Early estrogen treatment alone causes female zebra finches to produce learned, male‐like vocalizations

Abstract

The male zebra finch produces learned song and long calls while the female does not. This difference in behavior is believed to result from the action of sex steroids on brain areas responsible for vocal production and learning. In this study, the female zebra finch was used to explore further the specific role sex steroids play in vocal masculinization. We show that estradiol (E2) treatment at birth was sufficient to masculinize the vocal behavior of female zebra finches. Thirteen of 18 females treated with E2 as nestlings produced song-like vocalizations. Fifteen of 18 produced long calls with male-typical features. The degree of masculinization varied between individuals. Of the 15 early E2 females that produced at least one type of male-like vocalization, 7 showed evidence of vocal learning from their tutors. The ability of E2 to cause masculinization of vocal behavior was age dependent: treatment from birth was most effective, treatment at 20 days of age was partially effective, and treatment in adulthood was ineffective. The effect of subsequent testosterone exposure in adulthood differed depending on the quality of the vocalization produced after E2 treatment alone. These results suggest that E2 may play a more important role than previously thought in the development of sex differences in vocal behavior. Furthermore, this study demonstrates that exogenous E2 treatment alone can induce vocal learning.

Zebra finch sexual differentiation: The aromatization hypothesis revisited

“…There is no doubt that without early masculinization, via estradiol (E2; see below), they will not sing in adulthood. However, while most studies found that singing in females requires not only early hormone administration, but also treatment with androgens in adulthood (Gurney, 1982;Gurney and Konishi, 1980;Pohl-Apel and Sossinka, 1984), at least one study does suggest that early E2 alone is sufficient (Simpson and Vicario, 1991a).…”

“…In most cases, the production of song seems to require treatment with T in adulthood, but at least one study (Simpson and Vicario, 1991a) suggests that the early E2 treatment alone is sufficient. The quality and quantity of the adult song are variable both within and across studies (Adkins-Regan and Ascenzi, 1987;Adkins-Regan et al, 1994;Gurney and Konishi, 1980), although in general it appears that the longer the birds are treated in the first few weeks after hatching, the more male-like the song becomes (Pohl-Apel and Sossinka, 1984;Simpson and Vicario, 1991a). In addition to masculinizing singing behavior, E2 treatment during the first 2 weeks after hatching can shift the sexual partner preference of zebra finch females, such that in adulthood they prefer to be near females rather than males in two-choice tests (interestingly, unisex housing produces the same effect) .…”

Muscle-dependent and hormone-dependent differentiation of the vocal control premotor nucleus robustus archistriatalis and the motornucleus hypoglossus pars tracheosyringealis of the zebra finch

“…The volume and neuron size of the RA of males increase dramatically after postnatal day (P)30, whereas the female RA undergoes developmental arrest or degeneration (Konishi and Akutagawa, 1985). The direct action of testosterone and estrogens on the forebrain is thought to shift the fate of the vocal control areas toward a male phenotype (Gurney and Konishi, 1980;Gurney, 1981Gurney, , 1982Konishi and Akutagawa, 1985;Herrmann and Arnold, 1991;Simpson and Vicario, 1991;Grisham et al, 1993;Gahr and Metzdorf, 1999). The development of sex differences of the syringeal musculature and of the nXIIts at P20 (Lohmann, 1997) precedes the period of hormone-triggered masculinization of forebrain vocal areas of female zebra finches (Konsihi and Akutagawa, 1985;Gahr and Metzdorf, 1999).…”

Circulating estrogens in a male songbird originate in the brain.

“…Correspondingly, the telencephalic neural system controlling song is much larger in males than females (1). However, ifyoung females are treated with E, they develop a masculinized neural song system and the capacity to sing as adults (2)(3)(4)(5)(6). These E effects on the song system are extensive; they influence neuron survival, size, dendritic arbor, or hormone sensitivity within several brain structures (7)(8)(9)(10)(11).…”