By Jason V. Watters
Animal Behaviour, Volume 70, Issue 5, November 2005, Pages 1055-1062, ISSN 0003-3472, DOI: 10.1016/j.anbehav.2005.01.025.

Females often prefer to mate with males with certain traits. Preferred males might cooperate with females to reduce the direct costs of reproduction. However, unpreferred males use alternative tactics that attempt to alter female choice in their favour, such as coercion. When this occurs, females have to choose whether to pay the costs of coercion and mate with preferred males or avoid the costs of coercion by mating with unpreferred males. The decisions females make are expected to depend on the relative costs and benefits of mating with preferred and unpreferred males and the frequencies of the two male types. Here I present a study of simultaneous coercion and cooperation among wild coho salmon, Oncorhynchus kisutch. This species is well known for its alternative male types, sneakers and fighters. I found evidence that females prefer to mate with, and cooperate with, small sneaker males, but regularly mate with large fighting males to avoid the costs of coercion. Large males were more aggressive towards females than were small males. In addition, females spent more time preparing their nests when they were alone with small males than when they were accompanied by large males, and they oviposited for longer durations when small males were part of the spawning group.

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