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Whether individuals respond consistently to winning and losing experiences
|Abstract:||動物為了競爭有限的資源而打鬥，許多因子會影響個體的打鬥行為，包括先前之獲勝/落敗經驗。打鬥的獲勝/落敗者在下一次的打鬥中往往展現出更強/更弱的攻擊性，且更容易獲勝/落敗(勝者效應/敗者效應)。許多物種都被發現會展現勝/敗者效應。此外，近期許多研究顯示，動物在不同環境刺激下的行為反應經常具有一致性(consistency)。然而，目前尚未有研究探討個體在得到獲勝或落敗經驗後的攻擊行為的改變程度是否具有一致性。本實驗以紅樹林鱂魚為研究物種，探討此議題。本研究先將實驗個體進行體長配對，並且兩兩對打以檢測打鬥能力，接著給予個體兩回合打鬥經驗(獲勝、落敗或控制經驗)後，檢測個體 (1)在兩回合的打鬥經驗後是否皆展現勝/敗者效應，以及 (2) 在兩回合打鬥經驗前後個體的攻擊性以及在獲得打鬥經驗後的攻擊性變化量是否具有一致性。在檢測(1)與(2)時並同時探討打鬥能力及荷爾蒙濃度對攻擊性與經驗效應展現的重要性。我先給予個體第一回合打鬥經驗(獲勝、落敗或是控制經驗)，並於經驗前後皆以鏡像測試量化個體之攻擊性(攻擊頻率、攻擊延遲時間)以測量攻擊性之改變。於一個月後再次給予個體另一回合相同打鬥或控制經驗(例如：先前獲得獲勝經驗，此次會隨機分配到獲勝經驗或控制經驗)，並再次測量攻擊性之改變。研究結果顯示 (1) 第一回合的經驗效應檢測中，個體攻擊頻率的改變量在打鬥能力較佳的個體中容易偵測到敗者效應、在皮質醇濃度較高的個體中容易偵測到勝者效應 ; 而個體攻擊延遲時間的改變量則顯示獲得落敗經驗的個體其攻擊延遲時間改變量會顯著比獲得獲勝經驗個體還要增長。第二回合的經驗效應檢測中，個體攻擊頻率的改變量並無偵測到任何的經驗效應 ; 而個體攻擊延遲時間的改變量則在打鬥能力較差的個體中容易偵測到勝者效應、在睪固酮濃度較高的個體中容易偵測到敗者效應。(2) 個體在不同階段所測量之攻擊性具正相關(有一致性)，兩回合皆獲得落敗經驗的個體其經驗後的攻擊頻率改變程度也具正相關(有一致性)，然而在兩回合經驗後展現出顯著勝/敗經驗效應之趨勢上則不具顯著相關性(缺乏一致性)。這些實驗結果顯示，打鬥能力與荷爾蒙濃度對於勝/敗者效應的展現有重要的影響，且個體不同階段的攻擊性具有一致性，然而個體展現勝/敗者效應之傾向則不具一致性。我在文內分別探討鏡像測試對勝/敗者效應展現的影響以及兩回合的經驗效應是否會加乘影響個體的攻擊性。此外也進一步討論勝敗經驗效應未展現一致性可能與前一次經驗效應未完全衰退或兩回合經驗的影響力不同有關。|
Animals often fight with each other to compete for limited resources. Many factors affect an individual’s fighting behaviors, including previous winning and/or losing experiences. Individuals with a recent winning/losing experience have a tendency to behave more/less aggressively and have a higher/lower probability to win a contest (winner effect/ loser effect). Winner and loser effects are reported for animals of all taxa. In addition, recent research has revealed that animals tend to behave consistently in response to different environmental stimuli. However, there has been no investigation into the consistency of the same individual’s responses to multiple winning/losing experiences. The mangrove killifish Kryptolebias marmoratus was used in this study. In this study, the fish were paired by their body length, and each paired individual would fight with each other to test their fighting ability. After that, I gave the fish two rounds of fighting experiences (winning, losing or control experiences), examining (1) whether individuals displayed winner or loser effects after both fighting experiences, and (2) whether individuals changed aggressiveness consistently after each round’s fighting experiences. The importance of fighting ability and hormone levels was also examined when testing (1) and (2). I used a mirror test to quantify each individual’s aggressiveness before and after their first-round experiences, and quantified the change in its aggressiveness after exposure to the fighting experience. After one month, individuals that had a winning or losing experience in the first round were exposed to the same experience or a control experience. They also had the same behavioral test. The results showed that (1) After the first round of contests, loser effects (represented by a reduction in attack frequency) were easier to detect in individuals with better fighting ability, and winner effects were easier to detect in individuals with higher cortisol levels; individuals’ latency to attack their mirror image also changed with experience effects. After the second round of contests, there was no significant change in individuals’ mirror attack frequency; tracking their latency to attack, it was easier to detect winner effects in the individuals with poor fighting ability, and loser effects in individuals with higher testosterone levels. (2) Individuals’ aggressiveness was positively correlated (consistent) between the different tests. The change in aggressiveness after the first and the second round of losing experiences were highly positively correlated. However, neither these individuals nor those with winning experiences consistently exhibited significant experience effects. The experimental results showed that fighting ability and hormone levels had an important impact on the winner/loser effects displayed. Individuals’ aggressiveness at different stages was consistent; however, the change in individuals’ aggressiveness after two similar fighting experiences was not. I subsequently discuss the impact of the mirror test on the display of winner/loser effects, and whether two rounds’ experiences reinforce their effect on an individual’s aggressiveness. In addition, I also discuss whether the fact that individuals did not respond consistently to winning or losing experiences was related to the still undiminished effect of the first experience or whether the impacts of the two rounds’ experiences were different.
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