倉鼠也行社會性訊息襲取且會引發觀察學習當下以及事後的改變

Abstract

觀察學習，意指生手透過觀察他人的行動進而習得新的行為或訊息，這種學習方式已在不同物種的諸多行為中被證實過。透過觀察他人的社會互動進而從中萃取出訊息的這種學習方式被稱為社會性訊息襲取；過去相關的研究大多針對人類以及某些魚類與鳥類，但針對人類以外的哺乳類動物還未曾有過。利用敘利亞雄性倉鼠具有之領域攻擊行為，我們發展出一個行為操作方法來探討社會性訊息襲取。本論文中共有三個主實驗，目的在探討觀察者連續三天對兩個示範者的打鬥或中性事件進行觀察時所引發觀察學習當下以及事後之行為與壓力賀爾蒙的改變。在實驗一中，未有打鬥經驗的雄性觀察者，在三天觀察結束後立即或是一天後，於U形迷津內會快速的趨近並顯著地花較多時間去探索贏家示範者，顯示雄性觀察者比較有興趣與贏家示範者進行互動。相較於實驗一中使用了未有打鬥經驗之觀察者，在實驗二中則是使用了進行觀察學習前一天曾遭遇陌生攻擊者挫敗過一次的雄性觀察者，並發現這些觀察者在經歷連續三天觀察打鬥事件的當下以及後續在U形迷津中的立即和長期測試上，均會表現出與前一個實驗完全相反的行為模式（包含：較多的糞便排放、較多的逃跑與迴避、以及較少的探索時間），但此效果並不會出現在連續三天觀察中性事件之有挫敗經驗的觀察者上。這些結果顯示了挫敗經驗能有效地影響受挫倉鼠其後的行為表現。在實驗三中，使用了非侵入性的方法來偵測觀察者糞便內皮質醇代謝物（FCM）的含量。在實驗三A中，透過每3個小時蒐集一次糞便樣本的採樣方法，研究結果顯示在歷經一次攻擊互動後，輸家糞便內的皮質醇代謝物濃度於事件後的第三與第二十一小時會有明顯的上升，但這樣的改變並不會發生在贏家身上。在實驗三B中，則使用了依據實驗三A結果修改過的每18小時糞便採集法來分析實驗二中的觀察者所排放出的糞便樣本。在三天的觀察中，有挫敗經驗的雄性觀察者在觀察打鬥事件時，其排糞量有明顯的增加，但其糞便內皮質醇代謝物的濃度卻相對低於觀察中性互動事件的觀察者。同樣地在結束觀察後一天，面對贏家示範者表現激烈的觀察者身上也持續量測出糞便內皮質醇代謝物降低的情形。綜合以上所述，這些結果顯示了雄性倉鼠也能進行社會性訊息襲取，且個體過去社交挫敗的經驗會顯著地影響其後續遇到這些潛在對手時訊息的使用以及評估的方式。藉由觀察所獲得來的訊息，不只影響了生理上的恆定性，也影響著隨後的行為反應。

Observational learning, refers naïve individual acquires new behavior or information via observation of others’ doing, has been demonstrated in a variety of behaviors in different species. Gathering information from social interactions between others is termed eavesdropping which has been studied mainly in humans and certain kinds of fishes and birds, but not in other mammals. Using male golden hamsters and their agonistic behaviors, we developed a behavioral method to study eavesdropping. In this thesis, there are 3 experiments aiming at investigating consequential behavioral and hormonal changes in different groups of observers during and after the observation of two male demonstrators either fighting or encountering neutrally across a 3-day observational learning. In experiment 1, fighting naïve males approach quickly and spent significantly more time investigating the winning demonstrator in the U-maze immediately or one day after the 3-day observation indicating that they are more interested in interacting with the winners rather than the losers. In experiment 2, in contrast to those males in experiment 1, observers previously received one defeated experience from a novel fighter one day before the observational learning displayed completely opposite behavioral patterns (i.e., more defecation, more fleeing behavior and avoidance, and less investigation time toward the winning demonstrator) during the observation of the 3-day aggressive interactions and in the following immediate and long-term U-maze tests whereas such effects did not appear in the defeated males observed 3-day neutral interactions. These results indicate that the experience of social defeat can effectively influence subsequent behaviors in defeated hamsters. In experiment 3, a non-invasive method was applied to measure the levels of fecal cortisol metabolites (FCM). In experiment 3A, fecal samples were collected every 3 hours and our data indicate that a single fighting experience increased FCM level in the losers 3 hours and 21 hours after the aggressive encounter but has no effect on the winners at any time point. In experiment 3B, a modified 18-hour fecal collection procedure was adopted to analyze those fecal samples collected from observers in experiment 2. During the 3-day observation, these defeated males that observed aggressive interactions defecated more sequentially but their FCM level was relatively decreased compared to those that observed neutral encounters. One day after the last observation, the resultant decrease of FCM level was remained in those high responders that faced the winning demonstrators. Taken together, these results suggest that male hamsters eavesdrop too and the defeated experience significantly affects the ways they use the information and evaluate their potential opponents in subsequent encounter. The information gathered during the observation not only sufficiently affects physical homeostasis but also influences sequential behavioral responses.