In many taxa, social structures are mediated by agonistic interactions and the formation of dominance hierarchies. In crayfish, dominance hierarchies may have evolved as a result of sexual selection, allowing dominant males greater access to females. We examine strategies of investment in agonistic behaviors for males and females of the crayfish Orconectes quinebaugensis in both the reproductive and non-reproductive seasons. We hypothesized that reproductive males would invest more in agonistic behaviors than reproductive females and non-reproductive crayfish. We tested this hypothesis in the laboratory with 4 treatment groups: males and females in the autumn reproductive season and males and females in the summer non-reproductive season, with each group subdivided by size to control for size effects. As predicted, reproductive males spent significantly more time in agonistic behaviors and had significantly more fights reaching maximum intensity than reproductive females, while there was no significant difference in the time spent in agonistic interactions by non-reproductive males or females. We did find that small females in the summer had significantly fewer fights reaching maximum intensity than either males or large females in the summer. However, there was no significant difference in time spent in agonistic interactions or proportion of fights reaching maximum intensity between reproductive males and non-reproductive males, as was predicted by our hypothesis. We did observe a significant effect of size for both males and females in the non-reproductive season, with larger animals spending more time in agonistic behaviors, and with large females having a more fights at maximum intensity than small females; this difference was not recapitulated in the reproductive season. These data indicate that investment in agonism differs by sex and by reproductive status, and the differential investment by sex in reproductive animals may indicate that dominance interactions are under sexual selection in males. However, high investment in agonism by both males and females in the non-reproductive season is not consistent with our hypothesis. Alternatively, the differential investment in agonism by reproductive males and females could be explained by either seasonal changes in the individual costs and benefits of agonism, or by depressed investment by reproductive females.