Search tips
Search criteria 


Logo of procbThe Royal Society PublishingProceedings BAboutBrowse by SubjectAlertsFree Trial
Proc Biol Sci. 1997 December 22; 264(1389): 1793–1802.
PMCID: PMC1688741

Sperm competition games: a prospective analysis of risk assessment.


We develop the logic of assessment of sperm competition risk by individual males where the mechanism of sperm competition follows a 'loaded raffle' (first and second inseminates of a female have unequal prospects). Male roles (first or second to mate) are determined randomly. In model 1, males have no information about the risk associated with individual females and ejaculation strategy depends only on the probability, q, that females mate twice. Evolutionarily stable strategy (ESS) ejaculate expenditure increases linearly from zero with q, and reduces with increasing inequality between ejaculates, though the direction of the loading (which role is favoured) is unimportant. In model 2, males have perfect information and can identify each of three risk states: females that will (1) mate just once ('no risk'), (2) mate twice but have not yet mated ('future risk'), and (3) mate twice and have already mated ('past risk'). The ESS is to ejaculate minimally with 'no risk' females, and to expand equally with 'past' and 'future' risk females; the direction of the competitive loading is again unimportant. Expenditure again increases with risk, but is now non-zero at extremely low risk. Model 3 examines three cases of partial information where males can identify only one of the three risk states and cannot distinguish between the other two: they therefore have just two information sets or 'contexts'. Expenditure in both contexts typically rises non-linearly from zero with q, but (whatever the loading direction) expenditure is higher in the context with higher risk (e.g. if contexts are 'mated' and 'virgin', males spend more with mated females). However, in highly loaded raffles, sperm expenditure can decrease over part of the range of risk. Also, the direction of the loading now affects expenditure. Biological evidence for the predictions of the models is summarized and discussed.

Full Text

The Full Text of this article is available as a PDF (317K).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.
  • Ball MA, Parker GA. Sperm competition games: external fertilization and "adaptive"' infertility. J Theor Biol. 1996 May 21;180(2):141–150. [PubMed]
  • Ball MA, Parker GA. Sperm competition games: inter- and intra-species results of a continuous external fertilization model. J Theor Biol. 1997 Jun 21;186(4):459–466. [PubMed]
  • Harcourt AH, Harvey PH, Larson SG, Short RV. Testis weight, body weight and breeding system in primates. Nature. 1981 Sep 3;293(5827):55–57. [PubMed]
  • Hosken DJ. Sperm competition in bats. Proc Biol Sci. 1997 Mar 22;264(1380):385–392. [PMC free article] [PubMed]
  • Parker GA. Why are there so many tiny sperm? Sperm competition and the maintenance of two sexes. J Theor Biol. 1982 May 21;96(2):281–294. [PubMed]
  • Parker GA. Sperm competition games: sperm size and sperm number under adult control. Proc Biol Sci. 1993 Sep 22;253(1338):245–254. [PubMed]
  • Parker GA, Begon ME. Sperm competition games: sperm size and number under gametic control. Proc Biol Sci. 1993 Sep 22;253(1338):255–262. [PubMed]
  • Warner RR, Shapiro DY, Marcanato A, Petersen CW. Sexual conflict: males with highest mating success convey the lowest fertilization benefits to females. Proc Biol Sci. 1995 Nov 22;262(1364):135–139. [PubMed]
  • Zeh JA, Zeh DW. The evolution of polyandry II: post-copulatory defenses against genetic incompatibility. Proc Biol Sci. 1997 Jan 22;264(1378):69–75. [PMC free article]

Articles from Proceedings of the Royal Society B: Biological Sciences are provided here courtesy of The Royal Society