Phylogenomic analyses of rare Neotropical lineages reveal the independent loss of antennal rami in railroad-worm beetles (Coleoptera: Phengodidae)

Abstract Phengodidae, or railroad-worm beetles, are bioluminescent soft-bodied beetles with flight capable adult males and highly paedomorphic larviform females. They are well accepted as part of the “lampyroid” clade within Elateroidea, and their suprageneric relationships have been recently studied using a phylogenomic approach. However, the placement of taxa currently classified in the subfamily Penicillophorinae remained untested. Penicillophorinae form an assemblage of morphologically modified, rarely collected Neotropical genera that are unique among Phengodidae. They are particularly characterized by their moniliform, serrate or uniramose antennae, in contrast to the typically bipectinate antennae present in all other members of the family. To investigate the phylogenetic position of Penicillophorinae, we implemented a low-coverage whole genome sequencing approach to produce genomic data for Acladocera and Walterius , two out of five genera classified in this subfamily. The resulting phylogenomic analyses confirmed the monophyly of Phengodidae; however, Penicillophorinae were not found as a monophyletic group. Our results recovered the topology: Cydistinae + (Phengodinae + ( Acladocera + (Cenophenginae + Mastinocerinae including Walterius ))). Therefore, we suggest that the antennal double rami were lost at least twice among Phengodidae: once in the newly circumscribed Mastinocerinae (with Walterius ), and once in Acladocera , which we tentatively keep in Penicillophorinae. Further, we discuss the morphological modifications of other genera currently classified in Penicillophorinae. Future phylogenomic research should focus on clarifying the boundaries and composition of phengodid subfamilies, particularly by including additional genera from Penicillophorinae and Mastinocerinae.