Phenotypic and genotypic variation across a stable white-eye (Zosterops sp.) hybrid zone in central South Africa

The interbreeding of two species after a period of separation (secondary contact) most often results in stable areas of hybridization or tension zones characterized by selection against hybrid individuals. Three plumage forms of Zosterops meet and interbreed in central South Africa. Here we examine how phenotypic measures (biometric and plumage) and genotypic markers (mitochondrial and nuclear DNA) change through a putative hybrid zone located in the area where the ranges of the Orange River white-eye Zosterops pallidus and a subspecies of the Cape white-eye Zosterops virens capensis meet. Four of the five sequenced loci (i.e. ATP6, MUSK, GADPH and TGF-β2) showed strong divergence and differentiation between allopatric parental populations, whereas the sex-linked CHD1Z locus exhibited high homogeneity. Microsatellite data also distinguished between pure Z. pallidus and Z. v. capensis populations. Together, the nuclear data (introns and microsatellites) identified at least 12 hybrid indi...