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About the Cover


A male long-tailed manakin. In this species alpha and beta males cooperate in dual-mate courtship displays, but only the alpha partner mates during the partnership, which may last for several years. Long-term field data and genetic analysis of relatedness were used to exclude the two leading explanations for such cooperation—kin selection and reciprocity. Instead, the cooperation is a form of mutualism, with direct but long-delayed benefits to the nonmating beta males. See page 1030. [Photo: Richard LaVal]


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Science. ISSN 0036-8075 (print), 1095-9203 (online)