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.