Evolutionary Ecology

, Volume 11, Issue 5, pp 567–577 | Cite as

Sex ratios, local fitness enhancement and eusociality in the allodapine bee Exoneura richardsoni

  • Adam L. Cronin
  • Michael P. schwarz


Previous studies of a facultatively eusocial allodapine bee, Exoneura richardsoni Rayment, indicated that high levels of cooperative nesting among close relatives seem to be maintained by benefits that lead to increases in per capita brood production. These traits could lead to local fitness enhancement, which in turn could select for female-biased sex ratios. We show here that sex investment ratios in this species are female-biased in small colony sizes, becoming progressively male-biased in larger colonies, consistent with expectations for local fitness enhancement, but not explainable by alternative models. Our results support previous suggestions that local fitness enhancement can lead to sex ratio bias in primitively social Hymenoptera, but differ from previous studies by suggesting that patterns of bias could lower selective thresholds for sib-directed altruism in small colonies, but have an opposing effect in large colonies.


eusociality Exoneura local fitness enhancement sex allocation social evolution 


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Copyright information

© Chapman & Hall 1997

Authors and Affiliations

  • Adam L. Cronin
    • 1
  • Michael P. schwarz
    • 1
  1. 1.School of Biological SciencesFlinders University of South AustraliaAdelaideAustralia

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