Dynamic Games and Applications

, Volume 4, Issue 4, pp 379–390 | Cite as

The Economics of Egg Trading: Mating Rate, Sperm Competition and Positive Frequency-Dependence

  • Jonathan M. Henshaw
  • Michael D. Jennions
  • Hanna Kokko


Egg trading—the alternating exchange of egg parcels during mating by simultaneous hermaphrodites—is one of the best-documented examples of reciprocity between non-relatives. By offering eggs only to partners who reciprocate, traders increase their reproductive success in the male role, but at a potential cost of delaying or reducing fertilisation of their own eggs. Although several authors have considered the evolutionary stability of egg trading once it has evolved, little attention has been paid to how egg trading can invade a population in the first place. We begin to tackle this problem by formally showing that egg trading is under positive frequency-dependent selection: once the proportion of traders in a population exceeds a certain threshold, egg trading will go to fixation. We show that if mate encounters occur frequently, then the cost of withholding eggs from unreciprocating partners is reduced, making it easier for egg trading to evolve. In contrast, the presence of opportunistic ‘streaking’, where unpaired individuals join mating pairs but contribute only sperm, makes it more difficult for egg trading to invade. This is because streakers weaken the link between the number of eggs an individual can offer and its male-role reproductive success.


Altruism Cooperation Direct reciprocity Mate choice Assortative mating 



We would like to thank two anonymous reviewers for their thoughtful comments and criticisms. Funding was provided by the Australian Research Council and an Australian Postgraduate Award.

Supplementary material

13235_2014_107_MOESM1_ESM.pdf (98 kb)
Supplementary material 1 (pdf 98 KB)


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Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  • Jonathan M. Henshaw
    • 1
  • Michael D. Jennions
    • 1
  • Hanna Kokko
    • 1
  1. 1.Research School of BiologyThe Australian National UniversityCanberraAustralia

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