Structural and ultrastructural characterization of the spermatozoa in Pachycondyla striata and P. marginata

Abstract

This study characterizes the male gametic cells in two ant species (Pachycondyla striata and Pachnoda marginata) by light and transmission electron microscopies. The sperm of both species is composed of head, flagellum, and transition regions. The head consists of the acrosome, tapered and bilayer, and a cylindrical nucleus. In P. marginata, the intranuclear material is homogeneously compacted, and in P. striata, there are translucent inclusions and density variations. In the transition region of both species, centriolar adjunct, nuclear base, and the modified basal body (structure of the spermatozoa equivalent to the spermatids’ centriole) coexist and are progressively replaced by two oval and symmetrical mitochondrial derivatives and an axoneme 9 + 9 + 2, respectively, in addition to two symmetrical triangular accessory bodies. Moreover, cytochemical analysis with Ethanolic Phosphotungstic Acid Method (E-PTA) revealed species-specific features not previously reported in the Formicidae, such as the presence of E-PTA negative acrosomal vesicle, E-PTA positive perforatorium, and E-PTA positive nucleus, all in P. marginata. Mitochondrial derivatives exhibited distinct behavior in its internal composition, with E-PTA negative mitochondrial cristae and E-PTA positive paracrystalline in both species. Sperm morphology in Pachycondyla has marked morphological similarities with other ant groups, and its specific features can be useful tools to understand phylogenetic relationships within the Formicidae and Hymenoptera.