Patterns of sperm use in the scorpionfly Panorpa germanica L. (Mecoptera: Panorpidae)

摘要

Sperm competition can be a powerful selective force in the evolution of reproductive strategies and mating systems. In studies on sperm competition, patterns of sperm use are typically reported as the mean species value of P sub(2), determined as the proportion of offspring sired by the second male to copulate with a doubly mated female. However, the within-species variance in P sub(2) has mostly been ignored, although taking this variance into account may be crucial for understanding the underlying mechanisms of sperm competition. Paternity analysis among the offspring of doubly mated females of Panorpa germanica (Mecoptera, Panorpidae) revealed a relationship between relative copulation durations of both males and the proportion of offspring each male will sire. This correlation between proportional copulation durations and paternity suggests mixing of sperm from different males inside the female's spermatheca. Yet, sperm mixing appears to be incomplete, as paternity was overall slightly shifted towards the second male on average fathering a higher proportion of the offspring than its relative copulation duration would predict in case of complete sperm mixing. For individual males, however, the outcome of sperm competition is rather unpredictable as the intraspecific variance in P sub(2) was found to be very high, irrespective of copulation durations. Possible causes of the observed variance in P sub(2) and the partial last male sperm precedence are discussed.