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Ultrasonic vocalizations in golden hamsters (Mesocricetus auratus) reveal modest sex differences and nonlinear signals of sexual motivation.

Fernández-Vargas M, Johnston RE - PLoS ONE (2015)

Bottom Line: We found modest sexual differences between repertoires.Interestingly, however, this high variability, augmented by the prevalence of chaos and frequency jumps, could be the result of increased vocal effort.Thus, the sex differences found could be the result of different sex preferences but also of a sex difference in calling motivation or condition.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Cornell University, Ithaca, NY, United States of America.

ABSTRACT
Vocal signaling is one of many behaviors that animals perform during social interactions. Vocalizations produced by both sexes before mating can communicate sex, identity and condition of the caller. Adult golden hamsters produce ultrasonic vocalizations (USV) after intersexual contact. To determine whether these vocalizations are sexually dimorphic, we analyzed the vocal repertoire for sex differences in: 1) calling rates, 2) composition (structural complexity, call types and nonlinear phenomena) and 3) acoustic structure. In addition, we examined it for individual variation in the calls. The vocal repertoire was mainly composed of 1-note simple calls and at least half of them presented some degree of deterministic chaos. The prevalence of this nonlinear phenomenon was confirmed by low values of harmonic-to-noise ratio for most calls. We found modest sexual differences between repertoires. Males were more likely than females to produce tonal and less chaotic calls, as well as call types with frequency jumps. Multivariate analysis of the acoustic features of 1-note simple calls revealed significant sex differences in the second axis represented mostly by entropy and bandwidth parameters. Male calls showed lower entropy and inter-quartile bandwidth than female calls. Because the variation of acoustic structure within individuals was higher than among individuals, USV could not be reliably assigned to the correct individual. Interestingly, however, this high variability, augmented by the prevalence of chaos and frequency jumps, could be the result of increased vocal effort. Hamsters motivated to produce high calling rates also produced longer calls of broader bandwidth. Thus, the sex differences found could be the result of different sex preferences but also of a sex difference in calling motivation or condition. We suggest that variable and complex USV may have been selected to increase responsiveness of a potential mate by communicating sexual arousal and preventing habituation to the caller.

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Relationships among acoustic parameters obtained from the analysis of the entire full spectrum of simple 1-note calls produced by both males and estrous females.Spearman correlations between mean calling rates (number of USV/min) and mean duration (ms) (A) and frequency bandwidth (kHz) (B). Spearman correlations between mean duration (ms) and mean frequency bandwidth (kHz) (C) and mean energy (u) (D).
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pone.0116789.g004: Relationships among acoustic parameters obtained from the analysis of the entire full spectrum of simple 1-note calls produced by both males and estrous females.Spearman correlations between mean calling rates (number of USV/min) and mean duration (ms) (A) and frequency bandwidth (kHz) (B). Spearman correlations between mean duration (ms) and mean frequency bandwidth (kHz) (C) and mean energy (u) (D).

Mentions: We analyzed a total of 1103 1-note simple USV from 14 male and 12 female subjects recorded during the post-interaction period following an opposite sex interaction. The PCA retained the first principal components explaining 83.6% of the total variance. However, we did not find significant sex differences between any of the principal components (S1 Table). However, we found that male calls were significantly shorter than female calls (Kruskal-Wallis test: X2 = 4.89, P = 0.027) and had higher minimum frequency (Kruskal-Wallis test: X2 = 6.61, P = 0.0101) (Table 2). As explained in the methods, the acoustic analysis of the full spectrum of the calls included the principal carrier and all its harmonically related and unrelated components (e.g. harmonic frequencies, resonances). However, hamster calls were loud, atonal and characterized by frequent chaos, which often made frequency contours obscure and hard to detect. Thus, it was not surprising to find little information from the parameter extraction. The high variability observed may indicate that these parameters are dynamic and rapidly modulated by the internal state of the caller. In fact, we found that the total number of calls produced by subjects and call duration were predictors of some acoustic parameters. The number of calls per minute was positively correlated with call duration (Spearman ρ = 0.59, P = 0.001) and delta frequency (Spearman ρ = 0.41, P = 0.0376) (Fig. 4A,B). When tested separately for each sex, calling rate predicted call duration (males: Spearman ρ = 0.29, P = 0.3; females Spearman ρ = 0.64, P = 0.02) and delta frequency (males: Spearman ρ = -0.04, P = 0.8; females Spearman ρ = 0.57, P = 0.05) just in females and not in males. Thus, females that called more produced longer vocalizations and of greater bandwidth. Additionally, longer calls showed higher delta frequency (Spearman ρ = 0.38, P = 0.05) and higher energy (Spearman ρ = 0.39, P = 0.05) (Fig. 4C,D) in hamsters regardless of sex.


