3.3.2 Alouatta guariba (Humboldt, 1812)

Type: No original type available. Hill (1962) notes for Mycetes bicolor (Gray, 1845) (in the British Museum, adult male, skin and skull, 1844. 5.14.16) that the label indicates it was collected by Parzudaki on the Orinoco. Napier (1976, p. 76) noted that “it appears to be more closely related to A. belzebul,” and she catalogued it under Alouatta sp. (p. 88).

Type locality: Brazil. Restricted by Cabrera (1957) to Rio Paraguassú, Bahia (Hill 1962; Napier 1976).

Common name: Brown howler.

This species inhabits the Atlantic Forest of Brazil, south of the Rio São Francisco (Rylands et al. 1996) (Fig. 3.1). The taxonomy of this taxon is quite complex and there is some confusion about its correct name. Rylands and Brandon-Jones (1998) argued that É. Geoffroy Saint-Hilaire (1806) mentioned the name “guariba ” in reference to A. belzebul not as a binomial but as a common name. “Guariba ” is the name for howlers in the Brazilian Amazon and É. Geoffroy Saint-Hilaire used it to distinguish A. belzebul from the spider monkey Ateles belzebuth. The name guariba, used for the brown howler by Humboldt (1812), is not as such a junior homonym as argued by Hershkovitz (1963) and is available for this taxon. (Humboldt [1812] predated the Stentor fuscus of É. Geoffroy Saint-Hilaire [1812] by 2 months [Thomas 1913]). Gregorin (2006) disagrees with this, however, and supports the view of Hershkovitz (1963) that guariba is an objective junior homonym and that the correct name to use for this taxon is A. fusca (Geoffroy Saint-Hilaire, 1812). Here we follow the interpretation of Rylands and Brandon-Jones (1998) in using the name A. guariba for this species.

Two different forms have been identified based on pelage coloration: a northern brown howler A. g. guariba and a southern form in which males are darker than females, the southern brown howler A. g. clamitans Cabrera, 1940. This distinction is supported by cytogenetic (de Oliveira 1995; 1996; de Oliveira et al. 2002) and molecular (Harris et al. 2005; de Mello Martins et al. 2011) data. Based on morphological analyses of cranial and hyoid bone features, Gregorin (2006) considers that these two forms should be considered full species. Analyses of mitochondrial DNA variation among the populations of A. guariba in three localities (in the states of Rio de Janeiro, São Paulo, and Santa Catarina) show the existence of two mitochondrial lineages (de Mello Martins et al. 2011). These monophyletic lineages are apparently consistent with the northern and southern forms, which are in contact in the state of São Paulo. Unfortunately, de Mello Martins et al. (2011) do not provide information on the genetic distance between these lineages, but according to their Fig. 2, it is similar to that observed among different haplotypes of A. belzebul. Although this study supports some distinction between A. g. guariba and A. g. clamitans, the taxonomic recognition as full species will require further genetic analyses that include a larger number of samples across the range of this species, representatives of other recognized howler species, as well as the use of multiple loci.