Does nuclear DNA support the recognition of three species within the Splendid Fairywren Malurus splendens?

The Splendid Fairywren Malurus splendens has four distinct phenotypic forms currently recognised as subspecies, although three species have been recognised within the group in the past. Here, we use multilocus nuclear DNA to test the recent hypothesis that the Splendid Fairywren represents three allopatric taxa with little to no modern-day contact, despite phenotypic evidence of periods of past contact and gene flow. Our nuclear dataset is concordant with earlier mtDNA-based data in supporting three distinct genetic groups within M. splendens. These genetic groups align with the three phenotypically distinct forms recently hypothesised to be allopatric and previously described at species-level – western M. splendens, central M. callainus and eastern M. melanotus. Nuclear gene flow does not appear to be rampant between the three forms; however, several individuals show signals of admixed nuclear ancestry, which we cannot distinguish as having resulted from incomplete lineage sorting, poor phylogenetic signal, or gene flow. Given changing modern taxonomic interpretations of the significance of gene flow in speciation, we argue that recognising three distinct species within the M. splendens complex might better represent their evolutionary distinctiveness, rather than continuing to treat these genetically and morphologically distinct forms as subspecies of a widespread polytypic species. Our study highlights the interesting complexity of determining species status when taxa are in the 'grey zone' near the subspecies/species continuum, and the value gained from adding perspectives from nuclear DNA. [ABSTRACT FROM AUTHOR]