Abstract

The logrunners (Passeriformes: Orthonychidae: Orthonyx) of the montane rainforests of New Guinea are usually treated as conspecific with the Logrunner, Orthonyx temminckii, of central eastern Australia’s upland subtropical rainforests. We used partial mitochondrial DNA (mtDNA) sequences (cytochrome b and ATPase 8 and 6 genes), largely derived from museum specimens and supplemented with morphometric and plumage data, to re-examine relationships within and among New Guinean and Australian populations of logrunners. The mtDNA sequences from the New Guinean populations are monophyletic and deeply divergent from Australian ones. We cannot with certainty determine whether the sister taxon of the New Guinean populations is the Chowchilla, O. spaldingii, of north-east Queensland’s Wet Tropics or O. temminckii. Morphologically, the New Guinean birds are more divergent from Australian O. temminckii than has been appreciated, being significantly smaller and with far less white on their underparts. Their similarities to each other are almost certainly due to retention of ancestral plumage character states. Under any species concept their differences permit the New Guinean birds to be considered as a separate species, O. novaeguineae Meyer, 1874. Within O. novaeguineae, there is a deep phylogeographic break in the distribution of mtDNA diversity between its Vogelkop population in north-western New Guinea and its Snow Mountains and south-eastern highland populations (>5% net nucleotide diversity) in the Central Cordillera. The magnitude of this mtDNA break suggests that, as in endemic birds of the rainforests of north-eastern Queensland, vicariance has operated to fragment these birds’ populations at least since the beginning of the Pleistocene if not considerably earlier in the Plio-Miocene. The molecular divergence between Vogelkop and Central Cordillera populations is mirrored in morphology. Weak trends towards birds becoming darker and larger as one moves from west to east across New Guinea may be related to altitude. Taking a cue primarily from the patterns and magnitude of mtDNA divergence, we provisionally recommend taxonomic subdivision of O. novaeguineae.