Neuroendocrine and behavioral response to testosterone-induced female song in canaries (Serinus canaria)

Abstract

Male song in songbirds is a critical and elaborate signal for mate attraction. In many species female listeners respond to male song both behaviorally and physiologically (e.g. copulation solicitation displays and production of the immediate early gene ZENK in auditory regions). It is becoming increasingly well known that females in many species also sing. However, in common lab species, such as canaries (Serinus canaria), female song is limited and has been primarily studied in the context of administering of exogenous testosterone (T) to increase song rate and length. In this study we addressed to what extent female canary songs are masculinized by the administration of exogenous T based on the behavioral and physiological responses of avian receivers. Specifically, are T induced female songs sufficient to elicit courtship behaviors and auditory ZENK expression in female listeners? We found that female songs after 3 weeks of exogenous T were significantly longer and more complex than female songs after 12 weeks of exogenous T. Additionally, we found that playback of 3-week T song significantly increased sexual response behaviors and the expression of ZENK in the auditory brain regions of female listeners. Finally, we conclude that extended periods of T do not necessarily maintain the masculinization of female song.

Keywords: Birdsong; Canary; Hormone; Immediate early gene; Trill rate; ZENK.

Figure 1.. Auditory brain regions.

Shown on a sagittal section, grey boxes indicate areas in which ZENK was quantified for each auditory brain region. Nidocaudal mesopallium (NCM (d:dorsal, v:ventral)); Caudomedial mesopallium (CMM).

Figure 2.. Female song spectrograms.

A) Female song exemplar after 3 weeks of exogenous T B) Female song exemplar after 12 weeks of T.

Figure 3.. Behavioral Responses.

Summary of sexual and general behavioral responses in response to each playback type. 3wkT songs induced more A. sexual behaviors (but not B. general behaviors) than silence.

Figure 4.. ZENK responses.

Summary of ZENK expression in each auditory brain region for each playback type. Nidocaudal mesopallium (NCM (d:dorsal, v:ventral)); Caudomedial mesopallium (CMM). *: p<0.05; **: p<0.001

Figure 5.. Example photomicrographs.

Exemplar images of ZENK expression in female listeners after listening to 3wkT female song or silence. Scale bar equals 50 μm. Nidocaudal mesopallium (NCM (d:dorsal, v:ventral)); Caudomedial mesopallium (CMM).