New findings on the sperm ultrastructure of Carabidae (Insecta, Coleoptera)

The sperm structure of several species belonging to different tribes of the large Carabidae family is described. Some species of Nebriinae, such as Nebria brevicollis and Notiophilus biguttatus, have free conventional insect sperm. Their sperm type can be regarded as the ancestral model for Carabidae. All the other species examined, either with isolated sperm such as Calomera nemoralis, Scarites sp., Duvalius andreinii and Anillus florentinus or with spermatozeugmata and sperm associated to spermatostyles such as Typhloreicheia usslaubi, Brachinus italicus, Carabus convexus, Calathus fuscipes, Calathus montivagus, and Paraphorus mendax, showed sperm with long nucleus and a parallel axoneme running the length of the tail starting from the apical bell-like acrosome. C. nemoralis, like Cicindela campestris previously studied, has a sperm structure similar to that of several other Carabidae, confirming their correct assignment to the family. C. convexus has the same sperm structure as previously studied C. preslii and C. interstitialis, indicating that the spermatozeugmata of the group consist only of an apical cap in which the anterior sperm regions are embedded. Unlike other Carabidae with spermatozeugmata, Carabini have the typical sperm organization with acrosome, nucleus and flagellum in a regular sequence. A. florentinus, (Trechinae) shows major differences, such as the absence of an acrosome and an extremely long nucleus that reaches the end of the tail in close association with the axoneme. T. usslaubi (Scaritinae) has slender spermatozeugmata with orderly quartets of sperm. The posterior region of the sperm tail is also unusual, showing a perfect circular section and a plasma membrane reinforced by a dense underlying layer. The present observations confirm that spermatozeugmata, can vary in shape and size among different species of the Carabidae. Such diversity may be the result of the male reproductive strategy, different in each species, that enhances the efficiency of sperm transfer to the female.