Behavior of Male and Female Zebra Finches Treated With an Estrogen Synthesis Inhibitor as Nestlings

Abstract

In order to test hypotheses about the organizational role of early estrogen in the sexual differentiation of behavior in zebra finches (Taeniopygia guttata), newly hatched birds were given one of three treatments: (1) daily injection with an aromatase inhibitor (fadrozole hydrochloride) for the first week; (2) the same treatment for the first two weeks; (3) daily injection of the vehicle for one or two weeks. As adults, birds were implanted with testosterone propionate and underwent a three-phase testing procedure designed to measure singing, dancing, copulation, and preferences for male vs female partners. Males were completely unaffected by fadrozole hydrochloride treatment; they sang, danced, and mounted at control levels, and like control males they preferred female partners. Females were similarly unaffected, with one important exception: those treated with fadrozole hydrochloride during the first week preferred to be spend time near females instead of males in choice tests, unlike control females. These results suggest that a model of zebra finch sexual differentiation in which estrogen organizes male-typical behavior is unlikely to be correct. At the same time, they provide evidence that a key dimorphic feature of mate choice, preference for opposite-sex birds (sexual orientation), may result from organizational hormone actions during the early post-hatching period in this pair-bonding species.

Removal of adult males from the rearing environment increases preference for same-sex partners in the zebra finch

“…In laboratory colonies of zebra finches, it is not uncommon to see an occasional same-sex pair among nonexperimental birds, especially among females with limited access to males (Adkins-Regan et al 1996), which would explain the low, but nonzero, interest in same-sex birds seen in the control groups here. The significantly elevated incidence of this behaviour in the male-removal groups is none the less striking.…”

“…Thus they could hear but not see or contact birds of the opposite sex. Unisex housing at this age does not by itself alter sexual partner preference in either sex (Adkins-Regan et al 1996).…”

Aromatase inhibition blocks the activation and sexual differentiation of appetitive male sexual behavior in Japanese quail.

“…Partner preference is also known to be sexually differentiated in other avian species and in mammals, and a number of studies have demonstrated that perinatal hormones, including estrogens, have organizing effects on sex-typical partner preferences in adulthood (Adkins-Regan, Mansukhani, Seiwert, & Thompson, 1994; Adkins-Regan, Yang, & Mansukhani, 1996; Bakker, Van Ophemert, & Slob, 1993; Baum, Erskine, Kornberg, & Weaver, 1990; Brand, Kroonen, Mos, & Slob, 1991; Brand & Slob, 1991). The present experiment clearly indicates that embryonic estrogens have important effects on the organization of this behavioral response in quail, and this species may therefore constitute an excellent model to study the neural mechanisms underlying this important aspect of sexual behavior.…”

Mate Selection, Sexual Orientation, and Pair Bonding

“…Little experimental work on this topic has been made in animal models, but in one species of songbirds, the zebra finch (T. guttata), which is known to form long-term sociosexual bonds, research in the Adkins-Regan laboratory has clearly demonstrated that young females treated with estrogens during the first 2 weeks post-hatch will prefer other females over males in two-choice proximity tests, and will pair with females in mixed-sex aviaries where they have ample choice of partners [192][193][194] (see Refs 193,195 for discussion of a few puzzling aspects of this research, including the fact that unexpectedly treatment with an aromatase inhibitor produces a similar change in partner preference). Little experimental work on this topic has been made in animal models, but in one species of songbirds, the zebra finch (T. guttata), which is known to form long-term sociosexual bonds, research in the Adkins-Regan laboratory has clearly demonstrated that young females treated with estrogens during the first 2 weeks post-hatch will prefer other females over males in two-choice proximity tests, and will pair with females in mixed-sex aviaries where they have ample choice of partners [192][193][194] (see Refs 193,195 for discussion of a few puzzling aspects of this research, including the fact that unexpectedly treatment with an aromatase inhibitor produces a similar change in partner preference).…”