Impact of hybridisation in two Cossypha robin-chat species in southern Africa

Chorister Robin-Chat Cossypha dichroa , a South African forest endemic, and Red-capped Robin-Chat C. natalensis , a widely distributed species in African forest and woodland, are inferred to hybridise in areas of sympatry. DNA was extracted from blood samples of C. dichroa (n = 18), C. natalensis (n = 47), and two phenotypic hybrids. The mitochondrial cytochrome c oxidase I (COI) gene was amplified by PCR and sequenced. Phylogenetic analysis was performed on the sequence data to investigate taxonomic status and putative interspecific hybridisation. Phenotypic hybrids grouped with C. natalensis , suggesting maternal parentage from that species. Intra- and interspecific genetic and geographic distances were compared between C. dichroa and C. natalensis to assess genetic introgression. Seven of the thirteen microsatellite primer pairs developed for C. natalensis cross amplified in C. dichroa . These seven markers were then used for further analysis. STRUCTURE v2.3.4 was used to assign individuals to a particular genetic cluster and determine any admixture. NEWHYBRIDS v1.1 was used to assign hybrid status to samples beyond the F1 generation. Despite the hybridisation events recorded between C. dichroa and C. natalensis they still form two separate clusters as expected, and two genetic clusters (K=2) were identified using STRUCTURE. These two species are proficient vocal mimics and it is likely that reproductive isolation mechanisms are overcome through vocalisations. Genotypic hybrids are evident in the sampled population and hybridisation and backcrossing across a zone of sympatry is occurring. However, hybridisation is expected to have very little evolutionary influence on the integrity of recently diverged species which retain reproductive isolation across a wide region of sympatry through call distinctness.