Multilocus molecular DNA variation in Winifred’s Warbler Scepomycter winifredae suggests cryptic speciation and the existence of a threatened species in the Rubeho–Ukaguru Mountains of Tanzania

Winifred’s Warbler Scepomycter winifredae has a disjunct but very restricted distribution in the mountains of central Tanzania. It was once known only from the Uluguru Mountains. Subsequently, this rare warbler has been recorded from the Ukaguru Mountains, and more recently from the Rubeho Mountains, as well as from Mwanihana Forest on the eastern scarp of the Udzungwa Highlands (single record). These three localities are isolated from the Uluguru Mountains by more than 100 km of lowland savannah. Here we characterize the populations morphologically and estimate demographic parameters using a multilocus molecular approach. Birds from the Uluguru Mountains differed from those of the Rubeho–Ukaguru Mountains in mtDNA by 1.6% (uncorrected) sequence divergence, or at 16 sites: one at each of the first and second codon positions, and at 14 third codon position sites. Five autosomal introns were also sequenced for a total of 2922 bp of nuclear DNA. No single nucleotide polymorphisms were completely fixed between the Uluguru and Rubeho–Ukaguru populations. Results from our coalescent analyses suggest that there is currently unlikely to be any exchange of birds between the Uluguru and Rubeho–Ukaguru populations and that the shared nuclear alleles are a consequence of lineage sorting not yet having been completed due to the recent divergence (upper Pleistocene) between these two populations. In view of the lack of gene flow between the Uluguru and Rubeho–Ukaguru populations, and morphological diagnosability, we propose to recognize the latter populations as a separate species, which we name Rubeho Warbler Scepomycter rubehoensis.