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Male mammals respond to a risk of sperm competition conveyed by odours of conspecific males


Sperm competition occurs when a female copulates with two or more males and the sperm of those males compete within the female's reproductive tract to fertilize her eggs1,2. The frequent occurrence of sperm competition has forced males of many species to develop different strategies to overcome the sperm of competing males1,3. A prevalent strategy is for males to increase their sperm investment (total number of sperm allocated by a male to a particular female) after detecting a risk of sperm competition1,3,4. It has been shown that the proportion of sperm that one male contributes to the sperm pool of a female is correlated with the proportion of offspring sired by that male5,6. Therefore, by increasing his sperm investment a male may bias a potential sperm competition in his favour5,7,8. Here we show that male meadow voles, Microtus pennsylvanicus, increase their sperm investment when they mate in the presence of another male's odours. Such an increase in sperm investment does not occur by augmenting the frequency of ejaculations, but by increasing the amount of sperm in a similar number of ejaculations.

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Figure 1: Sperm investment in the RSC and the control context.
Figure 2: Sperm investment in relation to risk of sperm competition and male body weight.
Figure 3: Frequency of ejaculations in the control and the RSC contexts.


  1. Birkhead, T. R. & Møller, A. P. (eds) Sperm Competition and Sexual Selection (Academic, San Diego, 1998)

  2. Smith, R. L. (ed.) Sperm Competition and the Evolution of Animal Mating Systems (Academic, Orlando, 1984)

  3. Wedell, N., Gage, M. J. G. & Parker, G. A. Sperm competition, male prudence and sperm-limited females. Trends Ecol. Evol. 17, 313–320 (2002)

    Article  Google Scholar 

  4. Parker, G. A., Ball, M. A., Stockley, P. & Gage, M. J. G. Sperm competition games: a prospective analysis of risk assessment. Proc. R. Soc. Lond. B 264, 1793–1802 (1997)

    Article  ADS  CAS  Google Scholar 

  5. Dewsbury, D. A. in Sperm Competition and the Evolution of Animal Mating Systems (ed. Smith, R. L.) 547–571 (Academic, New York, 1984)

    Book  Google Scholar 

  6. Dziuk, P. J. Factors that influence the proportion of offspring sired by a male following heterospermic insemination. Anim. Reprod. Sci. 43, 65–88 (1996)

    Article  Google Scholar 

  7. Ginsberg, J. R. & Huck, U. W. Sperm competition in mammals. Trends Ecol. Evol. 4, 74–79 (1989)

    Article  CAS  Google Scholar 

  8. Schwagmeyer, P. L. & Foltz, D. W. Factors affecting the outcome of sperm competition in thirteen-lined ground squirrels. Anim. Behav. 39, 156–162 (1990)

    Article  Google Scholar 

  9. Wedell, N. & Cook, P. A. Butterflies tailor their ejaculate in response to sperm competition risk and intensity. Proc. R. Soc. Lond. B 266, 1033–1039 (1999)

    Article  Google Scholar 

  10. Gage, M. J. G. Risk of sperm competition directly affects ejaculate size in the Mediterranean fruit fly. Anim. Behav. 42, 1036–1037 (1991)

    Article  Google Scholar 

  11. Pilastro, A., Scaggiante, M. & Rasotto, M. B. Individual adjustment of sperm expenditure accords with sperm competition theory. Proc. Natl Acad. Sci. USA 99, 9913–9915 (2002)

    Article  ADS  CAS  Google Scholar 

  12. Pizzari, T., Cornwallis, C. K., Lovlie, H., Jakobsoon, S. & Birkhead, T. R. Sophisticated sperm allocation in male fowl. Nature 426, 70–74 (2003)

    Article  ADS  CAS  Google Scholar 

  13. Baker, R. R. & Bellis, M. A. Human Sperm Competition 203–227 (Chapman & Hall, New York, 1995)

    Google Scholar 

  14. Bellis, M. A., Baker, R. R. & Gage, M. J. G. Variation in rat ejaculates consistent with the Kamikaze-Sperm hypothesis. J. Mamm. 71, 479–480 (1990)

