Male Dominance and Sexual Selection in the Crayfish Orconectes quinebaugensis

Warren, Amy H

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Male Dominance and Sexual Selection in the Crayfish Orconectes quinebaugensis

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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 sexual selection, allowing dominant males greater access to females, thereby increasing their reproductive success. This work tests the hypothesis that high male investment in dominance interactions may have evolved as a result of intra- and/or inter-sexual selection pressures by testing specific predictions in two parts: first, that reproductive males would invest more in agonistic interactions than reproductive females or non-reproductive members of both sexes; and second, that females would prefer odors of dominant males over subordinates, and that dominant males would be either more efficient at mating or be able to mate longer than subordinates. Investment in agonistic interactions was examined in intrasexual pairs of male and female crayfish in both the reproductive and non-reproductive season. As predicted, reproductive males invested more in agonistic interactions overall than reproductive females, while there was no significant difference in investment by non-reproductive males or females. However, no significant difference was found in agonistic investment between reproductive males and non-reproductive males. These data indicate that investment in agonism differs by sex and by reproductive status, and may indicate that dominance interactions are under sexual selection in males. Alternatively, this differential investment may be explained by seasonal changes in the individual costs and benefits of agonism, or by depressed investment by reproductive females. Female odor preference was tested using a y-maze containing control and male treated water. For tests of male mating, time spent in each of three stages of mating was recorded for male-female pairs. Of these tests, the only significant trend produced was that dominant males spent more time associated with the female during and after copulation than subordinates. This may indicate an advantage in fertilization success for males through decreased sperm competition. A pilot study was also conducted testing the predictions that females mated to dominant males invest more in offspring than those mated to subordinates and that such offspring have greater survivability, but no significant conclusions could be drawn from these data.

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