Encoding of Arousal and Physical Characteristics in Audible and Ultrasonic Vocalizations of Mongolian Gerbil Pups Testing Common Rules for Mammals

Abstract

In mammals, common rules for the encoding of arousal and physical characteristics of the sender are suggested based on a similar vocal production apparatus. In this study, we want to investigate to what extent vocalizations of developing Mongolian gerbil pups fulfill these rules. We recorded vocalizations of 28 Mongolian gerbil pups in four developmental stages using a separation paradigm, suggested to induce different arousal levels. For low arousal, a pup was placed in an arena isolated from its siblings and parents; for high arousal, the pup was additionally stressed through the simulation of a predator. An unsupervised cluster analysis revealed three call types: ultrasonic (USV), audible vocalizations (ADV), and transitions between both (USV-ADV). The USV and USV-ADV rate showed an age-dependent decrease, contrasting an age-dependent increase for ADVs. Vocal correlates for the encoding of arousal were found for USVs and of physical characteristics for USVs and ADVs. However, the pattern of encoding these cues differed between call types and only partly confirmed the common rules suggested for mammals. Our results show that divergent encoding patterns do not only differ between species but also between call types within a species, indicating that coding rules can be shaped by socio-ecological factors or call type specific production mechanisms.

Keywords: age; arousal; audible vocalizations; body weight; development; individual signatures; mammal; sex; ultrasonic vocalizations; vocal ontogeny.

Figure 1

t-SNE plot visualizing results of unsupervised cluster analysis. Colors represent separate clusters matching the preliminary visual classification of the call types; USV—ultrasonic vocalization, ADV—audible vocalization, USV-ADV—transition from USV to ADV part.

Figure 2

Percentage of pups producing ADVs, USVs and USV-ADVs in the Low and High arousal condition across Age groups; d. = postnatal days.

Figure 3

Boxplots for (A) Call duration and (B) Mean fundamental frequency of USVs during High and Low arousal condition. Boxplots represent lower and upper quartile, thick black line is the median, whiskers are the non-outlier range, yellow dots represent vocalizations plotted as a beeswarm, ** p < 0.01.

Figure 4

Scatterplots for (A) USV Call duration, (B) ADV Call duration, (C) USV Maximum fundamental frequency, and (D) ADV Maximum fundamental frequency across body weight. Dots = vocalizations, thick line = regression line.

Figure 5

Boxplots for (A) USV Call duration, (B) ADV Call duration, (C) USV Maximum fundamental frequency and (D) ADV Maximum fundamental frequency across different Age groups. Boxplots represent lower and upper quartile, thick black line is the median, whiskers are the non-outlier range, yellow dots represent vocalizations plotted as a beeswarm, d. = postnatal days; ** p < 0.01.

Figure 6

Boxplots for (A) USV Bandwidth and (B) ADV Bandwidth, (C) USV Mean fundamental frequency and (D) ADV Mean fundamental frequency for females and males. Boxplots represent lower and upper quartile, thick black line is the median, whiskers are non-outlier range, yellow dots represent vocalizations plotted as a beeswarm, * p < 0.05, n.s. = non-significant differences.

Figure 7

Comparison of vocalizations recorded in the Low versus High arousal conditions before and after eye opening for Mongolian gerbils with findings in the literature for mouse lemurs [26] and kittens [25].