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Sophisticated sperm allocation in male fowl


When a female is sexually promiscuous, the ejaculates of different males compete for the fertilization of her eggs1; the more sperm a male inseminates into a female, the more likely he is to fertilize her eggs2. Because sperm production is limited and costly, theory predicts that males will strategically allocate sperm (1) according to female promiscuity1,3,4,5, (2) saving some for copulations with new females3,6,7, and (3) to females producing more and/or better offspring3,8. Whether males allocate sperm in all of these ways is not known, particularly in birds where the collection of natural ejaculates only recently became possible. Here we demonstrate male sperm allocation of unprecedented sophistication in the fowl Gallus gallus. Males show status-dependent sperm investment in females according to the level of female promiscuity; they progressively reduce sperm investment in a particular female but, on encountering a new female, instantaneously increase their sperm investment; and they preferentially allocate sperm to females with large sexual ornaments signalling superior maternal investment. Our results indicate that female promiscuity leads to the evolution of sophisticated male sexual behaviour.

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Figure 1: Differential sperm allocation and female promiscuity.
Figure 2: Preferential sperm investment in new females.
Figure 3: Preferential sperm investment in new females (continued).
Figure 4: Mate choice and strategic sperm allocation by male fowl.


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We thank A. Donald for help with sperm counting, and A. MacColl for statistical advice. T.P. was supported by a scholarship from the Swedish University of Agricultural Sciences and a grant from the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS); T.R.B. by a grant from the Natural Research Council (NERC); C.K.C. by a studentship from NERC (to T.R.B.); and H.L. by a studentship from the Zoology Department of Stockholm University. T.R.B. and T.P. developed the sperm collection technique; T.P. designed the female promiscuity and female novelty experiments, and together with C.K.C. and H.L. carried them out; C.K.C. designed the female quality experiment with T.R.B. and carried it out together with H.L.; C.K.C. analysed the data with T.P.; T.P. wrote the paper; S.J. helped with field work and the provision of research facilities.

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Correspondence to Tommaso Pizzari.

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Pizzari, T., Cornwallis, C., Løvlie, H. et al. Sophisticated sperm allocation in male fowl. Nature 426, 70–74 (2003).

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