A new species of Monomorium Mayr, 1855 (Hymenoptera, Formicidae) with a brachypterous queen from southern Japan, and phylogeny of Japanese Monomorium species with diverse reproductive strategies

The genus <i>Monomorium</i> is an important phylogenetic group, notable for its taxonomic complexity and the presence of several well-known tramp species. In this study, we present a description of <i>M. brachypterum</i> <b>sp. nov.</b> from southern Japan along with an updated key to the Japanese species of the genus based on the worker caste. Molecular phylogenetic analysis using 13 protein-coding genes of the mitochondrial genome indicated that this new species is most closely related to <i>M. intrudens</i>. Within their overlapping distributions, analyses based on partial sequences of the mitochondrial <i>COI</i> gene showed that the two species are phylogenetically distinct. The queens of <i>M. brachypterum</i> are distinguished from those of <i>M. intrudens</i> by degenerated wings, suggesting contrasting dispersal strategies between the two sister species. In addition, a phylogenetic analysis performed for the Japanese <i>Monomorium</i> species provides support for the repeated evolution of diverse reproductive systems within this genus. The present study highlights a wide variety of evolutionary trends in the nest-level reproductive system, even among closely related species.