Male reproductive suppression in the cooperatively breeding fish Neolamprologus pulcher |
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Authors: | Fitzpatrick, J.L. Desjardins, J.K. Stiver, K.A. Montgomerie, R. Balshine, S. |
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Affiliation: | a Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada, b Animal Behaviour Group, Department of Psychology, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada, and c Department of Biology, Queen's University, Kingston, Ontario K7L 3N6, Canada |
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Abstract: | In most cooperative breeders, dominants suppress the reproductionof subordinates. However, two previous studies of Neolamprologuspulcher, a cooperatively breeding cichlid fish, have suggestedthat socially subordinate helper males sneak fertilizationsfrom dominant breeding males. If such sneaking does occur, boththeoretical work and empirical studies of other fish speciessuggest that sperm competition will select for increased reproductiveinvestment by sneaker males, relative to more dominant males.To address these issues, we quantified gonadal investment andsperm characteristics of 41 N. pulcher male breeders and 62male helpers from 55 groups in Lake Tanganyika. Gonadal investmentfollowed patterns consistent with reproductive suppression,with breeders having considerably larger testes masses thanhelpers. Breeders also had faster and longer swimming spermand a higher percentage of motile sperm compared to helpers.However, sperm characteristics of large helpers were similarto those of breeders, but these same helpers had lower testesmasses. Thus, large helpers had sperm that were physiologicallyequivalent to that of breeders, but their relatively small gonadsimply that they were reproductively suppressed. |
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Keywords: | Cichlidae dominance hierarchies Lake Tanganyika reproductive physiology social status sperm competition. |
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