Contest experience and body size affect different types of contest decisions
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This study examined the relative importance of contest experience and size differences to behavioral decisions over the course of contests. Using a mangrove rivulus fish, Kryptolebias marmoratus, we showed that although contest experience and size differences jointly determined contest outcomes, they affected contestants’ interactions at different stages of contests. Contest experience affected behavioral decisions at earlier stages of contests, including the tendency and latency to launch attacks, the tendency to escalate contests into mutual attacks and the outcome of non-escalated contests. Once contests were escalated into mutual attacks, the degree of size difference affected the fish’s persistence in escalation and chance of winning, but contest experience did not. These results support the hypothesis that contest experience modifies individuals’ estimation of their fighting ability rather than their actual strength. Furthermore, (1) in contests between two naïve contestants, more than 60 % of fish that were 2–3 mm smaller than their opponent escalated the contest to physical fights, even though their larger opponents eventually won 92 % of escalated fights and (2) fish with a losing experience were very likely to retreat in the face of an opponent 2–3 mm smaller than them without escalating. The result that a 2–3 mm size advantage could not offset the influence of a losing experience on the tendency to escalate suggests that, as well as depending on body size, the fish’s physical strength is influenced by other factors which require further investigation.
KeywordsAnimal contest Behavioral decisions Winner–loser effect Size difference Kryptolebias marmoratus
We thank the editor and two anonymous reviewers for helpful suggestions on improving the manuscript. We also thank Yu-Ting Chang for transcribing behavioral data from the video recordings and Alan Watson for help with comments and on the manuscript. We thank Yi-Ting Lan for providing us a photograph of K. marmoratus. This research was supported by Taiwan National Science Council (NSC100-2621-B-003-005-MY3).
Compliance with ethical standards
Conflict of interest
The authors assert that they have no conflicts of interest.
The Animal Care and Use Committee of National Taiwan Normal University approved K. marmoratus as the study organism and the procedures for the use of the fish (permit #99034). To measure a fish’s SL, we moved the fish from its maintenance container to a clear plastic bag where it could be measured and kept moist with a hand net. We measured the fish through the bag with a digital caliper and then returned the fish to its maintenance container. To mark the fish, we netted the fish and placed it inside folded plastic wrap to keep it moist. We exposed the tail and dragged a needle over the non-vascularized thin membrane between two of the caudal fin rays to break it. All fish resumed regular feeding behavior within 5 s of marking, which did not cause bleeding or observable adverse effects upon the fishes’ health or behavior (Hsu et al. 2008). The membrane usually grows back completely in 3 d. All contests were videotaped and monitored by an observer sitting behind the camcorder. Contests were terminated 5 min after one of the contestants retreated from its opponent’s displays/attacks. This time period was used to confirm the winner–loser status of a contest pair. During this period, the loser was able to flip out of water and stick to the side of the aquarium to avoid post-contest harassment from the winner. All fish were visually inspected, returned to their maintenance containers and fed brine shrimp (Artemia) nauplii after the contests. None of the fish suffered visible physical injury (e.g., scale loss, wounds, bleeding, abnormal swimming behavior) from the contests.
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