Uncertainty Regarding Species Delimitation, Geographic Distribution, and the Evolutionary History of South-Central Amazonian Titi Monkey Species (Plecturocebus, Pitheciidae)

Abstract

Platyrrhine primate taxonomy is a rapidly evolving area of research. The recent description of the Parecis titi monkey, Plecturocebus parecis, has raised substantial questions regarding the taxonomy, distribution, and evolutionary history of titi taxa from south-central Amazonia. There is only a single documented record of P. parecis, which is the type locality, with uncertainty regarding species monophyly. Moreover, there are questions surrounding the distribution and pelage patterns of the poorly studied P. cinerascens and P. parecis, which further highlight the uncertainty regarding the taxonomic validity of this new species. Here, we investigate the taxonomy, distribution, and evolutionary history of these lineages through new field work and assessment of pelage pigmentation patterns from 25 localities, as well as maximum likelihood and Bayesian phylogenetic reconstructions based on two mitochondrial and 11 nuclear loci for 19 and 10 specimens of Plecturocebus, respectively. Our mitochondrial results recover a paraphyletic arrangement for the four P. parecis type specimens that show three distinct haplotypes, with the holotype showing a close affinity to P. bernhardi. Our morphological analysis reveals a north–south clinal bleaching gradient through the Aripuanã-Sucundurí/Juruena interfluve from an all-grayish morphotype associated with P. cinerascens, through intermediary morphotypes with increasingly whitish hairs on the beard, hands, feet, and tail, to the most whitish morphotype described as P. parecis. Based on these findings, we present hypotheses to explain the taxonomy, distribution, and evolutionary history of P. cinerascens and P. parecis and discuss the significance of introgression among titi taxa from southern Amazonia given the lack of study systems for natural hybridization in platyrrhine primates. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.