Sperm precedence in the damselfly Ischnura senegalensis (Rambur): is prolonged copulation advantageous to sperm precedence? (Zygoptera: Coenagrionidae)

To understand the relationship between copulation duration and sperm precedence in I. senegalensis, which mate for several hours, laboratory experiments and field observation were conducted. By irradiated male techniques, P2 value (sperm precedence of the last male to mate) was measured. P2 value was almost 100 % until 2 days after copulations regardless of the copulation duration. The interval between copulations in a $ was about 2.3 days in the field. It is suggested that the last <J to mate gains advantages in sperm precedence regardless of the copulation duration in the field. And complete sperm mixing (the point when the P2 value was 50 %) occurred 6 days after copulation.