Ultrasonic vocalizations in immature gerbils: emission rate and structural changes after neonatal exposure to androgen.

Emission rates of stereotyped ultrasonic vocalizations in sexually immature Mongolian gerbils are sexually dimorphic. Calling rates in interacting pairs of females are characteristically higher than in male dyads. Juvenile vocalizations produced during paired encounters show a similar spectrographic structure to adult courtship calls. Three experiments examined the developmental effects of a single injection of 100 micrograms testosterone propionate given to 0-12 h old female gerbils on total emission rates, spectrographic structure of ultrasonic vocalizations and display of other social-sexual play behaviors during encounters between immature androgenized females and stimulus partners. Reduced total rates of juvenile ultrasound emission were recorded in TP-treated females paired with stimulus males or females when compared with control male-male or female-female pairs in Experiment 1 and confirmed in Experiment 2. Male-typical play mounting was increased in pairs containing androgenized females in Experiment 2. In Experiment 3, emission rates of female-type Warble sounds were significantly decreased and the rate of male-type Steep curvilinear and Long rectilinear calls significantly increased in androgenized female and stimulus animal dyads compared with control animal pairs. New spectrographic forms of ultrasound, with readily discernible single or multiple upper harmonics, were recorded in androgenized female-stimulus partner interactions. We conclude that androgenization of female neonates (a) masculinized and also defeminized sexually dimorphic ultrasound emission rates, and virilized nonvocal behavior, suggesting a direct effect on organization of the central nervous system; (b) influenced the sonagraphic structure of calls. It is proposed that organization of juvenile vocal rates in gerbils primarily involves a number of androgen sensitive mechanisms in the central and peripheral nervous systems. However, androgenization also appeared to have an indirect role on calling rates by affecting treated female-stimulus partner relationships.

Ontogeny of sexually dimorphic ultrasonic vocalizations in Mongolian gerbils.

Sexual differentiation of emission rates (Experiment 1) and physical structure of ultrasonic vocalizations (Experiment 2) were investigated in Mongolian gerbils between 17 and 85 days of age. Animals from different litters were allowed to interact in iso- and heterosexual pairs. Vocalization rates increased in all groups, reaching a plateau at approximately day 56. Female pups had significantly higher rates of all vocalizations than male pairs before the plateau stage. Five stereotypic categories of physical structure were easily distinguished and confirmed by sound spectrographic analysis. Only mid-range frequencies of vocalizations appeared to decline throughout the juveniles' lives: this change may communicate the animal's age. Two male and one female categories were sexually dimorphic and similar in structure to those made during courtship interactions. Rates of male-type vocalizations appear to increase as testicular androgens start rising.