Exploring subindividual variability: role of ontogeny, abiotic environment, and seed-dispersing birds.

Within-individual trait variation -otherwise known as subindividual variation- is an important component of phenotypic variation, with a genetic and epigenetic basis. We explore its adaptive value and the effects of ontogeny and the environment on subindividual variability. We conducted a field study to analyze the effects of tree age, soil pH, soil water content, and soil nutrients on subindividual variability in fruit size of Hawthorn (Crataegus monogyna) in three sites in Northwestern Spain. Additionally, we examined how bird-mediated selection influences average and subindividual variation in fruit size. Results show that average and subindividual variation of fruit size were related to fitness affecting seed dispersal. Older trees produced larger fruits, but tree age did not affect subindividual variation in fruit size. Abiotic environmental factors differently affected subindividual variation and average fruit size. Seed-dispersing birds exerted correlated selection on fruit size average and variation, favoring trees with larger and less variable fruit size at one site. Our work suggests that the fruit size variation within individual trees, the subindividual variation, is modified by abiotic environmental factors and additionally it is an adaptive trait that responds to natural selection. This article is protected by copyright. All rights reserved.