No abstract

Vocal and gestural sequences of several primates have been found to conform to two general principles of information compression: the compensation between the duration of a construct and that of its components (Menzerath-Altmann law) and an inverse relationship between signal duration and its occurrence (Zipf's law of abbreviation). Even though Zipf's law of brevity has been proposed as a universal in animal communication, evidence on non-human primate vocal behavior conformity to linguistic laws is still debated, and information on strepsirrhine primates is lacking. We analyzed the vocal behavior of the unique singing lemur species (Indri indri) to assess whether the song of the species shows evidence for compression. As roars have a chaotic structure that impedes the recognition of each individual utterance, and long notes are usually given by males, we focused on the core part of the song (i.e., the descending phrases, composed of two-six units).Our results indicate that indris' songs conform to Zipf's and Menzerath-Altmann linguistic laws. Indeed, shorter phrases are more likely to be included in the song, and units' duration decrease at the increase of the size of the phrases. We also found that, despite a sexual dimorphism in the duration of both units and phrases, these laws characterize sequences of both males and females. Overall, we provide the first evidence for a trade-off between signal duration and occurrence in the vocal behavior of a strepsirrhine species, suggesting that selective pressures for vocal compression are more ancestral than previously assumed within primates.

In mammals, olfactory communication plays an essential role in territorial and mating dynamics. Scent depositions in various species, including lemurs, can be placed via marking or overmarking (marking over previous depositions). We focused on the role that marking and overmarking play in territorial defence and intrasexual competition. We investigated these aspects in diademed sifaka (Propithecus diadema) in the primary rainforest of Maromizaha (eastern Madagascar). We collected scent marking data for five groups from April to November 2018 and from May to December 2019. We aimed to understand whether the lemurs deposited scent marks homogeneously across the home range and whether sex, rank, and occurrence of intergroup encounters affected the lemur’s deposition rate. We also asked whether males overmarked adult females more often than other depositions, and the marking and overmarking rates changed between the migration and non-migration seasons. We found that scent marking was performed higher in peripheral and overlapping areas than in the home range central areas. In addition, males had higher scent marking rates, but intergroup encounters did not affect deposition rates. Males showed higher rates of overmarking and primarily targeted dominant females’ depositions, particularly during the “migration” season (including premating and mating seasons). Our findings suggest a border-marking strategy in Propithecus diadema. More frequent scent marking in the “migration” season suggests intrasexual competition in males. Our results suggest that marking is associated with territorial and resource defence, suggesting that it plays a role in monopolizing females using a mate-guarding strategy and may also serve for males’ self-advertisement to females and subordinate depositors.

21The diversity of qualitative approaches and analytical methods has often undermined 22 comparative research on primate vocal repertoires. The purpose of the present work is 23 to introduce a quantitative method based on dynamic time warping to the study of 24 repertoire size in Eulemur spp. We obtained a large sample of calls of E. coronatus, 25 E. flavifrons, E. fulvus, E. macaco, E. mongoz, E. rubriventer and E. rufus, recorded 26between 1999 and 2013 from captive and wild lemurs. We inspected recordings 27 visually using spectrograms, then cut and saved high-quality vocal emissions to single 28 files for further analysis. We extracted the acoustic features of all vocalizations of a 29 species using the Hidden Markov Model toolkit, an application of dynamic time 30warping, then compared cepstral coefficients (a feature widely used in automatic 31 speaker recognition) pairwise. We analysed the results using Affinity Propagation 32 clustering. We found that Eulemur species share most of their vocal repertoire but 33 species-specific calls determine repertoire size differences. Repertoire size varied 34 from 9 and 14 vocalisation types among species, with a mean of 11. Group size is 35 thought to favour the evolution of vocal complexity at the species level but our results 36 suggest that this relationship should be reconsidered, as Eulemur rubriventer has the 37 largest vocal repertoire but shows a relatively small average group size when 38 compared to congeneric species.