Molecular systematics and biogeography of the Cockatoos (Psittaciformes: Cacatuidae)

Auk, The, Jan 1999 by Brown, David M, Toft, Catherine A

We sequenced part of the mitochondrial 12S ribosomal subunit gene for 15 species of cockatoos and then compared phylogenetic patterns derived from mtDNA with phylogenetic hypotheses from analysis of previously published allozyme data for 10 species of cockatoos (Adams et al. 1984), 7 of which were included in our study. We propose that the mtDNA phylogeny resolves the branching order of the cockatoo taxa and that current cockatoo taxonomy does not reflect accurately evolutionary relationships within the group. We suggest that Australia is the region of origin of cockatoos and that a combination of vicariance and dispersal resulted in two distinct radiations of the genus Cacatua in the islands north of the Australian continent.

METHODS

Materials and subjects.-Nomenclature follows Schodde (1997) for Australian species and Forshaw (1989) for non-Australian species. Tissue samples were acquired from captive birds, blood and shed feathers from living birds, and liver samples from birds that died of natural causes. Feather samples were obtained for Palm Cockatoo (Probosciger aterrimus), Blue-eyed Cockatoo (Cacatua ophthalmica), and Red-vented Cockatoo (C. haematuropygia). Blood was taken from Red-tailed Black-Cockatoo (Calyptorhynchus banks), Galah, Major Mitchell's Cockatoo, Sulphur-crested Cockatoo (Cacatua galerita), Lesser Sulphur-crested Cockatoo (C. sulphurea), Little Corella (C. sanguinea), Goffin's Cockatoo (C. goffini), Ducorps's Cockatoo (C. ducorps), Moluccan Cockatoo (C. moluccensis), Gang-gang Cockatoo, and Cockatiel. Liver samples were obtained for White Cockatoo (Cacatua alba).

We did not obtain material for Glossy Black-Cockatoo (Calyptorhynchus lathami), Yellow-tailed BlackCockatoo (C. funereus), White-tailed Black-Cockatoo (C. baudin), and Long-billed Corella (Cacatua tenuirostris). We assumed that the Calyptorhynchus group of black-cockatoos and the corella (Cacatua) group were adequately represented by Calyptorhynchus banks and Cacatua sanguinea, respectively, based on previous work (Adams et al. 1984: figure 2). We emphasize that the focus of our study is at the generic level, and we did not set out to resolve relationships of the lower taxa (i.e. species and subspecies).

Taxa used as outgroups were: Rock Dove (Columbia livia; feather), Common Canary (Serinus canariua; liver), and Japanese Quail (Coturnix japonica; sequence obtained from Desjardins and Morais [1991]). Selection of an appropriate outgroup for parrots has been problematic, likely because of the old age of this lineage (Dixon 1994). We selected Rock Dove (Columbiformes) and Common Canary (Passeriformes) as outgroups because both orders have been suggested as potential sister groups to the parrots (Dixon 1994, Sibley and Ahlquist 1990), and Japanese Quail because it was used by Dixon (1994). One possible problem with outgroup selection is that overly distant outgroups may ruin ingroup topologies by randomly selecting the longest ingroup branch as the root. We tested for this problem in the cockatoo tree by deleting all of the outgroup species to see whether the ingroup topology changed. Because the ingroup topology did not change when outgroup species were deleted, we assume that this particular problem with outgroup selection is not evident in the cockatoo tree.