Divergent sperm traits in Carabidae ground beetles (Insecta: Coleoptera)

Sperm exhibit marked morphological diversity, and investigations into sperm diversity can further the understanding of many areas of evolutionary biology. In this study, using light microscopy, sperm morphology was examined in 39 species of Carabidae from eight subfamilies, including five subfamilies in which sperm morphology has not previously been examined. In all but one of the subfamilies, the subfamily members shared the same type of sperm: single sperm were observed in Cicindelinae, Nebriinae, and Trechinae; sperm conjugates, in which numerous sperm adhere together, were observed in Elaphrinae, Patrobinae, and Brachinae; and both single sperm and sperm conjugates were observed in Broscinae. In the remaining subfamily, Harpalinae, most species formed sperm conjugates, but some species formed single sperm. Some noteworthy sperm were also observed: the shortest single sperm in the order Coleoptera was found; multiflagellated sperm were observed, which had previously been reported from only one species in the class Insecta; and size variation of sperm conjugates, which may represent size dimorphism, was observed. Based on the results of this and previous studies, the evolutionary pattern of sperm traits and the phylogenetic utility of sperm morphologies in Carabidae are discussed.