Résumé
Increasing urbanisation offers a unique opportunity to study adaptive
responses to rapid environmental change. Numerous studies have
demonstrated phenotypic divergence between urban and rural organisms.
However, comparing the direction and magnitude of natural selection
between these environments has rarely been attempted. Using seven years of
nest-box breeding monitoring of great tits (Parus major) in the city of
Montpellier and in a nearby oak forest, we find phenotypic divergence in
four morphological and two life-history traits between urban and forest
birds. We then measure reproductive selection on these traits, and compare
selection between the habitats. Urban birds had significantly smaller
morphological features than their rural counterparts, with shorter tarsus,
lower body mass and smaller wing and tail lengths relative to their
overall body size. While urban female tarsus length was under stabilising
selection, and forest males show positive selection for tarsus length and
negative selection for body mass, selection gradients were significantly
divergent between habitats only for body mass. Urban great tits also had
earlier laying dates and smaller clutches. Surprisingly, we found
selection for earlier laying date in the forest but not in the city.
Conversely, we detected no linear selection on clutch size in the forest,
but positive selection on clutch size in the urban habitat. Overall, these
results do not support the hypothesis that contemporary reproductive
selection explains differences in morphology and life history between
urban and forest breeding great tits. We discuss how further experimental
approaches will help confirm whether the observed divergence is
maladaptive while identifying the environmental drivers behind it.