The Role of Octopamine in Male Cricket Aggression
Prof. Hadley Horch
Bowdon College Department of Neurobiology
Male crickets serve as a model organism for the study of aggression in invertebrates. Aggression is displayed through fights that escalate through a predictable, easily quantified, step-wise progression with a clear winner and loser. Previous research has described the importance and influence of each of these steps on the outcome of an encounter. Particularly, the duration of antennal fencing and the use of mandible engagement have been correlated to the overall intensity of the encounter and each crickets willingness to fight (Hofmann and Schildberger 2000). With the progression of a fight so extensively documented and the relatively simplistic neural systems that underlie this behavior, research can now be focused on attempting to influence the outcomes of these fights using specific chemicals that alter the properties of neurons involved. Specifically, we are studying the effects of octopamine and determining if it alters these aggressive behaviors.
Octopamine is a biogenic monoamine whose pathway in invertebrates is homologous to the adrenaline pathway in vertebrates. After extended periods of activity, including fighting, levels of octopamine in the heamolymph are elevated (Adamo et al. 1995). We hypothesize that by administrating an injection of octopamine to a cricket that has lost a series of fights to the same partner, we can turn a subordinate cricket into a dominant cricket. Several aspects of the fight sequence will be measured to determine if the hierarchy can be reversed, and if octopamine will significantly alter the aspects such as the length of fight, or the overall intensity of the fight.
Crickets of the species Acheta domestica are paired by weight and fought for five consecutive days. Every day of the experiment, except for the fourth day, each cricket is injected with insect saline prior to being fought. One day four, the subordinate cricket of each pair is administered octopamine instead of saline. Observational data appears to show that the outcome of the fights do not change on the octopamine day but on the next day we found a reversal of approximately half of the hierarchies. The video analysis of the specific aspects of the fights is still pending.