Thesis

Leg armaments and alternative mating behavior in Pristoceuthophilus camel crickets

In the animal kingdom, males of many species possess striking weaponry used in intrasexual competition for access to females. Until recently, there were no known cases of male weaponry being used against females in sexual coercion. However, in the camel cricket Pristoceuthophilus marmoratus, males use modified hind legs (modifications consist of femoral spines and bent tibiae) not only to fight with each other, but also to trap females and force them to copulate. As male hind leg armaments are positively allometric, the largest males would be best equipped to force-copulate, although they should be the most attractive to females. In order to resolve this potential paradox and determine which males are most likely to force-copulate, I manipulated male body size with diet and performed mating trials. The use of forced copulation was conditional on male body size, with smaller males being more likely to attempt coercive mating. The finding is in accord with the literature on male predictors of forced copulation and suggests an evolutionary exaptation of hind leg armaments in this species, wherein an intrasexual fighting weapon took on a secondary function of sexual coercion. In addition to this study, I performed a comparative survey of armaments, examining fighting and mating behavior in four morphologically similar congeners (P.'Huachuca summer,' P. arizonae, P.'Madera,' and P.'Mt. Pinos') to determine whether hind leg armaments also serve intra- and intersexual functions in these species. Intrasexual leg fighting occurred in all species for which trials were performed, while hints of sexual coercion occurred in two species (P.'Huachuca summer' and P.'Mt. Pinos'), suggesting additional cases of a uniquely dual-purpose armament.

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