Leptin promotes social context-specific increase in advertisement song effort of male Alston's singing mice.

Animal display behaviors, such as advertisement songs, are flashy and attention grabbing by necessity. In order to balance the costs and benefits of such signals, individuals must be able to assess both their own energetic state and their social environment. In this study, we investigated the role of leptin, a hormonal signal of high energy balance, in regulating the vocal advertisement display of Alston’s singing mouse (Scotinomys teguina). We manipulated perception of energy balance using exogenous leptin, and social environment through acoustic playback, to ask how internal cues of energy availability are integrated with external social cues that promote singing. We found that both song playback and leptin injection promoted increased song effort. In the absence of song playback, leptin altered amplitude modulation in songs, but did not affect song rate. Additionally, we examined hormone and playback effects on non-vocal behaviors and found that leptin may shift physical activity away from cage exploration and toward wheel running. Finally, we found several positive associations between measures related to high song effort. These results demonstrate that male singing mice use both social context and energy balance to govern their investment in advertisement song and that leptin acts as a mediator of this process.

Isolation calls produced by dependent young are a fundamental form of communication. For species in which vocal signals remain important to adult communication, the function and social context of vocal behavior changes dramatically with the onset of sexual maturity. The ontogenetic relationship between these distinct forms of acoustic communication is surprisingly under-studied. We conducted a detailed analysis of vocal development in sister species of Neotropical singing mice, Scotinomys teguina and S. xerampelinus. Adult singing mice are remarkable for their advertisement songs, rapidly articulated trills used in long-distance communication; the vocal behavior of pups was previously undescribed. We recorded 30 S. teguina and 15 S. xerampelinus pups daily, from birth to weaning; 23 S. teguina and 11 S. xerampelinus were recorded until sexual maturity. Like other rodent species with poikilothermic young, singing mice were highly vocal during the first weeks of life and stopped vocalizing before weaning. Production of first advertisement songs coincided with the onset of sexual maturity after a silent period of ≧2 weeks. Species differences in vocal behavior emerged early in ontogeny and notes that comprise adult song were produced from birth. However, the organization and relative abundance of distinct note types was very different between pups and adults. Notably, the structure, note repetition rate, and intra-individual repeatability of pup vocalizations did not become more adult-like with age; the highly stereotyped structure of adult song appeared de novo in the first songs of young adults. We conclude that, while the basic elements of adult song are available from birth, distinct selection pressures during maternal dependency, dispersal, and territorial establishment favor major shifts in the structure and prevalence of acoustic signals. This study provides insight into how an evolutionarily conserved form of acoustic signaling provides the raw material for adult vocalizations that are highly species specific.

Female song elicits increased vocal display effort in both sexes of Alston's singing mouse.

Vocal display behaviours are common throughout the animal kingdom, play important roles in both courtship and aggression, and are frequent subjects of behavioural research. Although females of many species vocalize, an overwhelming fraction of behavioural research has focused on male display. We investigated vocal display behaviours in female singing mice (Scotinomys teguina), small muroid rodents in which both sexes produce songs consisting of trills of rapid, downward frequency sweeps. Previous research established that male singing mice increase song production and engage in precisely timed counter-singing behaviour in response to playback of conspecific male song. We tested whether female singing mice also increased their rate of singing in response to playback of male song, whether they counter-sing, and whether there are sexual dimorphisms in song effort. Our results demonstrate that much like males, female singing mice increase their song effort and counter-sing in response to playback of male song; however, females sing fewer and shorter songs compared to males. This study further informs the understanding of female vocal behaviour and establishes the singing mouse as a valuable model for investigating female vocal display.

Although vocalizations are essential to mammalian sociosexual behaviours, little is known about female preferences for male vocal displays in non-model mammalian species. Here, we characterized female preferences for the advertisement songs of male Alston’s singing mice (Scotinomys teguina). We developed procedures for inducing oestrus, using vaginal perforation as a morphological indicator of oestrus. We then broadcasted ‘high-effort’ and ‘low-effort’ songs recorded from wild-caught males to virgin laboratory-reared females, using a two-choice experiment. Our results indicate that females spent more time investigating speakers playing high-effort songs; surprisingly, this phonotactic response is independent of oestrus status. In wild singing mice, acoustic characteristics of high-effort male songs positively correlate with body condition. Our data suggest that females could use acoustic cues to select mates in good condition, thus providing preliminary support for adaptive mate choice hypotheses. More generally, our results support the hypothesis that elaborate Scotinomys song may be shaped by female choice.

