In animals having internal fertilization, both sexes can potentially influence the post-copulatory processes
of sperm transfer, sperm storage and sperm use for fertilization. In this experiment, we investigated
whether Tribolium castaneum females can influence male paternity success following consecutive matings
with two different males. We compared second male paternity success (P2) between females exposed to
carbon dioxide (CO2) and control females kept in air, in both cases for 30 min between two matings.
CO2 exposure inhibits muscular activity and has previously been shown to decrease sperm storage by T.
castaneum females. Females exposed to CO2 after their first mating showed significantly higher P2 than
control females during the later portion of a one-month oviposition period. These results are consistent
with reduced storage of first male sperm by CO2-exposed females. Also, T. castaneum females showed
considerable variation in spermathecal morphology, and P2 decreased with increasing spermathecal tubule
volume. These results demonstrate that T. castaneum females can influence male paternity success, and
suggest that differential sperm storage may be an important mechanism of post-copulatory female choice.
Keywords: cryptic female choice; sperm precedence; spermathecal morphology; sexual selection