新、舊打鬥經驗是否會改變彼此對後續打鬥行為的影響

Abstract

近期打鬥的勝負結果會影響到個體後續的打鬥行為：有過獲勝/落敗經驗的個體，再次遇到競爭對手時，其攻擊性及打鬥獲勝機率往往會提高/降低（勝者/敗者效應）。打鬥經驗對個體的影響力可能隨著時間的過去或是因為獲得其他打鬥經驗而改變。打鬥經驗的影響力隨著時間的過去而衰退在許多的研究中都有發現；然而，雖然在野外動物可能短時間內經歷多次的打鬥，卻很少有研究去探討不同的打鬥經驗是否會改變彼此的影響力，而影響到不同經驗間效應的整合。本研究藉由給予紅樹林鱂魚Kryptolebias marmoratus兩次打鬥經驗（在打鬥測試的前兩天與前一天各給予一次打鬥經驗），檢測此兩次經驗是否會互相影響彼此的效應，如果經驗間會互相作用，則兩次經驗之效應的總和會高於或低於累加總和；如果經驗間不會互相作用，則兩次經驗以簡單的累加方式影響個體後續的打鬥行為。由於此魚的經驗效應會受到一個月前勝敗結果的影響，因此實驗時將最近一次打鬥（一個月前）之獲勝和落敗的個體分開測試；同一打鬥配對的個體具有相同之一個月前的勝敗結果（勝者或敗者配對）。結果顯示（1）不論是勝者或敗者配對，個體的打鬥行為明顯的受到兩天前落敗經驗的影響，表現出敗者效應；而兩天前之獲勝經驗所造成之勝者效應則幾乎偵測不到；（2）一個月前的勝敗結果會影響到近期兩次打鬥經驗的整合：敗者配對之個體，若連續獲得兩次獲勝經驗，其率先鰓蓋展示的機率會高於簡單累加效應的預期值，顯示此連續兩次的獲勝經驗所造成的效應總和高於兩個經驗之個別效應的加總；而勝者配對之個體，若連續獲得兩次落敗經驗，其率先鰓蓋展示、率先攻擊和獲勝機率皆低於簡單累加效應的預期值，表示連續兩次的落敗經驗所造成的效應總和高於兩個經驗之個別效應的加總。由本研究得知，連續兩次打鬥經驗之效應的整合不都只是簡單地累加其影響力，連續兩次的獲勝或落敗經驗可能會互相作用增強彼此的影響力。The outcomes of recent contests are known to influence an individual’s behavior in subsequent contests: a winning/losing experience increases/decreases an individual’s aggressiveness and probability of winning a subsequent contest（winner/loser effect）. Animals in the field are likely to have frequent contest encounters, but how these multiple experiences combine to influence an individual’s subsequent contest behavior is rarely explored. In this study, I gave individuals of Kryptolebias marmoratus, a mangrove killifish, two contest experiences（2 days and 1 day prior to a staged contest）to examine whether the effects of these two experiences were additive or whether the effect of one experience was changed by interaction with the other. Because contest decision in this fish is influenced by experience acquired as long as one month previously, individuals that had won their last contest（about one month before this study） were paired up among themselves, as were those that had lost, and tested separately as winner and loser pairs. The results showed that a losing experience received two days previously significantly influenced fighting behavior in contests staged and caused detectable loser effects in both winner and loser pairs. A winning experience received two days previously, on the other hand, had no significant effect on the fighting behavior in contests. More interestingly, the results also showed that the way in which the two recent contest experiences combined depended on the outcome of the contest that the fish participated in one month before this study. In loser pairs, two recent consecutive winning experiences increased an individual’s probability of initiating gill displays more than if the effects of the two experiences had been additive. By contrast, in winner pairs, two consecutive losing experiences reduced an individual’s probability of initiating gill displays, initiating attacks and winning more than if the effects of the two experiences had been additive. This result may indicate that two consecutive winning or losing experiences enhance each other such that their combined effect is more than the additive.