The first analysis of the sperm ultrastructure of Mycetophagidae, Tetratomidae, and mycetophagous Tenebrionidae (Coleoptera: Tenebrionoidea)

Tenebrionoidea, a diverse beetle superfamily, exhibits complex and poorly resolved phylogenetic relationships. Sperm ultrastructure varies notably among its families, yet many remain unstudied. Here we examined for the first time the sperm morphology in four species from the families Mycetophagidae, Tetratomidae, and Tenebrionidae using ultrastructural techniques. We observed a consistent antiparallel arrangement of spermatids or spermatozoa in the germ cysts and documented significant interspecific differences in acrosome and nucleus dimensions. Flagellar analyses revealed asymmetrical mitochondrial derivatives and an unprecedented tail-end microtubule arrangement. These findings refine species identification and enhance understanding of reproductive morphology within Tenebrionoidea. Our results underscore the utility of sperm ultrastructure as a taxonomic and phylogenetic tool, highlighting its potential to clarify evolutionary relationships in this complex group, while also indicating the necessity for further studies encompassing additional species.