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 Monomorium 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 M. brachypterum sp. nov. 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 M. intrudens. Within their overlapping distributions, analyses based on partial sequences of the mitochondrial COI gene showed that the two species are phylogenetically distinct. The queens of M. brachypterum are distinguished from those of M. intrudens by degenerated wings, suggesting contrasting dispersal strategies between the two sister species. In addition, a phylogenetic analysis performed for the Japanese Monomorium 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.