Sexual Selection and Sexual Dimorphism in the Harlequin Beetle Acrocinus longimanus

Abstract

To investigate the causes of striking sexual dimorphism in the harlequin beetle (Acrocinus longimanus), we carried out a study of the behavior and morphology of two widely separated populations (in French Guiana and Panama). Males of this species possess greatly elongated forelegs which exhibit strong positive dometry with body size (elytra length). Males use their forelegs in fights with other males and in guarding females and oviposition sites. Field data on fighting and mating success suggest that sexual selection favors large size in males. However, the direct targets of selection were masked by high correlations between traits of the elytra, forelegs, and antennae. Sexual selection appears to be driven by intense male competition to monopolize suitable sites for egg deposition. Female harlequin beetles are highly selective in choosing only recently dead or dying trees for oviposition (Moraceae and Apocynaceae). Despite marked geographic variation in coloration, host trees, and dimate, 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 differing ecological factors.

Diversity in the Weapons of Sexual Selection: Horn Evolution in the Beetle Genus Onthophagus (Coleoptera: Scarabaeidae)

“…Sexual selection is expected to continuously favor large weapon sizes (Parker 1979(Parker , 1983West Eberhard 1983;Andersson 1994), and horned beetles fit this pattern: in every species tested thus far, males with the longest horns won disproportionate access to females (Eberhard 1982;Goldsmith 1987;Siva-Jothy 1987;Zeh and Zeh 1992;Rasmussen 1994;Emlen 1997;Moczek and Emlen 2000). Yet, our phylogeny suggests that complete loss of all horns has occurred at least three times (branches leading to O. pennsylvannicus; to O. cochisus, O. coscineus, and O. knulli; and to O. muticus).…”

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“…This phoretic association has been reported more than a century ago (e.g. Ellingsen 1905), where the Harlequin beetle is the obligate dispersal agent of C. scorpioides (Zeh, Zeh & Tavakilian 1992;Zeh & Zeh 1994a, 1994b. Despite the wide distribution of this beetle species across the Neotropics, little is known about the distribution of this phenomenon (e.g.…”

Population-specific DNA fingerprints in a neotropical pseudoscorpion (Cordylochernes scorpioides)

“…Although the populations from French Guiana and Panama experience markedly different climates and microhabitats (Zeh et a!., 1992), we have found that they share a complex set of behaviours associated with dispersal and male competition. The pseudoscorpion disperses from old to newly dead or dying trees under the elytra of the giant harlequin beetle, Acrocinus longimanus (Zeh & Zeh, 1992a,b, Zeh eta!., 1992.…”