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The Riverine Barriers Hypothesis (RBH) posits that tropical rivers can be effective barriers to gene flow, based on observations that range boundaries often coincide with river barriers. Over the last 160 years, the RBH has received attention from various perspectives, with a particular focus on vertebrates in the Amazon Basin. To our knowledge, no molecular assessment of the RBH has been conducted on birds in the Afrotropics, despite its rich avifauna and many Afrotropical bird species being widely distributed across numerous watersheds and basins. Here, we provide the first genetic evidence that an Afrotropical river has served as a barrier for birds and for their lice, based on four understory bird species collected from sites north and south of the Congo River. Our results indicate near-contemporaneous, Pleistocene lineage diversification across the Congo River in these species. Our results further indicate differing levels of genetic variation in bird lice; the extent of this variation appears linked to the life-history of both the host and the louse. Extensive cryptic diversity likely is being harbored in Afrotropical forests, in both understory birds and their lice. Therefore, these forests may not be “museums” of old lineages. Rather, substantial evolutionary diversification may have occurred in Afrotropical forests throughout the Pleistocene, supporting the Pleistocene Forest Refuge Hypothesis. Strong genetic variation in birds and their lice within a small part of the Congo Basin forest indicates that we may have grossly underestimated diversity in the Afrotropics, making these forests home of substantial biodiversity in need of conservation.

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Résumé.-Nous décrivons ici Laniarius willardi, une nouvelle espèce de la famille des Malaconotidae vivant au Rift Albertine, en Afrique. Le caractère morphologique le plus remarquable de cette espèce est un iris gris à bleu-gris. Ceci et des données morphométriques externes indiquent que L. willardi est différent des autres Laniarius. De plus, L. willardi est génétiquement différent et son plus proche parent est L. poensis camerunensis, au Cameroun. L. atrococcineus et L. leucorhynchus forment le clade saeur de L. willardi-L. p. camerunensis. L. willardi et L. p. holomelas, dont la répartition géographique est similaire, diffèrent de , % en ce qui concerne la divergence de la séquence corrigée. Les données altitudinales récoltées sur des spécimens de musée suggèrent qu'il existe une possibilité de ségrégation altitudinale des espèces à ~  m, L. willardi étant présent à des altitudes plus faibles. Notre vaste échantillonnage de ce taxon indique que () les races L. poensis ne forment pas un clade monophylétique, () L. p. camerunensis peut représenter des lignées multiples qui ne sont pas saeurs et () au moins une race de L. fuelleborni usambaricus est génétiquement distincte des autres races de cette espèce.-678 - In , T.P.G., C.K., and B.D.M. conducted collections-based field work in the southern region of Uganda, in the Albertine Rift system. Their survey was conducted on privately held property primarily used as a banana plantation, which included the only forest contiguous with the Bwindi Impenetrable National Park in the area. During this survey, they collected  black Laniarius specimens that they were forced to attribute to L. poensis holomelas on the basis of size and plumage characteristics. However, these specimens, and an additional Field Museum of Natural History (FMNH) specimen collected in Burundi in , were noted as having a unique iris color (gray to blue-gray) unlike that shown for any black Laniarius species in field guides (reddish-black to black). We could find no published reports describing blue-gray irides in adults of black Laniarius species, which reinforced concerns about the identification of these specimens (Marks et al. ).Further questions related to species limits and taxonomy of black Laniarius species are raised by the broader distributions of L. poensis and L. fuelleborni. The former has a significant geographic disjunction between subspecies in the Albertine Rift and Mt. Cameroon (Fig. ), and the latter has populations isolated on different mountains of the Eastern Arc, as well as a population in southwestern Tanzania and northern Malawi (Fry et al. ). Taxonomically, these two species have been linked; races of L. poensis were historically recognized as subspecies of L. fuelleborni (Mayr and Greenway ). Also, L. poensis and L. fuelleborni along with L. leucorhynchus are considered a superspecies (Fry et al. ). However, no phylogenetic study has addressed the relationships among these populations.We had two goals in the present study. First, we con...

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