Maintenance of sperm variation in a highly promiscuous wild bird

Calhim, S., Double, M.C., Margraf, N., Birkhead, T.R. and Cockburn, A. (2011) Maintenance of sperm variation in a highly promiscuous wild bird. PloS One , 6 (12). Art no. e28809. ISSN 1932-6203

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Abstract

Postcopulatory sexual selection is an important force in the evolution of reproductive traits, including sperm morphology. In birds, sperm morphology is known to be highly heritable and largely condition-independent. Theory predicts, and recent comparative work corroborates, that strong selection in such traits reduces intraspecific phenotypic variation. Here we show that some variation can be maintained despite extreme promiscuity, as a result of opposing, copulation-role-specific selection forces. After controlling for known correlates of siring success in the superb fairy-wren (Malurus cyaneus), we found that (a) lifetime extra-pair paternity success was associated with sperm with a shorter flagellum and relatively large head, and (b) males whose sperm had a longer flagellum and a relatively smaller head achieved higher within-pair paternity. In this species extrapair copulations occur in the same morning, but preceding, pair copulations during a female's fertile period, suggesting that shorter and relatively larger-headed sperm are most successful in securing storage (defense), whereas the opposite phenotype might be better at outcompeting stored sperm (offense). Furthermore, since cuckolding ability is a major contributor to differential male reproductive output, stronger selection on defense sperm competition traits might explain the short sperm of malurids relative to other promiscuous passerines.

Item Type:	Article
Copyright, Publisher and Additional Information:	© 2011 Calhim et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Keywords:	Superb Fairy-Wrens; Postcopulatory Sexual Selection; Malurus-Cyaneus; Extra-Pair; Competition Games; Passerine Birds; Fertilization Success; Reproductive Success; Lepomis-Macrochirus; Gallus-Domesticus
Academic Units:	The University of Sheffield > Faculty of Science (Sheffield) > School of Biological Sciences (Sheffield) > Department of Animal and Plant Sciences (Sheffield)
Depositing User:	Miss Anthea Tucker
Date Deposited:	27 Jan 2012 10:57
Last Modified:	08 Feb 2013 17:36
Published Version:	http://dx.doi.org/10.1371/journal.pone.0028809
Status:	Published
Publisher:	Public Library Science
Refereed:	Yes
Identification Number:	10.1371/journal.pone.0028809
URI:	http://eprints.whiterose.ac.uk/id/eprint/43680

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