Territorial Aggression and Dawn Song are Modulated by Septal Vasotocin and Vasoactive Intestinal Polypeptide in Male Field Sparrows (Spizella pusilla)

Abstract

Previous experiments demonstrate that lesions of the septum produce opposite effects on intraspecific male aggression in the territorial field sparrow (Spizella pusilla) and the colonial zebra finch (Taeniopygia guttata; facilitate vs inhibit, respectively) and intraseptal infusions of arginine vasotocin (AVT) and vasoactive intestinal polypeptide (VIP) modulate aggression in the male zebra finch (facilitate and inhibit, respectively). The present experiments were conducted to test the hypotheses that (1) septal AVT and VIP modulate both overt territorial aggression and the production of territorial song during the dawn chorus in male field sparrows and (2) these neuropeptides will exert effects opposite of those observed in the zebra finch, consistent with the prediction that social organization is associated with septal neuropeptide function. Wild-caught male field sparrows were fitted with chronic guide cannulae directed at the septum and were tested in outdoor aviaries placed in their natural habitat. Intrusion tests (introduction of a stimulus male) and dawn song observations were conducted following infusion of AVT, VIP, or saline control. Consistent with predictions, infusion of AVT significantly inhibited chases and significantly increased chase latency. No significant effects of VIP on chasing or chase latency were observed, although most subjects were more aggressive following infusion of VIP. Both AVT and VIP produced significant, selective effects on the complex (agonistic) song type (facilitation and inhibition, respectively) and produced no effect on the simple (multipurpose) song type. Thus, song and overt aggression appear be modulated independently by septal neuropeptides, and septal AVT and VIP function may differ between species which differ in the expression of territorial or colonial social organizations.