Fine-scale life-history variation in sociable weavers in relation to colony size

Authors

  • Claire N. Spottiswoode

    Corresponding author
    1. Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK
    2. DST/NRF Centre of Excellence at the Percy FitzPatrick Institute, University of Cape Town, Rondebosch 7701, South Africa
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*Correspondence author. E-mail: cns26@cam.ac.uk

Summary

  • 1This study investigates the mechanistic and ecological basis of phenotypic sorting in the sociable weaver Philetairus socius (Latham). In this colonially and communally breeding African bird, morphology, condition, age-specific survival rates and reproductive investment vary with colony size.
  • 2This variation might arise from non-adaptive constraints imposed by density dependence, or from adaptive life-history responses to colony size-dependent selection pressures. To attempt to distinguish these, the environments in which adults made reproductive decisions and in which offspring developed were manipulated.
  • 3When food supplementation improved the pre-breeding environment of adults, they bred earlier but did not change investment in eggs or incubation.
  • 4Nestling and subsequent adult phenotypes were unaffected by supplementary feeding, although post-fledging survival improved. Nestling origin and not rearing environment predicted phenotype in a cross-fostering experiment between colonies.
  • 5Phenotypic differences among colonies hence seemed not to be plastic responses to resource availability. Life-history differentiation, mediated either genetically or maternally, might have taken place over relatively narrow temporal and spatial scales.
  • 6Adaptive variation in reproductive investment could thus mitigate costs of large colony size, by reducing costs of reproduction and hence improving adult survival. If so, then fine-scale life-history adjustment could help to maintain stable variation in colony size.

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