Arginine vasotocin affects vocal behavior but not selective responses to conspecific calls in male túngara frogs.

Arginine vasotocin (AVT) and its homolog arginine vasopressin (AVP) modulate social behavior, including social communication. In anuran amphibians, male-male competition and female mate choice rely heavily on acoustic signaling. Behavioral experiments show that AVT influences motivation to call and vocal production. It may also influence how males process and respond to socially relevant auditory stimuli, but few studies have explored this possibility in this taxon. Túngara frogs produce a "whine" that is used for species recognition; in competition with other males they append one or more attractive "chucks" to the whine. Frequency modulation in the whine is an important cue for recognizing conspecifics, and gating of conspecific signals begins in the auditory midbrain. We used dynamic playback experiments to investigate the effects of exogenous AVT on males' responses to stimuli with species-typical and altered frequency modulation. We used avoidance of call overlap as evidence that a male recognizes a stimulus as salient and the production of attractive chucks as evidence of his competitive response to a proximate rival. We used call rate, whine duration, and whine frequency as measures of motivation and motor production. Males responded selectively to a stimulus with species-typical frequency modulation. Following treatment with AVT, they increased call rate and altered whines and chucks in a way that suggests increased air flow during the whine. We did not, however, find evidence that treatment with AVT alters the salience of frequency modulation in recognizing and responding to acoustic signals, at least for the stimuli used in this study.

A bond graph approach to modeling the anuran vocal production system.

Air-driven vocal production systems such as those found in mammals, birds, and anurans (frogs and toads) combine pneumatic and mechanical elements in species-specific ways to produce a diversity of communication signals. This study uses bond graphs to model a generalized anuran vocal production system. Bond graphs allow an incremental approach to modeling dynamic physical systems involving different domains. Anurans provide an example of how signal diversity results from variation in the structure and behavior of vocal system elements. This paper first proposes a bond graph model of the integrated anuran vocal system as a framework for future study. It then presents a simulated submodel of the anuran sound source that produces sustained oscillations in vocal fold displacement and air flow through the larynx. The modeling approach illustrated here should prove of general applicability to other biological sound production systems, and will allow researchers to study the biomechanics of vocal production as well as the functional congruence and evolution of groups of traits within integrated vocal systems.

Treatment with arginine vasotocin alters mating calls and decreases call attractiveness in male túngara frogs.

The peptide hormone arginine vasotocin (AVT) and its mammalian homolog arginine vasopressin modulate a variety of social behaviors in vertebrates. In anurans, AVT influences the production of advertisement calls, the acoustic signals that males use to attract females and repel rival males. In this study, we investigate the effects of AVT on call characteristics in the túngara frog (Physalaemus pustulosus). Túngara frogs produce a "whine" that is important for species recognition; they may also produce a second, attractive call component, the "chuck". We used a field playback experiment to determine changes in male calling behavior following treatment with AVT. A previous study showed that AVT alters call rate and the production of chucks; in the current analysis, we focus on changes in the whine. Males produce shorter whines with higher initial frequencies following treatment with AVT. Call changes do not vary with a social stimulus. We also used female phonotaxis experiments to investigate the effects of call changes on female mate choice. Females disfavor the calls produced by males treated with exogenous AVT. We suggest that AVT influences motivation to call and the motor control of call production, but that over-stimulation of the vocal system limited the production of attractive calls in this experimental context.

Arginine vasotocin promotes calling behavior and call changes in male túngara frogs.

In the túngara frog, Physalaemus pustulosus, males alter calling behavior with changes in their social environment, adding 'chucks' to their advertisement calls in response to the calls of conspecific males. Other studies demonstrate that adding chucks increases the attractiveness of calls to females but also increases the risk of bat predation. In the current study, subcutaneous injections of the neuropeptide hormone arginine vasotocin (AVT) significantly increased chuck production in male túngara frogs. The effects of AVT on chuck production did not depend on the presence of playback stimuli, suggesting that AVT increased either the males' general motivation to produce chucks or their responsiveness to the calls of distant males. Injections of AVT also increased the probability that males would call and decreased the latency to call after injection, supporting the hypothesis that AVT influences motivation to call. Finally, AVT inhibited a drop in call rate after the termination of a playback stimulus and increased call rate at a lower dose of AVT. The effects of AVT on chucks and call rate appear to be independent of each other, as there was no correlation between change in chuck production and change in call rate in individual males. We conclude that AVT may play an important role in socially-mediated call changes that result from competition for mates. The behavioral changes induced by AVT might increase a male's attractiveness to females, and also may be consistent with an aggressive response to another túngara frog male.