PROMISCUITY DRIVES SEXUAL SELECTION IN A SOCIALLY MONOGAMOUS BIRD

Many socially monogamous species paradoxically show signs of strong sexual selection, suggesting cryptic sources of sexual competition among males. Darwin argued that sexual selection could operate in monogamous systems if breeding sex ratios are biased or if some males attract highly fecund females...

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Bibliographic Details
Published in:Evolution 2007-09, Vol.61 (9), p.2205-2211
Main Authors: Webster, Michael S, Tarvin, Keith A, Tuttle, Elaina M, Pruett-Jones, Stephen
Format: Article
Language:English
Subjects:
Animal reproduction
Animals
Aves
Bateman gradient
Birds
Breeding
Evolution
Evolutionary biology
extra-pair paternity
Female
Female animals
Male
Male animals
Malurus fairy-wrens
Malurus splendens
Mating behavior
monogamy
opportunity for selection
Original s
Ornithology
Predation
Reproduction
Reproductive success
Selection, Genetic
Sexual Behavior, Animal
Sexual selection
Songbirds - genetics
Statistical variance
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Summary:Many socially monogamous species paradoxically show signs of strong sexual selection, suggesting cryptic sources of sexual competition among males. Darwin argued that sexual selection could operate in monogamous systems if breeding sex ratios are biased or if some males attract highly fecund females. Alternatively, sexual selection might result from promiscuous copulations outside the pair bond, although several recent studies have cast doubt on this possibility, in particular by showing that variance in apparent male reproductive success (number of social young) differs little from variance in actual male reproductive success (number of young sired). Our results from a long-term study of the socially monogamous splendid fairy-wren (Malurus splendens) demonstrate that such comparisons are misleading and do not adequately assess the effects of extra-pair paternity (EPP). By partitioning the opportunity for selection and calculating Bateman gradients, we show that EPP has a strong effect on male annual and lifetime fitness, whereas other proposed mechanisms of sexual selection do not. Thus, EPP drives sexual selection in this, and possibly other, socially monogamous species.
ISSN:0014-3820
1558-5646
DOI:10.1111/j.1558-5646.2007.00208.x