Photoperiodic Changes in Aggression

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Most animals experience large fluctuations in environmental conditions across the seasons of the year. Consequently, many animals display seasonal changes in physiology and behavior which allow them to cope with seasonal changes. Day length is the main environmental cue used by animals to coordinate seasonal behavioral and physiological responses. For example, animals living in long "summer-like" day lengths will maintain high levels of the hormone testosterone and thus will continue to breed, whereas animals housed on short "winter-like" days will inhibit their breeding due to low testosterone. In addition, it has recently been demonstrated that rodents housed in short days display increased aggression compared with animals housed on long days, despite lower levels of testosterone. This finding is particularly interesting given the traditional belief that testosterone regulates aggression. This project is designed to investigate the hormonal mechanisms regulating seasonal changes in aggression in rodents. Specifically, animals will be housed in long or short days in the lab and levels of specific hormones, including testosterone and the adrenal hormone cortisol, will be experimentally manipulated. Aggression will then be videotaped and quantified using a computer-based video analysis system. Based on previous research, it is predicted that the adrenal hormone cortisol, rather than testosterone, regulates seasonal aggression. These experiments challenge the simple notion that all forms of aggression are testosterone-dependent and have important implications for the study of how hormones act on the brain to regulate social behaviors and how these behaviors may be altered by the environment. Collectively, these studies will help identify important and novel mechanisms of hormonal control of aggression. Importantly, these studies will provide excellent opportunities for both graduate and undergraduate students, including under-represented minorities, to gain hands-on experience and to allow them to develop important scientific skills by conducting, presenting and publishing scientific research.