Forceps size does not determine fighting success in European earwigs

Male European earwigs (Forficula auricularia) posses substantially larger f orceps than females and use these forceps to batter rivals in intrasexual c ontests to determine dominance. Although previous investigations have shown that male fighting and mating success increases with forceps size, it is n ot clear that sexual selection acts directly on forceps size per se; increa sed forceps size may be a correlated response to selection for some other t rait. We experimentally reduced forceps length of males and paired them wit h unmanipulated males in staged encounters. Although apparent (postmanipula tion) forceps length did not affect contest outcomes, original (premanipula tion) forceps length did: males with longer original forceps won more conte sts. These results suggest that weapon size itself does not determine succe ss in contests between male European earwigs. Thus, sexual selection may op erate on forceps size in some other context or may act on some other trait that covaries with forceps size.