Ownership, size and reproductive status affect the outcome of food ball contests in a dung roller beetle: when do enemies share?
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Theory predicts that asymmetry between contenders influences their ability to defend resources. More recently, some theoretical approaches have also examined the circumstances that might promote sharing of the disputed resources. We tested these hypotheses in males of the ball roller beetle Canthon cyanellus cyanellus. Males fight for possession of a food ball, which is a vital resource used for nesting. We evaluated the role of food resource ownership, body size and reproductive status on the outcome of contests (win, lose or share) between males that rolled a food ball (owners or finders) either alone or with a female partner, when faced with male intruders (or joiners). Large owners of a food ball had a higher probability of victory than small intruders, and small owners had a high probability of losing when faced with large intruders. The reproductive status of both contenders also influenced their chances of winning: previously mated owners of a food ball had a higher probability of winning than virgin owners. Males of a similar size tended to split the food ball, thereby sharing the resource. Our results suggest that competitors may adjust the intensity of their aggression depending at least on their own resource holding power (RHP), the value of the resource in dispute and perhaps even the RHP of their opponents. Sharing the food ball emerges as a fresh solution between similarly matched contestants.
KeywordsAsymmetric contests Canthon cyanellus cyanellus Foraging competition Resource holding power Food sharing Roller beetles
We thank Roberto Munguía and Roger Guevara for statistical advice. Keith MacMillan translated and revised a first English version of the manuscript. Comments by two anonymous reviewers greatly improved the manuscript. Bianca Delfosse revised the final version of the manuscript. This work was supported by CONACYT-Mexico (49472-Q). IACF is grateful to CONACyT for a graduate studies scholarship (number 124849).
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