Sexual Selection for Male Mobility in a Giant Insect with Female‐Biased Size Dimorphism

• Published in: The American naturalist Vol. 172; no. 3; pp. 417 - 423
• Main Authors: Kelly, Clint D., Bussière, Luc F., Gwynne, Darryl T.
• Format: Journal Article
• Language: English
• Published: Chicago, IL The University of Chicago Press 01-09-2008; University of Chicago Press; University of Chicago, acting through its Press
• Subjects: Animal and plant ecology; Animal behavior; Animal, plant and microbial ecology; Animals; Biological and medical sciences; Biotelemetry; Body Size; Fecundity; Female; Female animals; Flowers & plants; Fundamental and applied biological sciences. Psychology; General aspects; Insecta; Insects; Insemination; Invertebrates; Locomotion; Male; Male animals; Mating behavior; Natural History Note; Nonnative species; Orthoptera - anatomy & histology; Orthoptera - genetics; Polymorphism; Reproductive success; Rugosa; Selection, Genetic; Sex Characteristics; Sexual Behavior, Animal; Sexual dimorphism; Sexual selection; Spermatophores; mobility; opportunity for sexual selection; Imates; sexual size dimorphism; sexual selection; Sexual selection; Biological evolution; Insecta; Mobility; Male; Breeding behavior; Arthropoda; Female; Sexual dimorphism; Invertebrata
• ISSN: 0003-0147; 1537-5323
• DOI: 10.1086/589894

Female‐biased size dimorphism, in which females are larger than males, is prevalent in many animals. Several hypotheses have been developed to explain this pattern of dimorphism. One of these hypotheses, the mobility hypothesis, suggests that female‐biased size dimorphism arises because smaller males are favored in scramble competition for mates. Using radiotelemetry, we assessed the mobility hypothesis in the Cook Strait giant weta (Deinacrida rugosa), a species with strong female‐biased size dimorphism, and tested the prediction that male traits promoting mobility (i.e., longer legs, smaller bodies) are useful in scramble competition for mates and thus promote reproductive success. Our predictions were supported: males with longer legs and smaller bodies exhibited greater mobility (daily linear displacement when not mating), and more mobile males had greater insemination success. No phenotypic traits predicted female mobility or insemination success. In species with female‐biased size dimorphism, sexual selection on males is often considered to be weak compared to species in which males are large or possess weaponry. We found that male giant weta experience sexual selection intensities on par with males of a closely related harem‐defending polygynous species, likely because of strong scramble competition with other males.