Ultrasonic vocalizations in golden hamsters (Mesocricetus auratus) reveal modest sex differences and nonlinear signals of sexual motivation.

Fernández-Vargas M, Johnston RE - PLoS ONE (2015)

Relationships among acoustic parameters obtained from the analysis of the entire full spectrum of simple 1-note calls produced by both males and estrous females.Spearman correlations between mean calling rates (number of USV/min) and mean duration (ms) (A) and frequency bandwidth (kHz) (B). Spearman correlations between mean duration (ms) and mean frequency bandwidth (kHz) (C) and mean energy (u) (D).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4340904&req=5

pone.0116789.g004: Relationships among acoustic parameters obtained from the analysis of the entire full spectrum of simple 1-note calls produced by both males and estrous females.Spearman correlations between mean calling rates (number of USV/min) and mean duration (ms) (A) and frequency bandwidth (kHz) (B). Spearman correlations between mean duration (ms) and mean frequency bandwidth (kHz) (C) and mean energy (u) (D).
Mentions: We analyzed a total of 1103 1-note simple USV from 14 male and 12 female subjects recorded during the post-interaction period following an opposite sex interaction. The PCA retained the first principal components explaining 83.6% of the total variance. However, we did not find significant sex differences between any of the principal components (S1 Table). However, we found that male calls were significantly shorter than female calls (Kruskal-Wallis test: X2 = 4.89, P = 0.027) and had higher minimum frequency (Kruskal-Wallis test: X2 = 6.61, P = 0.0101) (Table 2). As explained in the methods, the acoustic analysis of the full spectrum of the calls included the principal carrier and all its harmonically related and unrelated components (e.g. harmonic frequencies, resonances). However, hamster calls were loud, atonal and characterized by frequent chaos, which often made frequency contours obscure and hard to detect. Thus, it was not surprising to find little information from the parameter extraction. The high variability observed may indicate that these parameters are dynamic and rapidly modulated by the internal state of the caller. In fact, we found that the total number of calls produced by subjects and call duration were predictors of some acoustic parameters. The number of calls per minute was positively correlated with call duration (Spearman ρ = 0.59, P = 0.001) and delta frequency (Spearman ρ = 0.41, P = 0.0376) (Fig. 4A,B). When tested separately for each sex, calling rate predicted call duration (males: Spearman ρ = 0.29, P = 0.3; females Spearman ρ = 0.64, P = 0.02) and delta frequency (males: Spearman ρ = -0.04, P = 0.8; females Spearman ρ = 0.57, P = 0.05) just in females and not in males. Thus, females that called more produced longer vocalizations and of greater bandwidth. Additionally, longer calls showed higher delta frequency (Spearman ρ = 0.38, P = 0.05) and higher energy (Spearman ρ = 0.39, P = 0.05) (Fig. 4C,D) in hamsters regardless of sex.

Bottom Line: We found modest sexual differences between repertoires.Interestingly, however, this high variability, augmented by the prevalence of chaos and frequency jumps, could be the result of increased vocal effort.Thus, the sex differences found could be the result of different sex preferences but also of a sex difference in calling motivation or condition.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Cornell University, Ithaca, NY, United States of America.

ABSTRACT
Vocal signaling is one of many behaviors that animals perform during social interactions. Vocalizations produced by both sexes before mating can communicate sex, identity and condition of the caller. Adult golden hamsters produce ultrasonic vocalizations (USV) after intersexual contact. To determine whether these vocalizations are sexually dimorphic, we analyzed the vocal repertoire for sex differences in: 1) calling rates, 2) composition (structural complexity, call types and nonlinear phenomena) and 3) acoustic structure. In addition, we examined it for individual variation in the calls. The vocal repertoire was mainly composed of 1-note simple calls and at least half of them presented some degree of deterministic chaos. The prevalence of this nonlinear phenomenon was confirmed by low values of harmonic-to-noise ratio for most calls. We found modest sexual differences between repertoires. Males were more likely than females to produce tonal and less chaotic calls, as well as call types with frequency jumps. Multivariate analysis of the acoustic features of 1-note simple calls revealed significant sex differences in the second axis represented mostly by entropy and bandwidth parameters. Male calls showed lower entropy and inter-quartile bandwidth than female calls. Because the variation of acoustic structure within individuals was higher than among individuals, USV could not be reliably assigned to the correct individual. Interestingly, however, this high variability, augmented by the prevalence of chaos and frequency jumps, could be the result of increased vocal effort. Hamsters motivated to produce high calling rates also produced longer calls of broader bandwidth. Thus, the sex differences found could be the result of different sex preferences but also of a sex difference in calling motivation or condition. We suggest that variable and complex USV may have been selected to increase responsiveness of a potential mate by communicating sexual arousal and preventing habituation to the caller.

Show MeSH
Related in: MedlinePlus