Spermiogenesis and sperm dimorphism in Edessa meditabunda (Fabricius, 1794): Emphasis on aberrant sperm structure and its systematic implications for Edessinae.

Sperm heteromorphism is widespread in Pentatomidae and has been reported in other Heteroptera species. However, its developmental origins and morphological diversification remain poorly characterized, as is the case in the subfamily Edessinae. To advance these issues, we characterize spermiogenesis and sperm dimorphism in Edessa meditabunda (Fabricius, 1794), using light, scanning, and transmission electron microscopy. The testes of E. meditabunda contain four elongated follicles, positioned in parallel. In all four follicles, spermiogenesis follows a similar sequence but diverges markedly in its final organization. Three follicles (1, 2, and 3) produce typical spermatozoa, whereas the fourth follicle forms exclusively aberrant spermatozoa. Typical spermatozoa are elongated, measuring 314 µm in total length and 29 µm in the nucleus. They exhibit conserved heteropteran characteristics, such as a "half-moon-shaped" mitochondrial derivatives connected to the axoneme by bridges, and absence of accessory bodies. In contrast, the aberrant spermatozoa have a total length of 122 µm and a nucleus of 73 µm. This morphotype exhibits pronounced deviations in the acrosome, nuclear enlargement, and highly dilated mitochondrial derivatives that surround the axoneme completely. To date, these features make the aberrant sperm of E. meditabunda one of the most atypical morphologies described for Pentatomidae and expand the range of characters available for comparison within Edessa, offering a powerful tool to refine species boundaries and improve the systematic resolution of the genus. These findings shed light on sperm dimorphism in Edessinae, support interpretations of aberrant sperm, and demonstrate the systematic value of sperm ultrastructure in this group.