SEXUAL SELECTION AND SEXUAL DIMORPHISM IN THE HARLEQUIN BEETLE ACROCINUS-LONGIMANUS

To investigate the causes of striking sexual dimorphism in the harlequ in beetle (Acrocinus longimanus), we carried out a study of the behavi or and morphology of two widely separated populations (in French Guian a and Panama). Males of this species possess greatly elongated foreleg s which exhibit strong positive allometry with body size (elytra lengt h). Males use their forelegs in fights with other males and in guardin g females and oviposition sites. Field data on fighting and mating suc cess suggest that sexual selection favors large size in males. However , the direct targets of selection were masked by high correlation betw een traits of the elytra, forelegs, and antennae. Sexual selection app ears to be driven by intense male competition to monopolize suitable s ites for egg deposition. Female harlequin beetles are highly selective in choosing only recently dead or dying trees for oviposition (Morace ae and Apocynaceae). Despite marked geographic variation in coloration , host trees, and climate, the two populations did not differ in mean size and extent of sexual dimorphism. We suggest that sexual selection in this species is sufficiently intense to override any effects of di ffering ecological factors.