Reinventing the spermatheca: unveiling a novel sperm storage organ in Epilachninae ladybirds.

Abstract

This study investigates the reproductive apparatus of Epilachna clandestina, focusing on its secondary spermatheca, first described as a 'seminal node' by Katakura et al. for the Asian Epilachninae. We corroborate their previous findings that highlight this organ as the primary sperm storage site, contrasting with a vestigial typical spermatheca that lacks significant functionality. The functional spermatheca is a dilated, secretory region of the common oviduct filled with sperm. It features a specialized epithelium containing class 3 secretory cells and is lined by a thin chitinous cuticle, indicating that it qualifies as a true spermatheca. This organ seems to optimize sperm storage and maintenance when compared to the vestigial spermatheca. Additionally, we emphasize the close association between sperm and epithelial structures as mechanisms for efficient sperm retention and dosage, which could quantitatively and qualitatively improve reproductive success. Our findings may contribute to a greater understanding of the evolutionary adaptations of reproductive structures in Epilachninae and raise questions regarding the evolutionary history of these organs within ladybirds.