Diversification of Petroica robins across the Australo-Pacific region: first insights into the phylogenetic affinities of New Guinea’s highland robin species

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© 2018, © 2018 BirdLife Australia. Complex spatial and temporal phylogenetic patterns have emerged among Pacific Island radiations and their Australian and New Guinean congeners. We explore the diversification of Australo-Pacific Petroica robins using the first phylogeny with complete species-level sampling of the genus. In doing so we provide the first assessment of the phylogenetic affinities of two poorly known species with highly restricted ranges in the highlands of New Guinea–Subalpine Robin (Petroica bivittata) and Snow Mountain Robin (P. archboldi). Our analyses suggest that Petroica underwent an initial diversification during the Plio-Pleistocene that established four major lineages restricted to New Zealand (four species), Australia (four species), New Guinea (two species) and Pacific Islands + Australia (three or four species). All lineages appear to have undergone species diversification in situ with the exception of the Pacific Islands + Australia lineage where long-distance over-water dispersal must be invoked to explain the placement of the Red-capped Robin (P. goodenovii) within the iconic Pacific robin species complex (P. multicolor + pusilla). Two scenarios fit this biogeographic pattern: (1) a single ‘upstream’ colonisation of mainland Australia from a Pacific Island ancestor resulting in P. goodenovii, or (2) two or three ‘downstream’ colonisations from a mainland Australian or New Guinean ancestor resulting in the distinct Pacific robin lineages that occur in the south-west Pacific. Overall, biogeographic patterns in Petroica suggest that long-distance dispersal and island colonisations have been rare events in this group, which contrasts with other Australo-Pacific radiations that show evidence for repeated long-distance dispersals and multiple instances of secondary sympatry on islands across the Pacific.

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