Evolutionary Divergences in Luscinia Svecica Subspecies Complex – New Evidence Supporting the Uniqueness of the Iberian Bluethroat Breeding Populations

The assessment of evolutionary divergences within subspecies complexes provide an effective short-cut for estimating intraspecific genetic diversity, which is relevant for conservation actions. We explore new evidence supplementing the existing knowledge about the singularity of Iberian bluethroats within the Luscinia svecica subspecies mosaic. We compared biometric traits of Iberian males (L. s. azuricollis) to the closest subspecies (L. s. cyanecula, L. s. namnetum and L. s. magna) using general linear models and analysed the correlations between biometric and genetic differentiation (based on nuclear micro-satellites) among the target subspecies with a Mantel test. Biometric differences were calculated using 63 museum skins and 63 live specimens. Genetic distances were estimated in a sample of 136 individuals. An additional characterisation of the plumage of Iberian males was shaped from 22 live specimens. We highlight the distinctiveness of Iberian birds within the subspecies mosaic since L. s. azuricollis had longer wings than L. s. cyanecula and L. s. namnetum, but shorter wings than L. s. magna. Indeed, L. s. azuricollis had longer tarsus and bill than L. s. namnetum, but shorter bill than L. s. magna. Biometric divergence was not significantly associated with genetic distance. Iberian males showed an all-blue plastron in 77% of specimens, a mostly non-marked black band and no white band, which distinguished them from males of L. s. cyanecula and L. s. namnetum. We conclude the importance of considering phenotypic and genotypic differences at subspecies level, which is essential for designing realistic conservation strategies addressed to preserve species genetic diversity patterns.