Congruence of phenotypic and genetic variation at the subspecific level in a Neotropical passerine

Abstract

The increasing availability of molecular phylogenies has highlighted the issue that genotypic and phenotypic patterns of variation are not always congruent, particularly below the species level. This has led to an ongoing discussion on the validity of the subspecies category and on the use of molecular data to help revise traditional classifications based on phenotypic data. We compared patterns of spatial diversification in genotype and phenotype in the Blue‐black Grosbeak Cyanocompsa cyanoides, a Neotropical songbird with four recognized subspecies. Variation in phenotype and genotype are partially congruent among the four subspecies. The more genetically divergent subspecies C. c. rothschildii is strongly differentiated from the other subspecies in morphological characters, plumage coloration and song. We suggest that this taxon be accorded full species status as Cyanocompsa rothschildii. Regarding the remaining diversity within C. cyanoides, both phenotypic and genetic markers suggest that it could be divided into two subgroups, but the boundaries of genetic lineages do not coincide with those of subspecies defined using phenotypic data. Lack of complete congruence between phenotypic and molecular markers may be expected, as they are subject to different evolutionary processes. The discordance could also be due to a methodological problem, as subspecies' geographical boundaries were defined on the basis of phenotypic descriptions that were not systematically evaluated. We consider the subspecies to be an informative taxonomic entity, but note that many current subspecific designations for diverse species need extensive reassessment.