Genetic evidence for species boundaries in frogs of the Litoria citropa species-group (Anura: Hylidae)

The Litoria citropa species-group comprises several small to medium-sized tree-frog species found from mid-eastern Queensland to eastern Victoria in a variety of habitats along streams associated with the Great Dividing Range. The smaller members of the Litoria citropa species-group, Litoria phyllochroa and L. pearsoniana, have a confused taxonomic history with the taxonomic status of several populations, some regarded as endangered, still in doubt. Multi-locus allozyme electrophoretic profiles and nucleotide sequences of a portion of the mitochondrial 16S ribosomal RNA gene were used to examine the evolutionary relationships of populations that are a geographically comprehensive and morphologically representative sample of the species-group. These data demonstrate the presence of a minimum of three species: L. nudidigitus, L. phyllochroa and a third species whose taxonomic name is yet to be resolved. This third taxon encompasses a wide range of allozyme and mitochondrial nucleotide diversity and can be divided into at least four evolutionarily significant units (ESUs) that replace each other in a linear sequence from north of the Hunter Valley in New South Wales to the Kroombit Tops in central Queensland. A possible zone of hybridisation between the southernmost pair of these ESUs was identified in northern New South Wales. The fourth ESU, a northern outlier of the range of the species-group, is confined to Kroombit Tops, central Queensland. While its phylogenetic relationship with the other three ESUs was not resolved precisely by the present analysis, it nevertheless comprises a distinct and very divergent mitochondrial lineage of considerable antiquity. Resolution of the status of a further name applied to the species-group, L. piperata, awaits a morphological analysis that includes the relevant type material.