Evolutionary stability of egg trading and parceling in simultaneous hermaphrodites: The chalk bass revisited

Philip H. Crowley, Mary K. Hart

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


Several species of simultaneously hermaphroditic seabasses living on coral reefs mate by alternating male and female roles with a partner. This is known as egg trading, one of the classic and most widely cited examples of social reciprocity among animals. Some of the egg-trading seabass species, including the chalk bass, Serranus tortugarum, switch mating roles repeatedly, having subdivided their clutch of eggs into parcels offered to the partner for fertilization. Here we attempt to understand these dynamics as a pair of evolutionary games, modifying some previous approaches to better reflect the biological system. We find that the trading of egg clutches is evolutionarily stable via byproduct mutualism and resistant to invasion by rare individuals that take the male role exclusively. We note why and how parceling may reflect sexual conflict between individuals in the mating pair. We estimate evolutionarily stable parcel numbers and show how they depend on parameter values. Typically, two or more sequential parcel numbers are evolutionarily stable, though the lowest of these yields the highest fitness. Assuming that parcel numbers are adjusted to local conditions, we predict that parcel numbers in nature are inversely related both to mating group density (except at low density) and predation risk.

Original languageEnglish
Pages (from-to)420-429
Number of pages10
JournalJournal of Theoretical Biology
Issue number3
StatePublished - Jun 7 2007

Bibliographical note

Funding Information:
We thank Craig Sargent, Chuck Fox, David Westneat, members of the Crowley Lab and the UK Evolutionary Ecology Group for discussions of these and closely related ideas. We especially appreciate comments and suggestions on the manuscript from Derik Castillo Guajardo, Eric Fischer, Gisela García-Ramos, Cristina Lorenzi, Yoriko Saeki, Gabriella Sella, Kausalya Shenoy, Dave Westneat, and two anonymous reviewers. Special thanks go to the reviewers who pointed out the alternative version of inequality (1) and the likelihood that the magnitudes of α and β in Eq. (1) vary with the frequency of cooperative behavior. MKH acknowledges the UK Graduate School and Biology Graduate Program for Fellowship support and grants from the UK Biology Department's Gertrude Flora Ribble Fund, the UK Association of Emeriti Faculty, the Smithsonian Tropical Research Institute, the PADI Foundation, and Sigma Xi.


  • Evolution of cooperation
  • Evolutionary game theory
  • Mating system theory
  • Reciprocal altruism
  • Serranidae
  • Serranus tortugarum
  • Sexual conflict

ASJC Scopus subject areas

  • Statistics and Probability
  • Modeling and Simulation
  • Biochemistry, Genetics and Molecular Biology (all)
  • Immunology and Microbiology (all)
  • Agricultural and Biological Sciences (all)
  • Applied Mathematics


Dive into the research topics of 'Evolutionary stability of egg trading and parceling in simultaneous hermaphrodites: The chalk bass revisited'. Together they form a unique fingerprint.

Cite this