A case for realigning species limits in the southern Australian whipbirds long recognised as the Western Whipbird (Psophodes nigrogularis)

The Western Whipbird (Psophodes nigrogularis) has a highly disjunct west–east distribution across southern Australia. Earlier morphological analyses recognised four subspecies in one species: P. n. nigrogularis and P. n. oberon in south-west Western Australia, and P. n. leucogaster of the Eyre and Yorke Peninsulas and the Murray Mallee, and P. n. lashmari, restricted to Kangaroo Island, both in eastern Australia. Later morphological analyses elevated P. n. nigrogularis to monotypic species rank, and placed the remaining western and two eastern taxa as three subspecies of a second species P. leucogaster. Initial mtDNA analysis questioned both arrangements but could not include all taxa. We used mtDNA sequence data from all available specimens of the entire group (DNA extracted from cryo-preserved tissues, toe-pads and feathers; holotypes excepted) to derive a more stable view of species limits. The samples fell into two strongly divergent but geographically structured groups, completely reflecting the eastern and western components of the distribution. Thus we see merit in treating the two geographical groupings as two species, P. nigrogularis in the west and P. leucogaster in the east, each having two subspecies. Nuclear data could test whether the two western subspecies in particular are genetically isolated or currently exchanging genes.

西澳鞭鸩（Western Whipbird，学名Psophodes nigrogularis）在澳大利亚南部呈现高度间断的东西向分布格局。早期形态学分析将该物种划分为4个亚种：分布于西澳大利亚州西南部的P. n. nigrogularis与P. n. oberon，以及分布于澳大利亚东部艾尔半岛、约克半岛和马里穆雷地区的P. n. leucogaster，还有仅栖息于袋鼠岛的P. n. lashmari。后续的形态学研究将P. n. nigrogularis提升为单型种，并将其余西部类群与两个东部类群归为第二个物种P. leucogaster的3个亚种。早期线粒体DNA（mtDNA）分析对上述两种分类处理均提出质疑，但未能纳入全部类群开展验证。本研究使用该类群所有可获取标本的线粒体DNA序列数据（DNA提取自低温保存组织、趾垫及羽毛，正模标本除外），以期对物种界定形成更为稳定的认知。研究样本被划分为两个分化显著且具有地理结构的类群，完全对应分布区内的东部与西部组分。因此，我们认为将这两个地理类群划分为两个物种更为合理：西部为P. nigrogularis，东部为P. leucogaster，每个物种各含2个亚种。后续可通过核基因组数据验证，尤其是西部的两个亚种是否存在遗传隔离，抑或正发生基因交流。