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Waders for sex

Sexual dimorphism in size is common in birds.

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Males are usually larger than females, although in some taxa reversed size dimorphism RSD predominates. Whilst direct dimorphism is attributed to sexual selection in males giving greater reproductive access to females, the evolutionary causes of RSD are still unclear.

Four different hypotheses could explain the evolution of RSD in for birds: It is based on waders assumption that small male size facilitates food acquisition in terrestrial habitats where chick rearing takes place and that larger females can accumulate more reserves for egg laying in coastal sites.

I tested these hypotheses in monogamous waders using several comparative methods.

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Given the current knowledge of the phylogeny of waders group, the evolutionary history of waders seems only compatible with the hypothesis that RSD has evolved as an adaptation for increasing display performance in males. Xxx mobile species with acrobatic displays males also had a higher aspect ratio than females although no sexual difference was found in non-acrobatic species.

These results suggest that acrobatic flight displays could have produced changes in the morphology of some species and suggest the existence of selection favouring sex manoeuvrability in species with acrobatic flight displays. Oxford Sex Press is a department of the University of Oxford.