Sperm removal during copulation confirmed in the oldest extant damselfly, Hemiphlebia mirabilis

Postcopulatory sexual selection may favour mechanisms to reduce sperm competition, like physical sperm removal by males. To investigate the origin of sperm removal, I studied the reproductive behaviour and mechanisms of sperm competition in the only living member of the oldest damselfly family, Hemiphlebia mirabilis, one species that was considered extinct in the 1980s. This species displays scramble competition behaviour, whose males search for females with short flights and both sexes exhibit a conspicuous “abdominal flicking”. This behaviour is used by males during an elaborate precopulatory courtship, unique among the Odonata. Females use a similar display to reject male attempts to form tandem, but eventually signal receptivity by a particular body position. Males immobilise females during courtship using their legs, which, contrarily to other damselflies, never autotomize. Copulation is short (range 4.1-18.7 min), and has two stages. In the first stage, males remove part of the stored sperm, and inseminate during the second stage, at the end of mating. The examination of genitalia indicates that males have two horns covered by back-oriented spines, which match the size and form of female genitalia. The volume of sperm in females after copulation was 2.8 times larger than the volume stored in females whose copulation was interrupted at the end of stage I, indicative of a significant sperm removal. These results point out that sperm removal is an old character in the evolution of odonates, probably dating back to the Permian.