Female indris determine the rhythmic structure of the song and sustain a higher cost when the chorus size increases

Abstract

Among the behavioral traits shared by some nonhuman primate species and humans there is singing. Unfortunately, our understanding of animals' rhythmic abilities is still in its infancy. Indris are the only lemurs who sing and live in monogamous pairs, usually forming a group with their offspring. All adult members of a group usually participate in choruses that are emitted regularly and play a role in advertising territorial occupancy and intergroup spacing. Males and females emit phrases that have similar frequency ranges but may differ in their temporal structure. We examined whether the individuals' contribution to the song may change according to chorus size, the total duration of the song or the duration of the individual contribution using the inter-onset intervals within a phrase and between phrases. We found that the rhythmic structure of indri's songs depends on factors that are different for males and females. We showed that females have significantly higher variation in the rhythm of their contribution to the song and that, changes according to chorus size. Our findings indicate that female indris sustain a higher cost of singing than males when the number of singers increases. These results suggest that cross-species investigations will be crucial to understanding the evolutionary frame in which such sexually dimorphic traits occurred.

Rhythm in speech and animal vocalizations: a cross‐species perspective

“…Research on individual vocal rhythms in nonhuman primates is scarce: most work has investigated either group vocal rhythms or individual nonvocal rhythms . Focusing on individual vocal rhythms, early descriptive work remarked temporal regularities in gelada monkeys’ vocalizations, a claim which is intriguing but purely descriptive, unfortunately not supported by quantitative data or statistical inference.…”

“…Unlike common mice, Alston's singing mice do perform vocal duets: in this neotropical rodent, call timing is controlled by different neural circuitry depending on whether singing is performed in isolation or socially. [26][27][28] Research on individual vocal rhythms in nonhuman primates is scarce: most work has investigated either group vocal rhythms 29,30 or individual nonvocal rhythms. [31][32][33] Focusing on individual vocal rhythms, early descriptive work remarked temporal regularities in gelada monkeys' vocalizations, 34 a claim which is intriguing but purely descriptive, unfortunately not supported by quantitative data or statistical inference.…”

Interactive rhythms across species: the evolutionary biology of animal chorusing and turn‐taking

“…But what does chorusing have to offer to turntaking researchers? The empirical study of animal choruses has been ongoing for almost a century across species and modalities, 7,8,[33][34][35][36][37][38][39] and their study partly overlaps with animal turn-taking, a more recent and growing ( Fig. 1) topic of comparative research.…”

“…This historical focus on individual language capacities, partly due to a generativist tradition in language sciences, is rapidly changing . Unanswered questions regarding how individual communicative rhythms are shaped by group interactions and modulated by social behavior are starting to be addressed . The study of conversation and turn‐taking is taking center stage …”

“…5,6 Unanswered questions regarding how individual communicative rhythms are shaped by group interactions and modulated by social behavior are starting to be addressed. [7][8][9][10] The study of conversation and turn-taking is taking center stage. [11][12][13] To understand the origins and evolution of language, the comparative approach targets analogous or homologous language-relevant traits in nonhuman animals.…”