Neural orchestration of mate-choice plasticity in songbirds

Females may choose between prospective mates based on signals that reflect male quality. In songbirds, variation in male song can be such a signal. Females can adjust their choosiness according to the prevalence of preferred song, presumably because environmental variation can influence the availability of preferred phenotypes. Studies using induction of the immediate early gene ZENK (also called zif-268, egr-1, NGFI-A, and Krox-24) as an indicator of neuronal activity have revealed that the caudomedial mesopallium (CMM) and caudomedial nidopallium (NCM) of the female auditory forebrain are sensitive to song quality and respond proportionally to the strength of the female's choosiness. In European starlings (Sturnus vulgaris), long songs are preferred by females and induce higher ZENK expression in the CMM and NCM compared to short songs. Experimentally reducing the perceived prevalence of long songs in the environment reduces this forebrain sensitivity to song length, raising the possibility that the songbird auditory forebrain integrates information about the social environment that enables the female to adjust her choosiness according to the availability of preferred phenotypes. In some songbird species, the noradrenergic system modulates mate-choice behavior, modulates song-induced auditory forebrain activity, and itself is modulated by the prevailing song environment, suggesting a possible role for this system in mediating the effects of social environment on forebrain and behavioral sensitivity to mate-choice cues. The presence of such a system would seem beneficial when the availability of preferred mates varies.