Résumé
Urban phenotypic divergences are documented across diverse taxa, but the
underlying genetic and environmental drivers behind these phenotypic
changes are unknown in most wild urban systems. We conduct a common garden
experiment using great tit (Parus major) eggs collected along an
urbanization gradient to: 1) determine whether documented morphological,
physiological, and behavioural shifts in wild urban great tits are
maintained in birds from urban and forest origins reared in a common
garden (N = 73) and 2) evaluate how different sources of genetic, early
maternal investment, and later environmental variation contributed to
trait variation in the experiment. In line with the phenotypic divergence
in the wild, common garden birds from urban origins had faster breath
rates (i.e., higher stress response) and were smaller than birds from
forest origins, while wild differences in aggression and exploration were
not maintained in the experiment. Differences between individuals (genetic
and environmentally induced) explained the most trait variation, while
variation among foster nests and captive social groups was limited. Our
results provide trait-specific evidence of evolution in an urban species
where genetic change likely underlies urban differences in morphology and
stress physiology, but that urban behavioural divergences are more
strongly driven by plasticity.