體型差異與近期勝敗經驗如何共同影響動物的打鬥決策

How do recent contest experience and differences in body size jointly influence contest decisions

陳昱儒(Yu-Ju Chen)

指導教授 ： 許鈺鸚

國立臺灣師範大學/理學院/生命科學研究所/碩士(2013年)

摘要

動物的攻擊性和打鬥獲勝機率經常受到自身狀況的影響，例如體型越大的個體，其攻擊性與獲勝機率往往越高。另外，近期打鬥的獲勝/落敗結果也會提升/降低個體的攻擊性，進而提升/降低其獲勝機率(勝者/敗者效應)。由於動物的打鬥行為表現應該會同時受到各個因子的影響，因此，本研究之目的為瞭解體型與近期勝敗經驗如何共同影響動物的打鬥決策，以及此二因子分別是對哪些行為造成影響，進而影響打鬥結果。本研究使用3×4之二因子實驗設計(共12種處理)，包含三種體型差距處理(體長0~1公厘差異、1~2公厘差異及2~3公厘差異)以及四種經驗差異處理(打鬥者雙方皆無近期勝敗經驗；較大個體無經驗，較小個體具獲勝經驗；較大個體具落敗經驗，較小個體無經驗；較大個體具落敗經驗，較小個體具獲勝經驗)，並以Kryptolebias marmoratus，一種紅樹林鱂魚為實驗動物。實驗結果顯示：(1)體型與勝敗經驗影響不同激烈程度打鬥之結果，打鬥經驗影響低激烈程度打鬥(無纏鬥)的勝敗結果，體型則影響高激烈程度打鬥(纏鬥)之勝敗結果；(2)當打鬥雙方皆無近期打鬥經驗時，體長較大的個體之獲勝機率顯著較高；(3)當打鬥雙方體長差異為0~1公厘時，有落敗經驗個體之獲勝機率顯著低於具獲勝經驗的對手；(4)體型與打鬥經驗以累加方式影響動物的打鬥結果：當具落敗經驗個體與體型相當或較自己小1~2公厘的無經驗對手打鬥時，其獲勝機率有低於0.5之趨勢，但若其體型較對手來的大(2~3公厘)時，其獲勝機率則可提升至0.5，顯示落敗經驗對此魚打鬥時所造成的負面影響，可以被2~3公厘之體長優勢所彌補。總結而言，體型與打鬥經驗皆會影響K. marmoratus之打鬥行為，且此二者之影響具累加性。此外，體型與打鬥經驗分別影響高、低激烈程度打鬥之結果，可能是因為體型影響個體之實際打鬥能力，而打鬥經驗雖然影響個體之打鬥意願卻並未改變個體之實際打鬥能力，因此一旦打鬥雙方皆有較高之打鬥意願而進入互相纏鬥階段時，打鬥經驗對勝負結果的影響減弱，體型大小反而成為重要的影響因子。

關鍵字

打鬥行為 ； 體型 ； 勝者效應 ； 敗者效應 ； Kryptolebias marmoratus

並列摘要

Animals’ performance in contest is influenced by differences in the contestants’ intrinsic strengths. For example, individuals with a larger weapon or body size are more likely to win than their opponents. Animals’ aggressiveness and winning probabilities are also known to be increased / decreased by winning / losing a recent contest (winner / loser effect). In practice, many different factors may influence contest behaviors at the same time. I investigated how body-size difference and recent contest experience jointly influence contest decisions. Pairs of Kryptolebias marmoratus were divided into three size-difference treatments (Δ, in mm 0<Δ≤1, 1<Δ≤2, 2<Δ≤3) and four treatments with different combinations of recent contest experience: i. both fish no experience; ii. larger fish no experience / smaller fish winning experience; iii. larger fish losing experience / smaller fish no experience or; iv. larger fish losing experience / smaller fish winning experience), a total of 12 (3×4) treatments. The results showed that: (1) Although contest experience influenced an individual’s probability of winning in less intense (non-escalated) fights, body size had an important influence on the outcome of more intense (escalated) fights, whereas contest experience did not; (2) when both the contestants had no recent contest experience, the larger opponent was more likely to win; (3) when the size difference was small (≤1 mm), individuals with a winning contest experience were significantly more likely to win than opponents with a losing experience; (4) size difference and contest experience jointly influence individuals’ contest decisions, a size advantage 2-3 mm compensates for the disadvantage caused by losing experience in likelihood of winning contests. These results could indicate that contest experience modifies an individual’s willingness to fight but does not change its actual fighting ability. When contests are resolved without escalating into physical fights, individuals with better contest experience persist longer before retreating and have a higher chance of winning. But once contests do escalate into physical fights, actual fighting ability (positively correlated with body size) is more important in determining contest outcome than contest experience. Overall, this study shows that body size and contest experience jointly influence contest outcome, but the two factors come into play in contests of different intensities.

並列關鍵字

contest behavior ； body size ； winner effect ； loser effect

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