relationship in nature. Subordinate attempts to “make the best of a bad job” by alternative tactics. Social animals receive benefits by living in groups, but also suffer from strong conflicts and competition. However, few researches have noted overall conflict resolutions and applications of alternative tactics in social groups. We investigated an alternative tactic selection in cooperative breeding species, Taiwan yuhina (Yuhina brunneiceps), and tested the nestling competition hypothesis and the parental selection hypothesis. Here we show when an individual invested higher effort in provisioning, the parents in different hierarchy fed different weight of nestlings, subordinates preferred lighter nestling while dominants preferred larger one. On the other hand, subordinate chose provisioning in secondary sequence to improve the resource intake of weaker nestlings. Though the results support parental selection hypothesis, food resource allocation depended on sibling rivalry. Larger nestlings scramble more food, which supports nestling competition hypothesis. This is the first time record that subordinates can improve fitness by alternative tactics in unfavorable condition. In the future, we should focus not merely on the meaning of alternative tactics in reproduction and resource allocation competition, but study more in whole fitness performance. In evolution of group-living, the social conflict resolution is important in group formation. Taiwan yuhina show a good instance for cooperation and conflict in intensing competition environment.