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  • 學位論文

合作與競爭對社會性動物壓力之影響

Effect of Cooperation and Competition on Stress Response in Social Species

指導教授 : 袁孝維
共同指導教授 : 沈聖峰(Sheng-Feng Shen)

摘要


生物需應付來自環境與社會中的各種壓力源,在生理與行為上調適以維持生存,藉由壓力荷爾蒙皮質素,Glucocorticoid,簡寫GC) 分泌提高個體的適存度。然而長期分泌可能造成個體免疫力與生殖力下降,因此瞭解影響生物壓力來源的因子有其重要性。對社會性動物而言,除生態因子 (如食物資源) 外,社會因子 (如社會位階) 與壓力荷爾蒙的關係,更是過去研究的重心,但對兩種因子交互作用的影響則鮮少被探討。本研究於2010與2011年繁殖季 (4~8月) 於台大梅峰農場進行,透過量測行合作生殖的燕雀目鳥類-- 冠羽畫眉 (Yuhina brunneciceps)體內的腎上腺皮質酮 (corticosterone;CORT) 濃度作為壓力指標,探討合作群體中「個體投資」和「社會競爭」兩個假說架構下,如何影響個體的壓力反應。根據個體投資與社會競爭兩種假說,分別測試包括群大小、繁殖階段、位階、性別、親緣關係、性別比例、群穩定性、雨量與親緣關係與壓力荷爾蒙分泌之關係。野外觀察得知個體群大小、位階、繁殖階段以及群成員變動因子,並於實驗室分析CORT濃度、性別以及親緣關係因子。結果顯示個體投資確實是造成個體壓力的主因:1. 育雛期CORT值顯著高於築巢及孵蛋期;2. 低位階較高位階的CORT值高;3. 與群內親緣關係近的個體,隨著雨量增加個體的CORT值越高;親緣關係較遠的個體CORT值則不會受到雨量影響。因此,本研究發現社會性生物的壓力變化主要受到個體的投資影響,且社會因子會與生態因子交互作用影響壓力反應。

並列摘要


Understanding how ecological and social factors might affect individual stress level is essential because the physiological stress response could have fitness consequences. Most studies have focused on how social factor, particularly dominance, is related with stress response in social species by measuring Glucocorticoids (GC). However, the relationship between dominance and stress hormone varied across taxa and the underlying mechanism is unclear. Moreover, few studies have considered how ecological factors might interact with social factors to affect stress response. Here we tested the effect of ecological and social factors on CORT secretion under two hypothesis frameworks, investment hypothesis and social competition hypothesis, using a joint-nesting passerine species, Taiwan Yuhina (Yuhina brunneciceps). Theory predicts that individuals in a cooperative unit should have higher stress response when investment or competition is higher, which then lead to testable predictions associated with ecological factors (rainfall in our study) and social factors (group size, breeding stage, hierarchy, gender, sex ratio, relatedness, and group stability). We conducted this study during breeding season (April to August) in 2010 and 2011 in the high elevation Meifen Experimental Farm, Taiwan. First, we found that the subordinate individuals (gamma) had higher CORT level than the dominants (alpha and beta). Secondly, CORT level was highest in the provisioning stage and lowest in the incubating stage. Thirdly, during unfavorable environment (higher rainfall days), individuals that are more related with the breeding group had significantly higher CORT levels than those that are relatively less related. Our results indicated that the role of investment is more important than competition in the joint-nesting system. Furthermore, ecological factors could interact with social factors and together affect the stress response, which has been largely ignored in the past.

參考文獻


陳潁慧 (2007) 冠羽畫眉之偶外配對繁殖策略。國立台灣大學生物資源暨農學院森林環境暨資源學系碩士論文。
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