Taxonomic status of the Liberian Greenbul Phyllastrephus leucolepis and the conservation importance of the Cavalla Forest, Liberia

The Liberian Greenbul Phyllastrephus leucolepis is known only from the Cavalla Forest, Liberia, where it was seen between 1981 and 1984 but has not been found since the collection of the type, and only, specimen. It is similar to the common and widespread Icterine Greenbul P. icterinus, from which it differs primarily in having white subterminal spots on the wing coverts and all flight feathers. Its validity as a distinct species has been questioned but left unresolved. This paper describes the first genetic study of the Liberian Greenbul, to attempt to determine whether it is a distinct species, a plumage variant of Icterine Greenbul, or a hybrid. Total genomic DNA was isolated independently by two separate laboratories from the type specimen, as well as from Icterine and White-throated Greenbuls P. albigularis sampled close to the type locality in Liberia. Mitochondrial and nuclear DNA was sequenced and compared to that of Icterine and other greenbul species from Liberia and elsewhere. Sequence analysis of three mitochondrial genes and one nuclear gene showed that the Liberian Greenbul is not a hybrid but falls within the range of intraspecific genetic variation observed in the Icterine Greenbul. Reasons for this are discussed, but the most likely explanation is that the Liberian Greenbul represents a plumage variant of the Icterine Greenbul. The alternative possibilities that the Liberian Greenbul represents a distinct species which only recently diverged or has ongoing gene flow with the Icterine Greenbul cannot be formally refuted. Conservation implications for the Cavalla Forest are discussed.