A Test of Two Skew Models to Explain Cooperative Breeding

  • Deby L. Cassill
  • Indira Kuriachan
  • S. Bradleigh Vinson


Two competing models, reproductive skew and skew selection, have been constructed to explain the evolution of cooperation among unrelated breeders. Reproductive skew is a trade-off model that assumes breeding occurs under scarce resource conditions. One breeder gains units of fecundity at the expense of other breeders during aggressive, altruistic or tug-of-war transactions. After joining, the distribution of fecundity among breeders shifts from symmetrical to asymmetrical. In contrast, skew selection is a surplus model that assumes breeding occurs during a springtime glut. Skew selection assumes that fecundity among breeders is initially asymmetrical and that joining reduces the asymmetry of fecundity. This paper reports findings from a breeding experiment on the fire ant, Solenopsis invicta, which supported skew selection rather than reproductive skew. Joining was a win-win strategy for alpha and beta breeders; beta breeders gained within-group survival benefits; alpha breeders gained between-group survival benefits. In summary, skew selection extends Darwin’s theory of natural selection by revealing the self-interested core of cooperative breeding.


altruism social behavior reproductive fitness parental exploitation 

JEL classification

A13 B49 B59 C72 C91 D63 D64 J16 Z13 

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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • Deby L. Cassill
    • 1
  • Indira Kuriachan
    • 2
  • S. Bradleigh Vinson
    • 2
  1. 1.The University of South Florida St. PetersburgSt. PetersburgUSA
  2. 2.Department of EntomologyThe Texas A & M UniversityCollege StationUSA

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