Genital structure, sperm competition and reproductive behaviour in some African libellulid dragonflies

The structure of the penis (vesica spermalis) and of the female genital tract are described in two African libellulids. The 4th segment of the penis of Brachythemis lacustris possesses a flagellum and paired cornua which are retracted inside a specialized chamber at rest. On inflation they are shot abruptly out of the chamber, and the flagellum is seen to possess a pair of large barbs while the cornua have complex laterally- and proximally-directed bristles. The female genital tract has an asymmetrically disposed spermathecal system which may permit the flagellum to reach only one spermatheca and withdraw sperm from it during copulation. In Nesciothemis farinosa the penis bears large inflatable sacs armed with numerous bristles some of which are serrated and dentate. In the female the spermathecae are inaccessible to the penis, but sperm from previous males may be packed down or removed from the bursa during copulation. B. lacustris copulates rapidly on the wing and the male guards the female closely during oviposition. N. farinosa also copulates rapidly but on the ground and guarding during oviposition is weak and short-lived. The possible relationships between copulation duration, intensity of guarding and sperm competition are discussed.