Aim Seasonal bird migration is one of the most fascinating global ecological phenomena. Yet, the biogeographic scenarios and climatic drivers that led single species or entire lineages to evolve seasonal migration between disjunct breeding and wintering ranges remain unclear. Based on distribution and phylogenetic data for all birds worldwide, we explored the biogeographic and climatic context of the evolutionary emergence of seasonal geographic migration in birds. Location Global. Taxon The Aves class (9,819 species). Methods We used the worldwide phylogeny of all birds, with a new backbone tree, to test the link between birds’ migration distance (short, variable, long) and strategy (resident, mixed, strict migrant) with four different metrics depicting species’ thermal niches in their breeding and wintering ranges. We also performed ancestral state reconstructions for the main migratory orders to reconstruct past events of appearance and loss of migration behaviour, and past biogeographic scenarios that led to the emergence of seasonal geographic migration. Results Migratory species generally experience warmer climates in their wintering range compared to their breeding one, although notable exceptions exist. This thermal niche change due to migration was found to be much larger for species travelling large distances. We also found that geographic migration emerged at different time periods through varied biogeographic paths (i.e. both from temperate and tropical ancestors) and that migration behaviour was likely ancestral to Passeriformes, with several subsequent episodes of loss of migration behaviour. Main conclusions We report an evolutionary correlation between long‐distance migration and the tendency of birds to seek warmer climates during their non‐breeding period, compared to short‐distance migrants. Migration behaviour was likely ancestral to Passeriformes, and migratory lineages in general seem to have often adapted to novel ecological opportunities by returning to a resident state. Our results provide the first large‐scale study of biogeographic and climatic origins of bird migration worldwide.

The genetic variance-covariance matrix (G-matrix) summarizes the genetic architecture of multiple traits. It has a central role in the understanding of phenotypic divergence and the quantification of the evolutionary potential of populations. Laboratory experiments have shown that G-matrices can vary rapidly under divergent selective pressures. However, due to the demanding nature of G-matrix estimation and comparison in wild populations, the extent of its spatial variability remains largely unknown. In this study, we investigate spatial variation in Gmatrices for morphological and life-history traits using long-term data sets from one continental and three island populations of Blue tit (Cyanistes caeruleus), which have experienced contrasting population history and selective environment. We found no evidence for differences in G-matrices among populations. Interestingly, the phenotypic variance-covariance matrices (P) were divergent across populations, suggesting that using P as a substitute for G may be inadequate. These analyses also provide the first evidence in wild populations for additive genetic variation in the incubation period (i.e. the period between last egg laid and hatching) in all four populations. Altogether, our results suggest that G-matrices may be stable across populations inhabiting contrasted environments therefore challenging the results of previous simulation studies and laboratory experiments.

a global database for metacommunity ecology, integrating species, traits, environment and space alienor Jeliazkov et al. #the use of functional information in the form of species traits plays an important role in explaining biodiversity patterns and responses to environmental changes. although relationships between species composition, their traits, and the environment have been extensively studied on a case-by-case basis, results are variable, and it remains unclear how generalizable these relationships are across ecosystems, taxa and spatial scales. to address this gap, we collated 80 datasets from trait-based studies into a global database for metaCommunity Ecology: Species, Traits, Environment and Space; "CEStES". Each dataset includes four matrices: species community abundances or presences/absences across multiple sites, species trait information, environmental variables and spatial coordinates of the sampling sites. the CEStES database is a live database: it will be maintained and expanded in the future as new datasets become available. By its harmonized structure, and the diversity of ecosystem types, taxonomic groups, and spatial scales it covers, the CEStES database provides an important opportunity for synthetic trait-based research in community ecology. Background & SummaryA major challenge in ecology is to understand the processes underlying community assembly and biodiversity patterns across space 1,2 . Over the three last decades, trait-based research, by taking up this challenge, has drawn increasing interest 3 , in particular with the aim of predicting biodiversity response to environment. In community ecology, it has been equated to the 'Holy Grail' that would allow ecologists to approach the potential processes underlying metacommunity patterns 4-7 . In macroecology, it is common to study biodiversity variation through its taxonomic and functional facets along gradients of environmental drivers 8-10 . In biodiversity-ecosystem functioning research, trait-based diversity measures complement taxonomic ones to predict ecosystem functions 11 offering early-warning signs of ecosystem perturbation 12 .The topic of Trait-Environment Relationships (TER) has been extensively studied across the globe and across the tree of life. However, each study deals with a specific system, taxonomic group, and geographic region and uses different methods to assess the relationship between species traits and the environment. As a consequence, we do not know how generalizable apparent relationships are, nor how they vary across ecosystems, realms, and taxonomic groups. In addition, while there is an emerging synthesis about the role of traits for terrestrial plant communities 13,14 , we know much less about other groups and ecosystem types.To address these gaps, we introduce the CESTES database -a global database for metaCommunity Ecology: Species, Traits, Environment and Space. This database assembles 80 datasets from studies that analysed empirical multivariate trait-environment relationships between 1996 (the first...