How many pygmy marmoset (Cebuella Gray, 1870) species are there? A taxonomic re-appraisal based on new molecular evidence

The pygmy marmoset, Cebuella pygmaea , the smallest of the New World monkeys, has one of the largest geographical distributions of the Amazonian primates. Two forms have been recognized: Cebuella pygmaea pygmaea (Spix, 1823), and C. p. niveiventris Lonnberg, 1940. In this study, we investigated if the separation of pygmy marmosets into these two clades can be corroborated by molecular data. We also examine and compare coloration of the pelage in light of the new molecular results. We analyzed the mtDNA cytochrome b gene and, for the first time for any Neotropical primate, we used a reduced representation genome sequencing approach (ddRADseq) to obtain data for recently collected, geographically representative samples from the Rio Japura, a northern tributary of the Rio Solimoes and from the Javari, Jutai, Jurua, Madeira and Purus river basins, all tributaries south of the Solimoes. We estimated phylogenies and diversification times under both maximum likelihood and Bayesian inference criteria. Our analysis showed two highly supported clades, with intraclade divergences much smaller than interclade divergences, indicating two species of Cebuella : one from the Rio Japura and one to the south of Solimoes. The interpretation of our results in light of the current taxonomy is not trivial however. Lonnberg stated that the type of Spix’s pygmy marmoset (type locality ‘near Tabatinga’) was obtained from the south of the Solimoes, and his description of the distinct niveiventris from Lago Ipixuna, south of the Solimoes and several kilometres east of Tabatinga, was based on a comparison with specimens that he determined as typical pygmaea that were from the upper Rio Jurua (south of the Solimoes). As such it remains uncertain whether the name pygmaea should be applicable to the pygmy marmosets north of the Rio Solimoes (Tabatinga type locality) or south (near Tabatinga but across the Solimoes). Finally, our analysis of pelage coloration revealed three phenotypic forms: 1) south of the Rio Solimoes, 2) Eirunepe-Acre, upper Jurua basin; and 3) Japura. More samples from both sides of Solimoes in the region of Tabatinga will be necessary to ascertain the exact type locality for Spix’s pygmaea and to resolve the current uncertainties surrounding pygmy marmoset taxonomy.