SPERM MIXING IN THE COCKROACH DIPLOPTERA PUNCTATA

Females of the viviparous cockroach Diploptera punctata store sperm from their first mating, and do not remate until after giving birth to their first batch of young. The irradiated male technique was used to determine the outcome of sperm competition in the second batch of eggs of females mated sequentially to normal and irradiated males. It is estimated that the second male to mate with a female fertilizes approximately two thirds of the eggs in a female's second batch of eggs. Direct evidence for sperm mixing was obtained. Undeveloped eggs (fertilized by irradiated sperm) and developing embryos (fertilized by normal sperm) were found interspersed throughout oothecae that were extruded from females, demonstrating that normal and irradiated sperm were released from the spermathecae at oviposition and that they competed for fertilizations.