Phylogeny and evolution of large body size in the rove beetle genus Phlaeopterus Motschulsky, 1853 (Coleoptera: Staphylinidae: Omaliinae: Anthophagini)

Abstract

Abstract The omaliine rove beetle genus Phlaeopterus Motschulsky, 1853 contains 22 species. The genus is distributed across northwestern North America and eastern Asia. These beetles occur primarily along the edges of alpine snowfields and streams, habitats that are particularly sensitive to the impacts of climate change. Two species have not been collected since 1979 and 1984, one of which, Phlaeopterus bakerensis Mullen and Campbell, 2018, is a contender for the largest-bodied species among the over 1,600 species of the subfamily Omaliinae. Here, we present the first phylogeny of the genus, using Bayesian and maximum likelihood analyses based on DNA sequences from the mitochondrial gene COI and morphological data. We tested previous taxonomic hypotheses and most were rejected by all three analyses. Phlaeopterus castaneus Casey, 1893 is non-monophyletic based on COI sequences and may have hybridized with P. loganensis Hatch, 1957. We found support for the monophyly of the genus Phlaeopterus. Our analyses suggest the common ancestor of the genus had small-bodied adults (maximum body size under 5 mm) with ocelli. Within this small-bodied radiation of species, ocelli were lost once and there were two separate evolutionary transitions to large-bodied adults. Although all the large-bodied species are snowfield-associated and only 25% of the small-bodied species are, we did not find statistical support for a relationship between large body size and use of snowfield habitats. These findings represent the first modern phylogenetic reconstruction of species-level relationships within the rove beetle subfamily Omaliinae using both morphological and molecular data.