Evolutionary Ecology

, Volume 24, Issue 6, pp 1277–1290 | Cite as

Do seed-dispersing birds exert selection on optimal plant trait combinations? Correlated phenotypic selection on the fruit and seed size of hawthorn (Crataegus monogyna)

  • Mar Sobral
  • Asier R. Larrinaga
  • José Guitián
Original Paper


Seed-dispersing birds can be expected to optimize their energy intake through fruit selection and hence exert a positive selection on fruit pulp content, that is to say, favoring big fruits with small seeds. On the other hand they may select both, average fruit size and its variation. We addressed this issue by analyzing the phenotypic selection exerted by the dispersers of Crataegus monogyna on the fruit and seed size of this species. Fruit and seed size were analyzed at two ontogenic plant stages: the initial size of seeds (and their fruits) as future individuals and the mean size of fruits and seeds produced by adult plants. Fruit diameter and its within-individual variation are the actual targets of selection for maternal fruit traits, negatively affecting relative fitness, although total selection acts only on mean fruit size. For individual seeds, size selection is positive and directed at fruit diameter and seed length, while the remaining traits are subject to indirect selection. Birds exerted a correlational selection favoring big fruits with small seeds. Nevertheless the evolutionary consequences of this selection are expected to be limited by several factors. For example, the positive correlation between fruit and seed sizes, the existence of counteracting selective pressures exerted by other mutualistic or antagonist interactions and temporal or spatial changes in the environmental conditions that may alter the selective forces and even the optimum phenotype in each situation.


Initial and maternal seed size Selection differential Selection gradient Within-individual variation 



We would like to thank Patricia M. Leyenda for her untiring support during the field work and César Sanchez for statistical advice. Pablo Guitián revised the manuscript and made useful suggestions. This work was supported by the Spanish Ministry of Science and Education (project CGL2005-03826) and the European Commission (FEDER program).


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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  • Mar Sobral
    • 1
  • Asier R. Larrinaga
    • 2
  • José Guitián
    • 3
  1. 1.Facultade de BioloxíaUniversity of Santiago de CompostelaSantiago de CompostelaSpain
  2. 2.Institut Mediterrani d’Estudis Avançats (I.M.E.D.E.A)MallorcaSpain
  3. 3.Facultade de BioloxíaUniversity of Santiago de CompostelaSantiago de CompostelaSpain

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