Ethological concepts revisited: Immediate early gene induction in responseto sexual stimuli in birds

Courtship behaviors were interpreted by ethologists as being examples of 's ign stimuli' that would act as 'releasers' of stereotypic species-typical b ehaviors in conspecifics. A key component of the sign stimulus concept is t hat some form of stimulus filtering occurs that is responsible for the mark ed selective behavioral responsiveness. Studies of immediate early gene ind uction in the avian brain in response to conspecific stimuli associated wit h courtship and mating reveal that such gene induction is highly selective. In male Japanese quail (Cotumix japonica), studies of the immediate early gene c-fos or zenk have been conducted in birds engaging in both appetitive and consummatory aspects of male sexual behavior. High induction of immedi ate early genes occurs in hypothalamic and limbic areas such as the medial preoptic nucleus, bed nucleus striae terminalis and parts of the archistria tum in birds who had copulated and/or who had expressed a learned social pr oximity response, reflecting appetitive sexual behavior. Immediate early ge ne expression was also increased in telencephalic areas such as the hyperst riatum ventrale that presumably plays a role in the integration of sensory cues related to female recognition. In European starlings, studies of zenk induction have been conducted in females who hear male-typical courtship so ng. Clayton and Mello had shown that zenk is induced in the auditory telenc ephalon of canaries and zebra finches at high levels specifically in respon se to conspecific song. Immediate early genes such as fos and zenk are also expressed in song control nuclei specifically in association with song pro duction. In starlings it was found that song was effective in rapidly induc ing zenk expression in the auditory telencephalon in males and in females i n the breeding as well as in the nonbreeding season. Thus, the expression i s not greater in females who use song to choose mates or during the breedin g season when females are choosing mates. However, there is evidence that h igh levels of induction in certain areas of the auditory telencephalon in f emales are greater in response to songs organized in longer bouts that fema les prefer. Though immediate early gene induction in the brain does not exa ctly mimic selective behavioral responses to sign stimuli it may represent one important way in which stimulus selectivity of the sort hypothesized pr eviously by Tinbergen and Lorenz is coded. Engaging in species-typical beha viors is also associated with motor-driven immediate early gene expression. Copyright (C) 2001 S. Karger AG, Basel.