生態及社會因子對冠羽畫眉（Yuhina brunneiceps）偶外配對的影響

Abstract

偶外配對（Extrapair copulation）是一夫一妻制物種間常見的行為，目前研究多從增加子代遺傳上間接利益的角度來探討偶外配對的成因，對其他因素的探討較缺乏。冠羽畫眉（Yuhina brunneiceps）與非親戚行共用一巢制合作生殖，故有更多偶外配對的機會遇到潛在偶外配對對象：冠羽畫眉的子代有27.55%是偶外配對子代所生，其中58%的偶外配對子代是跟同繁殖群的異性所生。本研究分析2001年、2003-2007年繁殖季探討生態因子與社會因子如何影響冠羽畫眉偶外配對的機率，其中生態因子包括雨量、氣溫，社會因子則包括群大小、親鳥位階、親缘關係。結果發現因子發現降雨少（環境好）時，次位階雌鳥產出偶外配對子代的機率高於高位階雌鳥；降雨多（環境差）時，偶外配對子代出生機率很低，但與親鳥位階沒有關係。親緣關係分析結果顯示雌鳥若與配偶親緣關係較近，則與親緣關係較遠的群外個體發生偶外配對的機率升高，且群外偶外配對的結果會有較高機率生出雄性子代。研究結果顯示，因為生態因子對不同位階親鳥的直接利益有不同的影響，故偶外配對的發生機率也同時受生態因子與社會因子影響，個體在決定是否尋求偶外配對時，會同時權衡未來子代的利益，以及自身當時需付出的成本。

Extrapair copulation（EPC） is a common behaviour in monogamous species, the current researches usually infer that EPC is for gaining indirect benefit like improving offspring genetic quality, but lack of discussion about influences from other factors. Taiwan Yuhinas （Yuhina brunneiceps） cooperate with unrelated individuals for joint-nesting, they have more chances to meet potential extrapair mate：27.55% of Taiwan Yuhina offspring are extrapair offspring（EPO）, and 58% of EPO are born with individuals in same breeding group. This research analyses the influence to the probability of EPO from ecological factors and social factors, data is from breeding season in 2001, 2003-2007. Analysis by ecological factors include precipitation and temperature, social factors include group size, hierarchy, relatedness. The result shows subordinate females tend to have more EPO with fewer precipitation, but among different hierarchicval females there’s no significant of having EPO while with more precipitation. Another result shows if a female has a more related social mate, there is more probability to seek intergroup EPC with more unrelated individuals outside the groups, and the intergroup EPO have more probability to be male. These results indicate that EPC affected by social factors and ecological factors simutaneously, and lower hierarchical females tend to seek EPC when the environmental condition is better, so ecological factors play important roles on parents-gaining-direct benefits, seeking EPC shall find a balance between the benefit for offspring and cost of parents.