Revealing species diversity of Tomocerus ocreatus complex (Collembola: Tomoceridae): Integrative species delimitation and evaluation of taxonomic characters

Abstract

Tomocerus ocreatus species complex is among the commonest groups of Tomoceridae in East Asia and mainly distributed in the southern areas of China. Previous multi-locus molecular analyses have proved its monophyly and revealed extensive cryptic diversity within the complex. However, members of the complex are highly similar in traditional characters, thus morphological diagnosis have not been sufficiently developed in line with the molecular species delimitation. To update the taxonomy of the ocreatus complex, we carried out a molecular-morphological integrative study based on a wide-range survey of the complex in China. In addition to previous molecular analyses, we applied both distance and evolutionary model based methods on an enriched dataset of mitochondrial cytochrome c oxidase subunit I (COI) sequences. The molecular delimitation detected 20-36 molecular operational taxonomic units (MOTUs). In comparison, preliminary diagnosis based on traditional taxonomic characters distinguished only four morphological forms, while the characters previously thought to represent intraspecific variation distinguished 13 forms. According to a set of species validation criteria, the identities of nine independent species were acknowledged. Five new species: Tomocerus huangi sp.n., Tomocerus pseudocreatus sp.n., Tomocerus virgatus sp.n., Tomocerus yueluensis sp.n., and Tomocerus zhuque sp.n. are described, while Tomocerus changbaishanensis, Tomocerus spinulus and Tomocerus zayuensis are redescribed on the basis of holotype and/or topotypes. A key to the species of ocreatus-type tomocerids is provided. Incongruence across delimitation methods may be caused by incomplete sampling of populations and limitations of each method. The dorsal chaetotaxy, the prominent manubrial chaetae and the detailed morphology of dental spines were reviewed and confirmed to be valuable in the taxonomy of Tomocerus. The extensive diversity of the ocreatus complex in the southern areas of China indicates that tomocerid Collembola have much higher species richness than expected in the oriental realm. This study narrows species boundaries within the ocreatus complex and provides an example of how molecular approaches and detailed morphological examination can jointly benefit the exploration of biodiversity and the taxonomy of morphologically conservative groups of Collembola.