    Article  Google Scholar 

  15. Lezama, V., Orihuela, A. & Angulo, R. Sexual behavior and semen characteristics of rams exposed to their own semen or semen from a different ram on the vulva of the ewe. Appl. Anim. Behav. Sci. 75, 55–60 (2001)

    Article  Google Scholar 

  16. Dewsbury, D. A. Ejaculate cost and male choice. Am. Nat. 119, 601–610 (1982)

    Article  Google Scholar 

  17. Johnston, R. E. in Pheromones and Reproduction in Mammals (ed. Vandenbergh, J. G.) 3–37 (Academic, New York, 1983)

    Book  Google Scholar 

  18. Brown, R. E. & Macdonald, D. W. (eds) Social Odours in Mammals 1–36 (Oxford Univ. Press, Oxford, 1985)

  19. Ferkin, M. H. & Johnston, R. E. Meadow voles, Microtus pennsylvanicus, use multiple sources of scent for sex recognition. Anim. Behav. 49, 37–44 (1995)

    Article  Google Scholar 

  20. Boonstra, R., Xia, X. & Pavone, L. Mating system of the meadow vole, Microtus pennsylvanicus. Behav. Ecol. 4, 83–89 (1993)

    Article  Google Scholar 

  21. Dewsbury, D. A. Patterns of copulatory behavior in male mammals. Q. Rev. Biol. 47, 1–33 (1972)

    Article  CAS  Google Scholar 

  22. Dewsbury, D. A. Diversity and adaptation in rodent copulatory behavior. Science 190, 947–954 (1975)

    Article  ADS  CAS  Google Scholar 

  23. Gray, G. D. & Dewsbury, D. A. A quantitative description of the copulation behaviour of meadow voles (Microtus pennsylvanicus). Anim. Behav. 23, 261–267 (1975)

    Article  Google Scholar 

  24. Pound, N. Effects of morphine on electrically evoked contractions of the vas deferens in two congeneric rodent species differing in sperm competition intensity. Proc. R. Soc. Lond. B 266, 1755–1758 (1999)

    Article  CAS  Google Scholar 

  25. Parker, G. A. Sperm competition games: raffles and roles. Proc. R. Soc. Lond. B 242, 120–126 (1990)

    Article  ADS  Google Scholar 

  26. Birkhead, T. R. & Møller, A. P. Sperm Competition in Birds: Evolutionary Causes and Consequences (Academic, London, 1992)

    Google Scholar 

  27. Simmons, L. W. Sperm Competition and its Evolutionary Consequences in the Insects 144–187 (Princeton Univ. Press, Princeton, 2001)

    Google Scholar 

  28. Robb, G. W., Amann, R. P. & Killian, G. J. Daily sperm production and epididymal sperm reserves of pubertal and adult rats. J. Reprod. Fertil. 54, 103–107 (1978)

    Article  CAS  Google Scholar 

  29. Ferkin, M. H., Lee, D. N. & Leonard, S. T. The reproductive state of female voles affects their scent marking behavior and the responses of male conspecifics to such marks. Ethology 110, 257–272 (2004)

    Article  Google Scholar 

  30. Dewsbury, D. A. & Baumgardner, D. J. Studies of sperm competition in two species of muroid rodents. Behav. Ecol. Sociobiol. 9, 121–133 (1981)

    Article  Google Scholar 

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This work was supported by a Sigma Xi Grant-in-Aid of Research to J.d.-T., a NIH Grant to M.H.F. and a NIH Grant to the Tennessee Mouse Genome Consortium. J.d.-T. designed and carried out the experiments, analysed the data and wrote the paper; M.H.F. assisted in writing of the final drafts of the paper, as well as providing research facilities, animals and material.

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Correspondence to Javier delBarco-Trillo.

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delBarco-Trillo, J., Ferkin, M. Male mammals respond to a risk of sperm competition conveyed by odours of conspecific males. Nature 431, 446–449 (2004).

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