Effects of egg removal on maternal aggression, biogenic amines, and stress indicators in ovigerous lobsters (Homarus americanus)

Abstract

In many disparate taxa, including crayfish, a freshwater decapod crustacean, the presence of one’s offspring has been shown to be an important variable in the level of maternal aggression. Ovigerous American lobsters (Homarus americanus) show a territorial advantage against nonmaternal females, even though no posthatch care is provided. The eggs are attached to the pleopods (swimmerets) throughout embryogenesis. We evaluated the effect of stripping ovigerous H. americanus females of their eggs on maternal territoriality. In one treatment group, maternal females were stripped of all eggs. Twelve days later, including being individually isolated for an additional 48 h in a test tank, each resident was serially intruded upon by 4 non-maternal conspecific females. An identically treated control group of ovigerous female residents was left intact prior to the serial intrusions. Various biochemical parameters of the stripped and unstripped animals were measured before and after the experimental treatment (or control). The behavioral modulators measured were the biogenic amines, octopamine and serotonin, and the stress indicators were a heat-shock protein (HSP70), methyl farnesoate, and crustacean hyperglycemic hormone. The intact ovigerous residents showed a significant territorial advantage over the intruders, whereas the contest outcomes of stripped residents were reduced to chance. The presence of eggs in maternal H. americanus is therefore necessary for the maintenance of the shelter-related territorial advantage. However, no significant differences in any of the biochemical parameters were observed between or within treatment conditions. It appears that these amines are not prominently involved in the mechanism of maternal aggression, and that these changes in territorial defense are not simply due to changes in general stress as a result of stripping the females of their eggs.

Keywords:

• Lobsters
• Maternal aggression
• Territoriality
• Serotonin (5-HT)
• Octopamine
• Biogenic amines

Acknowledgments

We thank S.A. Chang for laboratory and editing assistance, W.A. Hertz for laboratory assistance, R. Johnson (Center for Molecular Neurosciences, Vanderbilt University) for quantification of the amines, and M. Syslo (Massachusetts State Lobster Hatchery and Research Station) for ovigerous lobsters. This article was funded in part by grants from the National Sea Grant College System, National Oceanic and Atmospheric Administration, U.S. Department of Commerce, under grant number R/A-108, project number NA66RG0477, through the California Sea Grant College system and in part by the California State Resources Agency, and grant LR/LR-1 through the Connecticut Sea Grant College system. The views expressed herein are those of the authors and do not necessarily reflect the views of NOAA or any of its subagencies. The U.S. Government is authorized to reproduce and distribute for governmental purposes.