Handles for hosts: myrmecophilous adaptations in Chlamydopsinae (Coleoptera: Histeridae) revealed by behavioral and phylogenetic analyses, with description of a new Ceratohisteropsis species

The subfamily Chlamydopsinae (Coleoptera: Histeridae) represents one of the most specialized groups of ant-associated beetles, yet the function and evolutionary pattern of their elaborate cuticular modifications remain poorly known. Here, we describe a new species of the genus Ceratohisteropsis, collected from Tetramorium ant nests in Fujian, China. Field and laboratory natural history observations demonstrate that the beetle’s trident‑shaped pronotal carinae and associated ridges on the pronotum function as “handles,” facilitating passive transport by host workers. To place these findings in a broader evolutionary context, we present the first mitogenome-based phylogeny of the Histeridae. Our analyses yield an unstable placement of Chlamydopsinae within Histeridae, but with Saprininae frequently emerging as the sister group. The scattered distribution of myrmecophily across Histeridae, combined with the phylogenetic distances between obligate myrmecophilous lineages, suggests multiple independent origins of this lifestyle. Furthermore, revised morphology-based phylogenies indicate that the pronotal modifications found in Ceratohisteropsis are likely convergent adaptations in diverse forms across Chlamydopsinae. Our findings provide direct evidence that the characteristic surface relief of chlamydopsines, at least partly or in some cases, serves as a mechanical adaptation for ant‑mediated transport, offering new insight into the evolutionary mechanisms of beetle–ant symbiosis.