THE EFFECTS OF TESTICULAR TISSUE AND PREHATCHING INHIBITION OF ESTROGEN SYNTHESIS ON THE DEVELOPMENT OF COURTSHIP AND COPULATORY-BEHAVIOR IN ZEBRA FINCHES

As in many mammalian and avian species, testicular androgens or their metabolites activate courtship and copulatory behaviors in adult male zebra finches. However, studies of sexual differentiation of these beh aviors and related anatomical structures provide conflicting results. For example, posthatching estradiol can both masculinize courtship and the neural structures involved in song in females and inhibit the dev elopment of masculine copulation in males. These and other results hav e led to the hypotheses that (1) testicular androgens are converted to estradiol in the brain of developing males, and estradiol serves to m asculinize the song system, whereas (2) estradiol secretion by the fem ale ovary allows feminine rather than masculine copulatory behavior to develop. Treating embryonic zebra finches with the estrogen synthesis inhibitor fadrozole causes functional testicular tissue to develop in genetic females. The present study investigated the effects of such t reatment on the development of singing and copulatory behavior as well as song system anatomy in males and females. While exogenous testoste rone facilitated the display of sexual behaviors in adult males, the t esticular tissue in females had no masculinizing effect on the product ion of audible courtship song or copulation. Their song control nuclei were also not masculinized, even in individuals lacking ovarian tissu e. In contrast, embryonic inhibition of estrogen synthesis in males si gnificantly stimulated song production. These results suggest that whi le manipulations of steroid hormone exposure can influence the display of sexual behaviors, gonadal secretions may not be required for norma l sexual differentiation of the song system in zebra finches. (C) 1997 Academic Press.