Female influence over offspring paternity in the red flour beetleTribolium castaneum

Abstract

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.