社會經驗對打鬥能力與評估策略之重要性—以北美紅樹林鱂魚為例

Abstract

動物界中，個體的打鬥行為可能會受到其社會經驗的影響。本研究中之社會經驗是指和同種個體互動的經驗，包含自身參與之競爭互動（如相互威脅、展示、攻擊等）或是觀看其他個體間的競爭互動等。這些參與或觀看互動的經驗，可能有助於提升個體的打鬥技巧，進而提升其打鬥能力，並提高後續打鬥的獲勝機率。除此之外，社會經驗也可能會影響動物的打鬥評估策略。動物界中有很多物種被發現在打鬥時，其打鬥行為會受到自身或/和對手打鬥能力的影響。根據打鬥能力調整打鬥行為之策略稱為打鬥評估策略，而打鬥評估策略大致分為兩大類。如果個體是採取自我評估策略，其打鬥行為會受到自身打鬥能力的影響；如果個體是採取相互評估策略，其打鬥行為則會同時受到自身和對手打鬥能力的影響，也就是當個體採取相互評估策略時，其也會判斷對手的打鬥能力，進而影響其打鬥行為。個體是否能正確的判斷對手的打鬥能力，可能受到其社會經驗之影響。社會經驗往往有助於個體藉由對手的型態（如體型）與行為（如攻擊性）的特徵來判斷對手打鬥能力或判斷對手打鬥能力是否優於自己。例如，個體輸給或是曾經看過其他個體輸給體型較大的對手時，抑或是個體贏過或是曾經看過其他個體贏過體型較小的對手時，有助於個體了解體型與打鬥能力之間的關聯，並在後續打鬥時藉以評估對手的打鬥能力，進而影響其打鬥決策。本研究使用北美紅樹林鱂魚 (Kryptolebias marmoratus) 來探討社會經驗對打鬥行為的影響。K.marmoratus （1）具高攻擊性，且（2）先前的研究顯示有過打鬥經驗的個體，在同一場打鬥的不同階段會採取不同的打鬥評估策略（亦即在同一場打鬥中會同時採取到自我評估策略以及相互評估策略）。此外，（3）此魚之打鬥行為會受到先前打鬥經驗的影響，因此適合當作本研究之實驗對象。在本研究中，我將個體隨機分成無社會經驗組以及有社會經驗組（共兩組社會經驗處理）。無社會經驗組的個體在進行打鬥之前都不曾與其他個體互動；有社會經驗組的個體在進行打鬥之前則會和其他六隻個體互動過。首先，我讓無社會經驗的個體與有社會經驗的個體對打，來檢測社會經驗是否會影響個體的打鬥能力。接著，我讓具相同社會經驗處理的個體相互打鬥來檢測社會經驗是否會影響個體的打鬥評估策略。本研究結果發現，社會經驗不會影響 K.marmoratus 的打鬥能力或者打鬥評估策略。不管有無社會經驗，個體在進入到激烈打鬥前均採取相互評估策略，而一旦進入到激烈打鬥之後，則改採取自我評估策略。儘管如此，社會經驗卻影響了 K.marmoratus 的打鬥決策。有社會經驗之個體其打鬥未能於一小時內分出勝負的機率顯著較低，且在一小時內有分出勝負的打鬥中，打鬥持續時間較短（較快分出勝負）且打鬥激烈程度也較低。本研究顯示 K.marmoratus 不需社會經驗即可使用相互評估策略，且有過社會經驗之個體可以更有效率的解決一場打鬥，來節省打鬥時的能量消耗與時間成本。In the animal kingdom, an individual's fighting behavior may be influenced by its social experience. Social experience in this study refers to interactions with conspecifics, including participation in competitive activities such as mutual threats, displays, attacks etc., or observing competitive interactions among others. These interactive or observational experiences may help improve an individual's fighting skills, thereby enhancing its fighting ability, and increasing the likelihood of winning in subsequent fights. Moreover, social experience may also influence an animal's fighting assessment strategy. In the animal kingdom, many species have been found to adjust their fighting behaviors based on their own fighting ability and/or their opponent’s fighting ability. The strategies by which animals adjust their fighting behavior according to their fighting ability are referred to as fighting assessment strategies, which generally fall into two categories. If an individual adopts a self-assessment strategy, its fighting behavior is influenced by its own fighting ability. Conversely, if an individual adopts a mutual assessment strategy, its fighting behavior is influenced by both its own and its opponent's fighting abilities. This means that when adopting a mutual assessment strategy, an individual assesses the opponent's fighting ability, thereby affecting its own fighting behavior. The accuracy of an individual's assessment of its opponent's fighting ability may be influenced by its social experience. Social experience help individuals assess their opponent's fighting ability based on characteristics (such as body size) and behavioral traits (such as aggression), determining whether the opponent's fighting ability exceeds their own. For example, when an individual loses to or has observed others losing to larger opponents, or when an individual wins against or has observed others winning against smaller opponents, it helps the individual understand that larger body size may indicate better fighting ability. This study aims to investigate the impact of social experience on individual’s fighting behavior using the mangrove killifish (Kryptolebias marmoratus) as a model species. K. marmoratus is suitable for this study because (1) it exhibits high aggression, (2) previous research indicates that individuals with fighting experience adopt different fighting assessment strategies at different phases of a fight (adopting both self-assessment and mutual assessment strategies simultaneously), and (3) its fighting behavior is influenced by prior fighting experiences. In this study, individuals will be randomly assigned to either a group without social experience (where individuals have not encountered others before fighting) or a group with social experience (where individuals have interacted with six others before fighting). First, I staged contests between individuals without social experience and individuals with social experience to examine whether social experience affects individual’s fighting ability. Next, I staged contests between pairs of individuals without social experience and between pairs of individuals with social experience to determine if social experience influences individual’s fighting assessment strategies. The results of this study indicate that social experience does not affect the fighting ability or assessment strategy of K. marmoratus. Regardless of social experience, individuals adopt a mutual assessment strategy before engaging in escalated fights and switch to a self-assessment strategy once the fight escalates. However, social experience does impact the fighting decision in K. marmoratus. Individuals with social experience have a significantly lower likelihood of fighting unresolved within one hour. Moreover, in fights that are resolved within one hour, both the fighting duration and fighting intensity are lower than individuals without social experience. This study suggests that K. marmoratus can adopts a mutual assessment strategy without any social experience, and social experience allows individuals to reduce the costs associated with competitions for resources without affecting their ability to win.