SEXUAL SELECTION AND THE ALLOMETRY OF EARWIG FORCEPS

Positive intraspecific allometry, the tendency for large individuals t o have relatively larger morphological traits, is thought to be more l ikely for secondary sexual traits than naturally selected traits. This is because secondary sexual traits are often used to signal individua l quality and positive allometry should arise where the costs and/or b enefits of signalling are size dependent. Here we examine the allometr ic relationships between forceps length, a sexually selected trait and elytra length, a naturally selected trait, in 42 species of earwig. B oth forceps and elytra showed positive allometry. However, the degree of allometry was greater for forceps as predicted. if allometry arises due to sexual selection we would predict a greater degree of allometr y in species with more exaggerated secondary sexual traits. Across spe cies, the degree of forcep allometry did increase with forcep exaggera tion. The relevance of positive allometry to reliable signalling is di scussed.