Morphological bluethroat dataset

In temperate mountain ranges, sharp spatial variations in habitat heterogeneity and climate provide a perfect study setup to assess genetic and phenotypic differentiation in bird populations. In this paper, we analyzed morphological divergence patterns across geographic and environmental gradients, in correlation with genetic differentiation and geographic isolation, in the breeding grounds of a long-distance migrant passerine. Location NorthWestern Iberian mountains. Major taxa studied Iberian bluethroat, Luscina svecica azuricollis. Methods We collected a sample of 625 Iberian bluethroats across their whole breeding distribution area to measure body weight and tarsus length, as well as wing length and pointedness. Morphological differentiation across geographic (latitude and altitude) and environmental (climate and vegetation) gradients was assessed using GLMMs. Additionally, the role of genetic distance and geographic isolation as drivers of morphological differentiation was evaluated with Mantel tests. Results Bird morphology varied significantly with latitude and altitude, but not with climate or vegetation. In the case of latitude, morphological differences in body size were contrary to what was expected according to Bergmann's rule. All biometric and morphometric variables diverged significantly among localities. A similar trend was found for genetic clusters, except for the case of wing shape. Body weight and wing length were both correlated to geographical distance, while only the former varied with genetic differentiation. The greatest genetic and phenotypic differentiation was detected in the southernmost mountain range that holds the most geographically isolated genetic group. Main conclusion As expected, Iberian breeding bluethroats show strong latitudinal phenotypic differentiation that correlates with geographic isolation and genetic distance. Nevertheless, some deviances from this pattern occur for biometric variables with greater selective pressure, which points to local adaptations related to migratory strategies. On the opposite of what was hypothesized, body size was inversely correlated to latitude