COOPERATIVE DISPLAY AND RELATEDNESS AMONG MALES IN A LEK-MATING BIRD

Long-tailed manakins mate in leks and cooperate in multiyear male-male partnerships. An alpha male is responsible for virtually all mating, whereas a beta male assists in the courtship displays. Such altruism b y the beta male poses a problem for evolutionary theory because most t heoretical treatments and empirical examples of cooperative behavior i nvolve kin selection or reciprocity. Here it is shown that alpha and b eta partners are not relatives and that reciprocity is not involved. I nstead, direct, though long-delayed benefits to beta males are demonst rated, which include rare copulations, ascension to alpha status, and female lek fidelity. These benefits maintain this unusual form of male -male cooperation.