Duetting Patterns of Titi Monkeys (Primates, Pitheciidae: Callicebinae) and Relationships with Phylogeny

Long-range vocal communication in socially monogamous titi monkeys is mediated by the production of loud, advertising calls in the form of solos, duets, and choruses. We conducted a power spectral analysis of duets and choruses (simply "duets" hereafter) followed by linear discriminant analysis using three acoustic parameters-dominant frequency of the combined signal, duet sequence duration, and pant call rate-comparing the coordinated vocalizations recorded from 36 family groups at 18 sites in Bolivia, Peru and Ecuador. Our analysis identified four distinct duetting patterns: (1) a donacophilus pattern, <i>sensu largo</i>, characteristic of <i>P. donacophilus</i>, <i>P. pallescens</i>, <i>P. olallae</i>, and <i>P. modestus</i>; (2) a moloch pattern comprising <i>P. discolor</i>, <i>P. toppini</i>, <i>P. aureipalatii</i>, and <i>P. urubambensis</i>; (3) a torquatus pattern exemplified by the duet of <i>Cheracebus lucifer</i>; and (4) the distinctive duet of <i>P. oenanthe</i>, a putative member of the donacophilus group, which is characterized by a mix of broadband and narrowband syllables, many of which are unique to this species. We also document a sex-related difference in the bellow-pant phrase combination among the three taxa sampled from the moloch lineage. Our data reveal a presumptive taxonomic incoherence illustrated by the distinctive loud calls of both <i>P. urubambensis</i> and <i>P. oenanthe</i> within the donacophilus lineage, <i>sensu largo</i>. The results are discussed in light of recent reassessments of the callicebine phylogeny, based on a suite of genetic studies, and the potential contribution of environmental influences, including habitat acoustics and social learning. A better knowledge of callicebine loud calls may also impact the conservation of critically endangered populations, such as the vocally distinctive Peruvian endemic, the San Martin titi, <i>P. oenanthe</i>.