Social selection is density dependent but makes little contribution to total selection in New Zealand giraffe weevils

David Fisher* (Corresponding Author), Rebecca J. LeGrice, Christina J. Painting

*Corresponding author for this work

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Social selection occurs when traits of interaction partners influence an indi- vidual’s fitness and can alter total selection strength. However, we have little idea of what factors influence social selection’s strength. Further, social selec- tion only contributes to overall selection when there is phenotypic assortment, but simultaneous estimates of social selection and phenotypic assortment are rare. Here, we estimated social selection on body size in a wild population of New Zealand giraffe weevils (Lasiorhynchus barbicornis). We measured phenotypic assortment by body size and tested whether social selection varied with sex ratio, density and interacted with the body size of the focal individual. Social selection was limited and unaffected by sex ratio or the size of the focal individual. However, at high densities social selection was negative for both sexes, consistent with size-based com- petitive interactions for access to mates. Phenotypic assortment was always close to zero, indicating negative social selection at high densities will not impede the evolution of larger body sizes. Despite its predicted importance, social selection may only influence evolutionary change in specific contexts, leaving direct selection to drive evolutionary change.
Original languageEnglish
Article number20210696
Number of pages8
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1952
Publication statusPublished - 9 Jun 2021


  • brentine
  • density dependent
  • fitness
  • phenotypic assortment
  • social selection
  • weevil


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