Thursday, November 15, 2012

[Ornithology • 2011] The Evolutionary History of Cockatoos (Psittaciformes: Cacatuidae)

Fig. 1. Illustrations of eight adult male cockatoo species showing variation in plumage and morphology; (A) Palm Cockatoo (Probosciger aterrimus); (B) Gang-gang Cockatoo (Callocephalon fimbriatum); (C) Galah (Eolophus roseicapillus); (D) Sulphur-crested Cockatoo (Cacatua galerita); (E) Western Corella (Cacatua pastinator); (F) Baudin’s Black-cockatoo (Calyptorhynchus baudinii); (G) Glossy Black-cockatoo (Calyptorhynchus lathami); and (H) Cockatiel (Nymphicus hollandicus). Artist: J.N. Davies

Cockatoos are the distinctive family Cacatuidae, a major lineage of the order of parrots (Psittaciformes) and distributed throughout the Australasian region of the world. However, the evolutionary history of cockatoos is not well understood. We investigated the phylogeny of cockatoos based on three mitochondrial and three nuclear DNA genes obtained from 16 of 21 species of Cacatuidae. In addition, five novel mitochondrial genomes were used to estimate time of divergence and our estimates indicate Cacatuidae diverged from Psittacidae approximately 40.7 million years ago (95% CI 51.6–30.3 Ma) during the Eocene. Our data shows Cacatuidae began to diversify approximately 27.9 Ma (95% CI 38.1–18.3 Ma) during the Oligocene. The early to middle Miocene (20–10 Ma) was a significant period in the evolution of modern Australian environments and vegetation, in which a transformation from mainly mesic to xeric habitats (e.g., fire-adapted sclerophyll vegetation and grasslands) occurred. We hypothesize that this environmental transformation was a driving force behind the diversification of cockatoos. A detailed multi-locus molecular phylogeny enabled us to resolve the phylogenetic placements of the Palm Cockatoo (Probosciger aterrimus), Galah (Eolophus roseicapillus), Gang-gang Cockatoo (Callocephalon fimbriatum) and Cockatiel (Nymphicus hollandicus), which have historically been difficult to place within Cacatuidae. When the molecular evidence is analysed in concert with morphology, it is clear that many of the cockatoo species’ diagnostic phenotypic traits such as plumage colour, body size, wing shape and bill morphology have evolved in parallel or convergently across lineages.

► The phylogeny of cockatoos is resolved using mitochondrial and nuclear DNA data. ► The common ancestor of cockatoos lived ca. 27.9 million years ago. ► Plumage colour, body size, wing shape and bill morphology are highly plastic. ► The phylogeny will assist in conservation, taxonomy and policing illegal bird trade.

Parrot; Phylogeny; Molecular dating; Mitochondrial genome; Avian evolution; Phenotypic plasticity

2011. The evolutionary history of cockatoos (Aves: Psittaciformes: Cacatuidae)