Uncovering cryptic diversity in the enigmatic ant genus Overbeckia and insights into the phylogeny of Camponotini (Hymenoptera : Formicidae : Formicinae)

Many tropical insect species remain formally undescribed, and the validity of some rarely collected and poorly studied taxa is uncertain. Overbeckia Viehmeyer, 1916 is a monotypic ant genus and a rare member of the arboreal ant communities of tropical South East Asia and Australasia. Overbeckia subclavata Viehmeyer, 1916 was collected and described from Singapore more than a century ago and there have been few other records of these ants since. Here we compare the existing Overbeckia records with recent collections in Australia, New Guinea and Indonesia. We revise the taxonomic diagnosis of the genus Overbeckia in comparison with other genera of the diverse tribe Camponotini, redescribe O. subclavata and describe two new species, Overbeckia papuana sp. nov., and Overbeckia jambiensis, sp. nov. We also summarise all available ecological and distributional information of the genus, indicating that Overbeckia occurs in a variety of lowland vegetation types, from rainforests to secondary growth and plantations but is extremely rare. Using external morphological characters, internal proventricular structures and a molecular phylogeny of 78 Camponotini species based on five protein-coding loci, we demonstrate that Overbeckia is a monophyletic lineage. Molecular-clock calibrated trees using 21 fossil records indicate that the divergence between Overbeckia and its sister clade comprising the genera Echinopla Smith, 1857 and Calomyrmex Emery, 1895 occurred c. 21 Ma (95% highest posterior density 14-28), and that the divergence between the three Overbeckia species likely occurred in the late Miocene and Pliocene. In addition, we transfer one Camponotus Mayr, 1861 species to Colobopsis in the light of molecular evidence: Colobopsis triangulata (Klimes & McArthur, 2014) comb. nov. Our analysis represents the most comprehensive phylogeny of the tribe Camponotini in terms of coverage of extant divergent lineages, including Overbeckia, and suggests relatively robust phylogenetic relationships among genera that are consistent with published phylogenomic trees. Overall, our study reveals cryptic species diversity in Overbeckia and provides strong evidence that this is a valid and polytypic ant genus.