Data from: Incorporating color into integrative taxonomy: analysis of the varied tit (Sittiparus varius) complex in East Asia

Species designations are critically important scientific hypotheses that serve as the foundational units in a wide range of biological subdisciplines. A growing realization that some classes of data fail to delimit species under certain conditions has led to increasingly more integrative taxonomies, whereby species discovery and hypothesis-testing are based on multiple different kinds of data (e.g. morphological, molecular, behavioral, ecological, etc.). However, although most taxonomic descriptions have been based on morphology, some key morphological features, such as color, are rarely quantified and incorporated into integrative taxonomic studies. In this paper, we applied a new method of ultraviolet digital photography to measure plumage variation in a color variable avian species complex, the varied tit (Sittiparus varius). Plumage measurements corroborated species limits defined by morphometric, mitochondrial DNA, and nuclear DNA disjunctions and provided the only evidence for recognizing two recently evolved species. Importantly, color quantification also provided a justification for lumping putative taxa with no evidence of evolutionary independence. Our revised taxonomy thus refines conservation units for listing and management and clarifies evolutionary units for biogeographic inquiry. Phylogenetic species tree analyses, which applied newly delimited species as operational taxonomic units, revealed a south to north colonization history within the varied tit complex that was inconsistent with the prevailing paradigm of historical landbridge connections in East Asia; this establishes a foundation for integrating the biogeographic patterns of volant taxa into a comparative framework of the East Asian landbridge region. Overall, our study demonstrates that digital photography provides a powerful tool for incorporating color character variation into integrative taxonomies, which should lead to more informed, more rigorous, and more accurate assessments of biodiversity.