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Open Access Research article

Baculum morphology predicts reproductive success of male house mice under sexual selection

Paula Stockley1*, Steven A Ramm12, Amy L Sherborne34, Michael D F Thom15, Steve Paterson3 and Jane L Hurst1

Author affiliations

1 Mammalian Behaviour & Evolution Group, Department of Evolution, Ecology and Behaviour, University of Liverpool, Leahurst Campus, Chester High Road, Neston CH64 7TE, UK

2 Department of Evolutionary Biology, Bielefeld University, Morgenbreede 45, Bielefeld 33615, Germany

3 Department of Evolution, Ecology and Behaviour, University of Liverpool, Crown Street, Liverpool L69 7ZB, UK

4 Section of Cancer Genetics, Institute of Cancer Research, Cotswold Road, Sutton, Surrey SM2 5NG, UK

5 Department of Biology, University of York, Wentworth Way, Heslington, York Y010 5DD, UK

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Citation and License

BMC Biology 2013, 11:66  doi:10.1186/1741-7007-11-66

Published: 26 June 2013



Diversity in penile morphology is characterised by extraordinary variation in the size and shape of the baculum (penis bone) found in many mammals. Although functionally enigmatic, diversity in baculum form is hypothesised to result from sexual selection. According to this hypothesis, the baculum should influence the outcome of reproductive competition among males within promiscuous mating systems. However, a test of this key prediction is currently lacking.


Here we show that baculum size explains significant variation in the reproductive success of male house mice under competitive conditions. After controlling for body size and other reproductive traits, the width (but not length) of the house mouse baculum predicts both the mean number of offspring sired per litter and total number of offspring sired.


By providing the first evidence linking baculum morphology to male reproductive success, our results support the hypothesis that evolutionary diversity in baculum form is driven by sexual selection.

Baculum; Cryptic female choice; Genital evolution; Os penis; Penile morphology; Postcopulatory sexual selection; Sperm competition