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Evolution. 2016 Jun;70(6):1307-21. doi: 10.1111/evo.12950. Epub 2016 Jun 1.

Social selection parapatry in Afrotropical sunbirds.

Author information

Museum of Vertebrate Zoology and Department of Integrative Biology, University of California, Berkeley, California, 94720.
Current Address: Department of Biology, University of Florida, P. O. Box 118525, 220 Bartram Hall, Gainesville, Florida, 32611.
Museum of Vertebrate Zoology and Department of Integrative Biology, University of California, Berkeley, California, 94720.
Current Address: Australian National University, Canberra.
Department of Zoology and Wildlife Conservation, University of Dar-es-salaam, Dar-es-salaam, Tanzania.
P. O. Box 934, Iringa, Tanzania.
Tanzania Bird Atlas, Iringa, Tanzania.
Field Museum of Natural History, Chicago, Illinois, 60605.
Center for Macroecology, Evolution and Climate, University of Copenhagen, Denmark.


The extent of range overlap of incipient and recent species depends on the type and magnitude of phenotypic divergence that separates them, and the consequences of phenotypic divergence on their interactions. Signal divergence by social selection likely initiates many speciation events, but may yield niche-conserved lineages predisposed to limit each others' ranges via ecological competition. Here, we examine this neglected aspect of social selection speciation theory in relation to the discovery of a nonecotonal species border between sunbirds. We find that Nectarinia moreaui and Nectarinia fuelleborni meet in a ∼6 km wide contact zone, as estimated by molecular cline analysis. These species exploit similar bioclimatic niches, but sing highly divergent learned songs, consistent with divergence by social selection. Cline analyses suggest that within-species stabilizing social selection on song-learning predispositions maintains species differences in song despite both hybridization and cultural transmission. We conclude that ecological competition between moreaui and fuelleborni contributes to the stabilization of the species border, but that ecological competition acts in conjunction with reproductive interference. The evolutionary maintenance of learned song differences in a hybrid zone recommend this study system for future studies on the mechanisms of learned song divergence and its role in speciation.


Bird song; HZAR; cline; hybrid zone; sexual selection; species borders

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