title: Heightened serotonin influences contest outcome and enhances expression of high-intensity aggressive behaviors.
abstract: The outcome of behavioral interactions between organisms can have significant fitness implications. Therefore, it is of great theoretical and practical importance to understand the mechanisms that modify different agonistic behaviors. Changes in central monoamines, such as serotonin (5-HT), contribute to modifying the expression of aggressive encounters in both vertebrates and invertebrates. In several invertebrate groups, neural 5-HT has been linked to heightened aggression and conflict escalation. The male stalk-eyed fly (Teleopsis dalmanni) competes with conspecifics daily over access to resources such as food and mates. Because encounters escalate in a stereotypical manner, stalk-eyed flies provide an excellent model system to study behavioral syndromes. We hypothesized that noninvasive, pharmacological augmentation of brain 5-HT by administration of the precursor, 5-hydroxytryptophan (5-HTP), would increase stereotypic behavioral escalation and the probability of winning a conflict over food. Size-matched male 5-HTP-treated and untreated flies were placed in a forced-fight paradigm and their aggressive behaviors scored. Individuals with higher brain 5-HT levels had a markedly higher probability of winning the contests, displayed greater levels of high-intensity aggressive behaviors and fewer retreats. Pretreatment with 5-HTP did not significantly alter octopamine or tyramine, suggesting that central 5-HT may modulate aggression in these organisms and play a role in determining reproductive success and resource attainment.
authors.affiliation: Neuroscience Program, University of Colorado-Denver Anschutz Medical Campus, Aurora, CO 80045, USA. Electronic address: Andrew.Bubak@UCDENVER.EDU.
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Bubak
authors.affiliation: Department of Biology, University of South Dakota, Vermillion, SD 57069, USA.
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Renner
authors.affiliation: Department of Integrative Biology, University of Colorado-Denver, Denver, CO 80217, USA.
authors.forename: John G
authors.initials: JG
authors.lastname: Swallow
mesh_terms: D006916:5-Hydroxytryptophan / Q000494:pharmacology; D000374:Aggression / Q000187:drug effects / Q000502:physiology*; D000378:Agonistic Behavior / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D018687:Antidepressive Agents, Second-Generation / Q000494:pharmacology; D004175:Diptera; D004298:Dopamine / Q000378:metabolism; D005426:Flight, Animal / Q000187:drug effects; D008297:Male; D009655:Octopamine / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism*; D014439:Tyramine / Q000378:metabolism
chemical_list: D018687:Antidepressive Agents, Second-Generation; D009655:Octopamine; D012701:Serotonin; D006916:5-Hydroxytryptophan; D004298:Dopamine; D014439:Tyramine
keywords: 5-Hydroxytryptophan; Aggression; HPLC; Invertebrate; Serotonin; Stalk-eyed fly