Sex Differences In Vocalizations Research Articles

Sex differences in frequencies in a species with modest sexual size dimorphism

ABSTRACT Sex differences in vocalizations are found across the animal kingdom, which may be due to different vocal apparatus, call function, and context. Rock hyraxes (Procavia capensis) of both sexes are vocal, but the sexes differ in repertoire size, call usage, and amplitude. In this study we examined sex differences in vocalization frequencies and predicted that they will be low and that frequency ranges will overlap since sexual size dimorphism in this species is modest (~ 15%). We utilized two datasets: recordings of captive hyraxes using a condenser microphone; and audio files of wild-living individuals recorded via a miniature recorder mounted on a collar. With the exclusion of two proximate call types recorded in the wild, all calls featured an ultrasonic component. However, in females there was an effect of duration on minimal frequency. Warning trills, which are heard by humans far away, featured the highest maximal visible harmonic in both datasets. No relationship was found between calling distance and the maximal harmonic in males, while in wild females, distant calls featured higher frequencies. Our results show sex differences in hyrax vocalization frequencies. Exploring the information encoded in frequencies beyond the human hearing range may expand our understanding of animal communication.

Species and sex differences in vocalizations between sex-role reversed shorebirds, Northern Jacana (Jacana spinosa) and Wattled Jacana (J. jacana)

Species-specific vocalizations can act as a reproductive isolating mechanism between closely related populations. We analyzed vocal differences between 2 hybridizing species of sex-role reversed polyandrous shorebirds, the Northern Jacana (Jacana spinosa) and Wattled Jacana (J. jacana). We found that Northern Jacana calls have higher fundamental frequency and peak frequency than Wattled Jacana calls. We also compared calls between females and males, as both jacana species are sex-role reversed and females compete for male mates. Males produce calls with a higher fundamental and peak frequency and shorter notes than females. These results suggest that vocal differences between Northern and Wattled jacanas have the potential to act as a behavioral mediator of interspecific interactions, and that sex differences in vocalizations may relate to sex-role reversal in territorial defense and mate attraction.

Sex differences in vocalizations to familiar or unfamiliar females in mice.

Mice, both wild and laboratory strains, emit ultrasound to communicate. The sex differences between male to female (male–female) and female to female (female–female) ultrasonic vocalizations (USVs) have been discussed for decades. In the present study, we compared the number of USVs emitted to familiar and unfamiliar females by both males (male–female USVs) and females (female–female USVs). We found that females vocalized more to unfamiliar than to familiar females. By contrast, males exhibited more USVs to familiar partners. This sexually dimorphic behaviour suggests that mice change their vocal behaviour in response to the social context, and their perception of the context is based on social cognition and memory. In addition, because males vocalized more to familiar females, USVs appear to be not only a response to novel objects or individuals, but also a social response.

Production and perception of sex differences in vocalizations of Wied's black-tufted-ear marmosets (Callithrix kuhlii).

Males and females from many species produce distinct acoustic variations of functionally identical call types. Social behavior may be primed by sex-specific variation in acoustic features of calls. We present a series of acoustic analyses and playback experiments as methods for investigating this subject. Acoustic parameters of phee calls produced by Wied's black-tufted-ear marmosets (Callithrix kuhlii) were analyzed for sex differences. Discriminant function analyses showed that calls contained sufficient acoustic variation to predict the sex of the caller. Several frequency variables differed significantly between the sexes. Natural and synthesized calls were presented to male-female pairs. Calls elicited differential behavioral responses based on the sex of the caller. Marmosets became significantly more vigilant following the playback of male phee calls (both natural and synthetic) than following female phee calls. In a second playback experiment, synthesized calls were modified by independently manipulating three parameters that were known to differ between the sexes (low-, peak-, and end-frequency). When end-frequency-modified calls were presented, responsiveness was differentiable by sex of caller but did not differ from responses to natural calls. This suggests that marmosets did not use end-frequency to determine the sex of the caller. Manipulation of peak-and low-frequency parameters eliminated the discrete behavioral responses to male and female calls. Together, these parameters may be important features that encode for the sex-specific signal. Recognition of sex by acoustic cues seems to be a multivariate process that depends on the congruency of acoustic features.

Androgen Receptors and Sexual Dimorphisms in the Larynx of the Bullfrog

As in most anuran amphibians, both male and female bullfrogs (Rana catesbeiana) vocalize. Sex differences in vocalizations in the bullfrog may be due to sex differences in the larynx. We examined the laryngeal muscle to determine whether it possessed androgen receptors and whether there were morphological sexual dimorphisms in the larynx. Using a polyclonal antibody and immunocytochemistry, we found androgen receptors in the laryngeal dilator muscle of both sexes. Males possessed approximately 13% more receptor-positive muscle nuclei than females. We also stained the dilator muscle for the presence of succinate dehydrogenase. Density of staining for the enzyme was significantly greater in male muscle than in female muscle, indicating greater oxidative capacity of muscle in males. This procedure also showed both a significantly greater cross-sectional area for the dilator muscle in males and a greater area for individual fibers. Male muscle consisted almost entirely of fast-twitch oxidative/glycolytic fibers. Female muscle contained a mixture of fast-twitch glycolytic fibers and two subclasses of fast-twitch oxidative/glycolytic fibers. Finally, both the length and width of the entire laryngeal complex and the length and width of the dilator were significantly greater in males than in females. In summary, laryngeal muscle of bullfrogs possessed androgen receptors and is thus likely to be androgen sensitive. Androgens, during development or at adulthood, may be responsible for the anatomic and enzymatic sexual dimorphisms in the larynx.

Sex Differences in the Vocalizations and Syrinx of the Collared Dove (Streptopelia decaocto)

We examined differences between sexes in the structure of vocalizations and the syrinx of the Collared Dove (Streptopelia decaocto). Seven vocal characteristics were mea- sured to determine the degree of sex differences in the structure of the perch-coo. Sex differences in vocalizations occurred in vocal activity levels and spectrotemporal parameters. Females produced fewer and shorter coo bouts. Coos produced by females also had a higher fundamental frequency, more overtones, a different temporal pattern, and tended to be less stereotyped. Discriminant function analysis revealed that sound percentage, followed by modulation percentage and fundamental frequency, were best at discriminating between the sexes. Based on the magnitude of sex differences and acoustic discrimination ratios, the latter two characters are the ones most likely to be used for vocal sex recognition. In general, the syrinx of female Collared Doves is a reduced copy of the one found in males. Trachea size and the number of tracheal and bronchial rings had high loadings on the principal com- ponents that showed significant differences between the sexes. In addition to general size differences, the number of ventromedially thickened rings and length of the tracheosyringeal membrane also were strongly correlated with these principal components. Length and height of the primary bronchi did not appear to differ between the sexes but were bilaterally asymmetrical only in males. The combination of vocal and anatomical data provides evidence that morphological aspects contribute to sexual dimorphism in vocalizations. Received 26 February 1996, accepted 26 July 1996.