Rapid phenotypic evolution during incipient speciation in a continental avian radiation

LEONARDO CAMPAGNA; PILAR BENITES; STEPHEN C. LOUGHEED; DARÍO A. LIJTMAER; ADRIÁN S. DI GIACOMO; MUIR D. EATON; PABLO L. TUBARO

Ottawa

Congreso; First Joint Congress on Evolutionary Biology; 2012

Canadian Society for Ecology and Evolution, European Society for Evolutionary Biology, Society for the Study of Evolution, Society of Systematics Biology

Classic examples of recent radiations such as Darwin´s finches, Hawaiian fruit flies and African Great Lakes cichlids have helped shape how we view animal speciation, providing key insight into the early stages of diversification. Here we identify a new case of a recent bird radiation within a continentally distributed species group; southern capuchino seedeaters comprise 9 Sporophila species originally described on the basis of differences in plumage color and pattern in adult males. We combine molecular data with spectrophotometric analysis of plumage and the study of sonograms derived from male vocalizations to understand species limits of the group. Contrasting with lack of mtDNA monophyly and low levels of differentiation in other putatively neutral markers (nuclear introns and DNA microsatellites), we find striking diversity in male coloration pattern and song that is maintained in sympatry, suggesting that the existing species in the group are not a taxonomic artifact. This is further substantiated by plumage differences found between southern capuchino females that are imperceptible to the human eye. Field experiments designed to evaluate male response to playback in two species (S. hypoxantha and S. palustris) suggest that at least these southern capuchinos distinguish between conspecific and heterospecific song, virtually ignoring the latter. These findings are consistent with the group having undergone a recent radiation beginning in the Pleistocene, leaving genetic signatures of incomplete lineage sorting, introgressive hybridization and demographic expansions. We suggest sexual selection could have had a predominant role in shaping this radiation and argue that the apparent uncoupling between neutral DNA homogeneity and phenotypic diversity is expected for a recent group, within the framework of coalescent theory.