Data from: The role of selection and historical factors in driving population differentiation along an elevational gradient in an island bird

Adaptation to local environmental conditions and the range dynamics of populations can influence evolutionary divergence along environmental gradients. Thus, it is important to investigate patterns of both phenotypic and genetic variation among populations to reveal the respective roles of these two types of factors in driving population differentiation. Here, we test for evidence of phenotypic and genetic structure across populations of a passerine bird (Zosterops borbonicus) distributed along a steep elevational gradient on the island of Réunion. Using eleven microsatellite loci screened in 401 individuals from 18 localities distributed along the gradient, we found that genetic differentiation occurred at two spatial levels: (i) between two main population groups corresponding to highland and lowland areas, respectively, and (ii) within each of these two groups. In contrast, several morphological traits varied gradually along the gradient. Comparison of neutral genetic differentiation (FST) and phenotypic differentiation (PST) showed that PST largely exceeds FST at several morphological traits, which is consistent with a role for local adaptation in driving morphological divergence along the gradient. Overall, our results revealed an area of secondary contact mid-way up the gradient between two major, cryptic, population groups likely diverged in allopatry. Remarkably, local adaptation has shaped phenotypic differentiation irrespective of population history, resulting in different patterns of variation along the elevational gradient. Our findings underscore the importance of understanding both historical and selective factors when trying to explain variation along environmental gradients.ZoboGrad-GENEPOPIndividual genotypes of the 401 individuals at 12 microsatellite loci. This file is provided in the universal GENEPOP format. The first section corresponds to a list of the name of the loci. Then, each row represent a single individual: first column is the individual identifier and the following columns correspond to the length (concatenation of 2 x 3 digits) of the different alleles at the 12 loci (one column each). Sampling localities are separated by a empty lines.ZoboGrad-MorphoFile summarizing the morphological data for each individual. Each line corresponds to a single individual with informations about sampling localities, ringer and all the morphological variables measured: weight (g), wing length (mm), tail length (mm), tarsus length (mm), bill length (mm), bill depth (mm) and bill width (mm)