Keywords :
Behavioral constraints; Sex differences; Sexual differentiation; Testosterone; Vocal behavior; Gonadal Steroid Hormones; Animals; Female; Male; Gonadal Steroid Hormones/pharmacology; Testosterone/pharmacology; Brain; Sex Characteristics; Canaries/physiology; Vocalization, Animal/physiology; Canaries; Vocalization, Animal; Endocrinology; Endocrine and Autonomic Systems; Behavioral Neuroscience
Abstract :
[en] We previously confirmed that effects of testosterone (T) on singing activity and on the volume of brain song control nuclei are sexually differentiated in adult canaries: females are limited in their ability to respond to T as males do. Here we expand on these results by focusing on sex differences in the production and performance of trills, i.e., rapid repetitions of song elements. We analyzed >42,000 trills recorded over a period of 6 weeks from 3 groups of castrated males and 3 groups of photoregressed females that received Silastic™ implants filled with T, T plus estradiol or left empty as control. Effects of T on the number of trills, trill duration and percent of time spent trilling were all stronger in males than females. Irrespective of endocrine treatment, trill performance assessed by vocal deviations from the trill rate versus trill bandwidth trade-off was also higher in males than in females. Finally, inter-individual differences in syrinx mass were positively correlated with specific features of trills in males but not in females. Given that T increases syrinx mass and syrinx fiber diameter in males but not in females, these data indicate that sex differences in trilling behavior are related to sex differences in syrinx mass and syrinx muscle fiber diameter that cannot be fully suppressed by sex steroids in adulthood. Sexual differentiation of behavior thus reflects organization not only of the brain but also of peripheral structures.
Title :
Does the syrinx, a peripheral structure, constrain effects of sex steroids on behavioral sex reversal in adult canaries?
Funding text :
This work was supported by a Grant from the National Institute of Neurological Disorders and Stroke Grant RO1NS104008 (to G.F.B., J.B., and C.A.C.). We thank Pr. Robert Dooling and Ed. Smith, Department of Psychology, University of Maryland in College Park for providing the MATLAB script used to analyze canary song. C.A.C. is F.R.S.-FNRS Research Director.
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