title: Mediterranean blue tits as a case study of local adaptation.
abstract: While the study of the origins of biological diversity across species has provided numerous examples of adaptive divergence, the realization that it can occur at microgeographic scales despite gene flow is recent, and scarcely illustrated. We review here evidence suggesting that the striking phenotypic differentiation in ecologically relevant traits exhibited by blue tits Cyanistes caeruleus in their southern range-edge putatively reflects adaptation to the heterogeneity of the Mediterranean habitats. We first summarize the phenotypic divergence for a series of life history, morphological, behavioural, acoustic and colour ornament traits in blue tit populations of evergreen and deciduous forests. For each divergent trait, we review the evidence obtained from common garden experiments regarding a possible genetic origin of the observed phenotypic differentiation as well as evidence for heterogeneous selection. Second, we argue that most phenotypically differentiated traits display heritable variation, a fundamental requirement for evolution to occur. Third, we discuss nonrandom dispersal, selective barriers and assortative mating as processes that could reinforce local adaptation. Finally, we show how population genomics supports isolation - by - environment across landscapes. Overall, the combination of approaches converges to the conclusion that the strong phenotypic differentiation observed in Mediterranean blue tits is a fascinating case of local adaptation.
authors.affiliation: Centre d'Ecologie Fonctionnelle et Evolutive Campus CNRS Montpellier France.
authors.forename: Anne
authors.initials: A
authors.lastname: Charmantier
authors.affiliation: Centre d'Ecologie Fonctionnelle et Evolutive Campus CNRS Montpellier France.
authors.forename: Claire
authors.initials: C
authors.lastname: Doutrelant
authors.affiliation: Centre d'Ecologie Fonctionnelle et Evolutive Campus CNRS Montpellier France; Département des sciences biologiques Université du Québec à Montréal Succursalle centre-ville QC Canada.
authors.forename: Gabrielle
authors.initials: G
authors.lastname: Dubuc-Messier
authors.affiliation: Centre d'Ecologie Fonctionnelle et Evolutive Campus CNRS Montpellier France.
authors.forename: Amélie
authors.initials: A
authors.lastname: Fargevieille
authors.affiliation: Centre d'Ecologie Fonctionnelle et Evolutive Campus CNRS Montpellier France.
authors.forename: Marta
authors.initials: M
authors.lastname: Szulkin
keywords: Cyanistes caeruleus; adaptive divergence; environment heterogeneity; genomic differentiation; genotype–environment association; heritability; isolation‐by‐environment; phenotypic differentiation; phenotypic plasticity