Stress coping styles and singing behavior in the short-tailed singing mouse ( Scotinomys teguina)

Advertisement vocalizations support home-range defense in the singing mouse.

Leptin regulates song effort in Neotropical singing mice (Scotinomys teguina)

Advertisement displays often seem extravagant and expensive, and are thought to depend on the body condition of a signaller. Nevertheless, we know little about how signallers adjust effort based on condition, and few studies find a strong relationship between natural variation in condition and display. To examine the relationship between body condition and signal elaboration more fully, we characterized physiological condition and acoustic displays in a wild rodent with elaborate vocalizations, Alston's singing mouse, Scotinomys teguina We found two major axes of variation in condition-one defined by short-term fluctuations in caloric nutrients, and a second by longer-term variation in adiposity. Among acoustic parameters, song effort was characterized by high rates of display and longer songs. Song effort was highly correlated with measures of adiposity. We found that leptin was a particularly strong predictor of display effort. Leptin is known to influence investment in other costly traits, such as immune function and reproduction. Plasma hormone levels convey somatic state to a variety of tissues, and may govern trait investment across vertebrates. Such measures offer new insights into how animals translate body condition into behavioural and life-history decisions.

Androgens modulate song effort and aggression in Neotropical singing mice

Phoresy is a form of commensalism that has been widely studied, however, limited literature is found about this interaction in Mesoamerican rodents. Rodent trapping in highlands from Western Panama allowed the first report of phoretic pseudoscorpions (Chernetidae), associated with Scotinomys teguina; which also represents the first phoretic record in mammals from Panama.

Sexual Preference in Female Singing Mice (Scotinomys Teguina) Based on Male Song Effort

Sexual displays are some of the most dramatic and varied behaviors that have been documented. The elaboration of such behaviors often relies on the modification of existing morphology. To understand how display elaboration arises, we analyzed the laryngeal anatomy of three species of mice that vary in the presence and complexity of their vocal displays. Mice and rats have a specialized larynx that enables them to produce both low-frequency "audible" sounds, perhaps using vocal fold vibration, as well as distinct mechanisms that are thought to enable higher frequency sounds, such as vocal membrane vibration and intralaryngeal whistles. These mechanisms rely on different structures within the larynx. Using histology, we characterized laryngeal anatomy in Alston's singing mouse (Scotinomys teguina), the northern pygmy mouse (Baiomys taylori), and the laboratory mouse (Mus musculus), which produce different types of vocalizations. We found evidence of a vocal membrane in all species, as well as species differences in vocal fold and ventral pouch size. Presence of a vocal membrane in these three species, which are not known to use vocal membrane vibration, suggests that this structure may be widespread among muroid rodents. An expanded ventral pouch in singing and pygmy mice suggests that these mice may use an intralaryngeal whistle to produce their advertisement songs, and that an expanded ventral pouch may enable lower frequencies than laboratory mouse whistle-produced sounds. Variation in the laryngeal anatomy of rodents fits into a larger pattern across terrestrial vertebrates, where the development and modification of vocal membranes and pouches, or air sacs, are common mechanisms by which vocalizations diversify. Understanding variation in the functional anatomy of relevant organs is the first step in understanding how morphological changes enable novel displays.

Like many adaptive behaviors, acoustic communication often requires rapid modification of motor output in response to sensory cues. However, little is known about the sensorimotor transformations that underlie such complex natural behaviors. In this study, we examine vocal exchanges in Alston's singing mouse (Scotinomys teguina). We find that males modify singing behavior during social interactions on a subsecond time course that resembles both traditional sensorimotor tasks and conversational speech. We identify an orofacial motor cortical region and, via a series of perturbation experiments, demonstrate a hierarchical control of vocal production, with the motor cortex influencing the pacing of singing behavior on a moment-by-moment basis, enabling precise vocal interactions. These results suggest a systems-level framework for understanding the sensorimotor transformations that underlie natural social interactions.

Patterns of repeatability and heritability in the songs of wild Alston's singing mice, Scotinomys teguina