Abstract
The increasing interest in the evolution of human language has led several fields of research to focus on primate vocal communication. The ‘singing primates’, which produce elaborated and complex sequences of vocalizations, are of particular interest for this topic. Indris (Indri indri) are the only singing lemurs and emit songs whose most distinctive portions are “descending phrases” consisting of 2-5 units. We examined how the structure of the indris’ phrases varied with genetic relatedness among individuals. We tested whether the acoustic structure could provide conspecifics with information about individual identity and group membership. When analyzing phrase dissimilarity and genetic distance of both sexes, we found significant results for males but not for females. We found that similarity of male song-phrases correlates with kin in both time and frequency parameters, while, for females, this information is encoded only in the frequency of a single type. Song phrases have consistent individual-specific features, but we did not find any potential for advertising group membership. We emphasize the fact that genetic and social factors may play a role in the acoustic plasticity of female indris. Altogether, these findings open a new perspective for future research on the possibility of vocal production learning in these primates.
Highlights
Vocal signals often play a critical role in animal communication[1]
Four principal components accounted for 83.2% of the total variance of the temporal variables of the descending phrases of two units (DP2, see Supplementary Table S1), and five components accounted for 92.5% of the variance of frequency parameters
The results presented here come from the first intra-population analysis of indris comparing the acoustic characteristics of song phrases and genetic relatedness
Summary
Vocal signals often play a critical role in animal communication[1]. While many species make a conspicuous use of vocalizations, a limited number of taxa communicate using a sequence of vocal emissions, usually termed songs[2]. Early findings on song development in the zebra finches (Taeniogypta guttata) suggested that, while male birds develop their song during a sensitive period for vocal production learning[6], song culture appears as a multi-generational phenotype, partially encoded in the genes of an isolated founding population In this species, juvenile birds, that imitate isolated tutors, changed particular characteristics of the songs. Because vocal learning has been typically associated with singing, studying the effects of genetics and social factors on the vocal output of primates that communicate using songs (i.e., tarsiers, gibbons, indris, titi monkeys15) is of great interest. Concordance between song and genetic diversity across the crested gibbons[19] suggests that genes may play a major role in shaping song structure Both hybrid males and females showed intermediate song structure compared to the songs of the parental species (Hylobates lar x H. muelleri[20]; Hylobates lar x H. pileatus[21]). We aimed to understand whether the acoustic structure of phrases differed when analyzed within closely (e.g.; father-offspring, mother-offspring) and distantly related indris in the population of Maromizaha
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