How far east can a Western Whistler go? Genomic data reveal large eastward range extension, taxonomic and nomenclatural change, and reassessment of conservation needs

ABSTRACT

The Western Whistler Pachycephala occidentalis Ramsay, 1878, endemic to south-western Western Australia, is almost phenotypically identical with P. pectoralis fuliginosa, the westernmost of six subspecies of Golden Whistler P. pectoralis on Australia and its islands. New mitochondrial DNA (mtDNA) sequence data affirm multiple prior studies in aligning P. pectoralis fuliginosa with other subspecies of P. pectoralis, not P. occidentalis. Conversely, principal coordinates and phylogenetic analyses of new data from >17,000 single nucleotide polymorphisms show P. occidentalis and P. pectoralis fuliginosa barely differentiated from each other, neither being close to any P. pectoralis subspecies. In earlier work, weak, ambiguous signal in nuclear DNA sequences possibly suggested close relationship between P. occidentalis and P. pectoralis fuliginosa but was ‘swamped’ by the phylogenetic signal of the mtDNA. Accordingly, we recognise one species, P. fuliginosa Vigors and Horsfield, 1827, having two subspecies P. fuliginosa occidentalis and P. fuliginosa fuliginosa. Western Whistler remains an appropriate English name for the species P. fuliginosa. MtDNA of Golden Whistler P. pectoralis is hypothesised to have introgressed westwards into the range of P. fuliginosa fuliginosa but not further west into P. fuliginosa occidentalis and we address this. Our conclusions open questions for the conservation of the Western Whistler, now known to have a greater breeding range spanning drier parts of South Australia and Victoria and, potentially, western New South Wales where its occurrence is still unproven. For example, what are the extents of seasonal range overlap, intergradation and niche differentiation of Golden and Western Whistlers in south-eastern Australia and of the two subspecies of Western Whistler?

KEYWORDS:

• Whistlers
• taxonomy
• Pachycephala
• biogeography
• speciation

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Acknowledgements

We are indebted to Karen Rowe, Tim Stranks and Jo Sumner (Museum Victoria, Melbourne), Leah Tsang (Australian Museum, Sydney), and Sharon Birks and Kevin Epperly (University of Washington, Burke Museum, Seattle) for data and photographs of specimens at their institutions. Richard Schodde helped with early discussions. Julian Teh prepared the illustrations. Inbar Maayan commented on a draft and Michael Lenz helped with literature. Specimens were collected in 2017 under Permit 08-000827-1 from the Department of Parks and Wildlife, Western Australia, and CSIRO Animal Ethics Permits 2015-16. Lynn Pedler and Mark Robbins helped with field work. Three reviewers and the editors made very helpful comments.

Disclosure statement

No potential conflict of interest was reported by the authors.

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