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Title: Reproduction, dominance, and caste: endocrine profiles of queens and workers of the ant Harpegnathos saltator

item PENICK, CLINT - Arizona State University
item LIEBIG, JUERGEN - Arizona State University
item Brent, Colin

Submitted to: Journal of Comparative Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2011
Publication Date: 7/20/2011
Citation: Penick, C.A., Liebig, J., Brent, C.S. 2011. Reproduction, dominance, and caste: endocrine profiles of queens and workers of the ant Harpegnathos saltator. Journal of Comparative Physiology. 197(11):1063-1071.

Interpretive Summary: Social insect colonies have reproductive and non-reproductive members. The regulation of this division, and further task partitioning among non-reproductive workers is often under the control of two hormones, juvenile hormone (JH) and ecdysteroids. We measured these hormones in colony members of Harpegnathos saltator, an ant species in which true queens, reproductive workers and non-reproductive workers occur. Our comparisons revealed hormone levels were similar for all three forms. Furthermore, application of JH failed to induce egg production, which is atypical for most insects. In contrast, a comparison between workers that specialized on foraging outside the colony versus those specializing on inside tasks indicated significant hormonal differences. Together, these results support the hypothesis that the hormones normally involved in regulating reproductive function have been repurposed to control non-reproductive worker behaviors in H. saltator.

Technical Abstract: The regulation of reproduction within insect societies is a key component of the evolution of eusociality. Differential patterns of hormone expression often underlie the reproductive division of labor observed among colony members, and further task partitioning among workers is also often correlated with differences in juvenile hormone (JH) and ecdysteroid expression. We measured JH and ecdysteroids in workers and queens of the ant Harpegnathos saltator. In this species, new colonies are founded by a single queen, but after she dies workers compete in an elaborate dominance tournament to decide a new group of reproductives termed “gamergates.” Our comparisons revealed that queens, gamergates, and inside workers (non-reproductive) did not differ in levels of JH or ecdysteroids. However, increased JH and decreased ecdysteroid content was observed in outside workers exhibiting foraging behavior. Application of a JH analog to virgin queens of H. saltator, although effective at inducing dealation, failed to promote egg production. Together, these results support the hypothesis that JH has lost its reproductive function in H. saltator to regulate foraging among the worker caste.