To understand the variation in aggressiveness and factors important for contest outcome, we quantified and compared agonistic interactions of four field cricket species in eastern North America: Gryllus fultoni (Orthoptera; Gryllidae), G. vernalis, G. pennsylvanicus, and G. rubens. The most aggressive behavior that we observed, the grapple, was frequently displayed in agonistic trials of G. pennsylvanicus and G. rubens. By contrast, we never observed this behavior in trials involving G. fultoni and G. vernalis. Consequently, species was the only significant variable affecting the variation in aggressiveness, whereas size difference, age difference, and contest duration had no significant effect. In species with high levels of aggressiveness, G. pennsylvanicus and G. rubens, the factors that might be indicative of resource holding potential such as size or age difference seemed to be significant for contest outcome. In species with low levels of aggressiveness, G. fultoni and G. vernalis, however, there were indications that contest outcomes were determined by aggressiveness itself rather than the size and age differences between opponents. Markov chain analyses revealed that the difference in aggressiveness between species with high and low levels of aggressiveness lay in a sequence of escalating behaviors: antennal fencing, mandible flare, and grapple. The escalated state of aggressiveness characterized by this behavioral sequence in G. pennsylvanicus and G. rubens seems to be the ancestral state in the North American Gryllus phylogeny. We argue that the loss of a tendency to use burrows in G. fultoni and G. vernalis might be related to low levels of aggressiveness in these species.
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Acknowledgments We are grateful to Yoonju Cho for the video analyses, to Mathew Zack for the statistical analyses, and to Susan Lappan and David Weissman for the critical comments. This paper was greatly improved by the critical reviews of anonymous referees. This work was supported financially by the University of Missouri Life Sciences Mission Enhancement Postdoctoral Fellowship and the Brain Korea 21 to YJ, by a U.S. National Science Foundation grant (IBN0091993) and a U.S. National Institute of Health grant (NIH R01 DC05760) to HCG, and by a Ewha Womans University research grant to JCC. The experiments in this study comply with the current law of the United States.
- Resource holding potential
- Resource value