Le rôle de la variation phénotypique dans l'evolution urbaine

Evaluating how eco-evolutionary processes drive individual diversity in natural systems has been a central focus in Evolutionary Ecology and numerous studies now examine individual phenotypic differences along environmental gradients. Genetic differences between individuals and phenotypic plasticity can both shape the total phenotypic variation observed within wild populations, and distinguishing the relative contributions of genetic and plastic effects is crucial for establishing the eco-evolutionary consequences of variation. Urban systems, specifically, are useful contexts to test how eco-evolutionary processes affect variation as phenotypic differentation is occuring on contemporary time scales across replicated urban contexts. Although it has been widely recognized that urbanization can affect the mean phenotypes of populations, whether genetic or plastic changes drive these urban phenotypic shifts and how urbanization affects overall phenotypic varaition is not well known. My thesis’ main objective is to determine how urbanization affects phenotypic variation in wild populations and to evaluate how genetic and environmental effects may contribute to differences in phenotypic variation along urban gradients.My thesis uses both meta- and mega-analyses with long-term datasets on replicated wild populations and experimental approaches to address my objectives. I first used meta- and mega-analyses with data on great and blue tits (Parus major, Cyanistes caeruleus) along 14 urban gradients across the European continent (Chapters 2 and 3) to evaluate how urbanization impacts morphological and life history variation. I establish that urbanization increases phenotypic variation (Chapters 2 and 3). More specifically, I find that urbanization increases individual differences at fine local scales within subpopulations and can also drive higher differentiation among urban subpopulations at larger spatial scales (Chapter 3).To examine how genetic and plastic change contribute to phenotypic divergences in urban populations, I used a common garden experiment with great tits along an urban gradient in Montpellier, France. I find that both genetic and plastic effects can contribute to wild urban phenotypes, and that their contributions are trait-specific. I show that genetic change likely contributes to smaller urban body size and faster breath rates, whereas plasticity to urban conditions most likely drives higher aggression and exploration behaviours in urban birds (Chapter 4). I also examine cognitive variation in wild great tits along the Montpellier urban gradient for the first time, and evaluate the genetic basis of this cognitive variation in the common garden experiment. I demonstrate that wild tits in more urbanized habitats have higher performance related to inhibitory control in a motor detour task compared to forest tits. However, these increased inhibitory control abilities are not maintained in the common garden context suggesting that the cognitive variation observed in the wild is likely driven by plasticity or experince in urban environments (Chapter 5).Overall, my thesis establishes that urbanization is associated with increases in phenotypic variation in wild populations at multiple spatial scales, and that both genetic and plastic changes contribute to urban phentoypic divergences. Thus, my results suggest that phentoypic variation can play an important role in urban evolution. My thesis illustrates that both multi and single population research studies can make useful contributions to Urban Evolutionary Ecology moving forward, and I discuss that integrating community ecology and climate change themes in urban research could be especially effective research avenues to promote further advances in urban research.

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