Two Amazonian howler monkeys now have distinct species names: Alouatta iroi, in the north-west of the basin, and Alouatta matogrossensis, in the south of the Brazilian Amazon. Their description, published in the scientific journal “Communications Biology”, does not mean that these animals have only just appeared. It recognises that populations already present had been grouped under a classification that did not reflect their differences.
The work combines genomic data, physical characteristics and specimens held in natural history collections. It calls for a rethink of the map of Amazonian biodiversity, but also for three often-confused stages to be distinguished: identifying a species, describing where it lives and establishing the measures needed for its conservation.
A classification refined using several lines of evidence
Howler monkeys belong to the genus Alouatta, found in Central and South America. The study analyses genome-wide data to examine relationships between species and populations. Its abstract states that the analysis covers 11 species. The authors say they combined these data with morphological evidence — that is, observable physical characteristics — studied in specimens.
This combination matters because a single difference is not always enough to define a species. Populations may differ in appearance without being durably separated in evolutionary terms; conversely, differentiated lineages may be difficult to recognise by sight. Genomic data make it possible to compare their relationships, while physical characteristics and the provenance of specimens help link these differences to actual populations.
The names adopted are Alouatta iroi, the Pantepui red howler, and Alouatta matogrossensis, the Mato Grosso red howler. Mongabay’s report places the former in the north-west of Amazonia and the latter in the south of the Brazilian Amazon. Museums play an active scientific role here: their collections preserve individuals and provenance information that can be compared using more recent genetic tools. An old specimen cannot, on its own, tell the story of a population, but it makes it possible to compare descriptions and samples over time.
Rivers, forests and population history
The study abstract places most of the diversification of the genus in Amazonia during the last million years. It links this history to several factors: geographical barriers, including the Amazonian rivers and the Andes, as well as ecological gradients, such as savannah and forest mosaics. A barrier can reduce exchanges between groups without automatically creating a new species: separation, its duration and population history all contribute to a more complex evolutionary process.
The case of the Branco River illustrates this question. According to Mongabay, the researchers found distinct genetic lineages on either side of the watercourse. The distribution of populations, their genome and their physical characteristics together contribute to the recognition of Alouatta iroi. Geography thus helps explain differences that have developed over time.
A map that groups several populations under a single name can therefore conceal different distributions and evolutionary trajectories. Distinguishing them makes it possible to examine more precisely the pressures to which each is exposed.
Naming a species does not give it protected status
For Alouatta matogrossensis, the conservation issue is particularly tangible. Its range overlaps the arc of deforestation, a vast area of forest transformation where agricultural expansion contributes to habitat loss and fragmentation. Fragmentation breaks up continuous forest into separate patches. For arboreal animals, this discontinuity can make it harder to move between wooded areas and isolate groups.
The researchers believe the species could fall into a very high threat category, but a formal assessment has yet to be carried out. This distinction matters: a new scientific description is not the same as an official listing on the IUCN Red List, nor does it mean that a protection measure has already been implemented. Rather, the classification work provides a basis for separately examining the area occupied, the pressures and the risk of extinction.
In the north, the Bem Querer hydroelectric dam project on the Branco is a potential pressure mentioned by Mongabay for Alouatta iroi and its close relative Alouatta macconnelli. A more precise picture of the species’ distribution makes it possible to identify more clearly which populations could be affected by the project.
Canopy bridges installed by the Reconecta project in Mato Grosso are intended to reconnect forest fragments. Mongabay reports that Alouatta matogrossensis have been observed using these structures. These crossings show that the structures are being used. Long-term monitoring is still needed to determine their effects on movement and populations.
A third population to reassess
The work also reopens the discussion about the howler monkeys of Trinidad and Tobago, previously classified as Alouatta seniculus insulanus. The researchers recommend recognising them as a distinct species, Alouatta insulanus. This is a proposed recognition reported alongside the study: it should not be confused with the two Amazonian species formally described in the same work.
The distinction is a reminder that taxonomy, the science of classifying and naming organisms, evolves with the data and interpretations. A more precise classification helps us ask better questions: which populations are separate, where do they live and what pressures are they each facing? Protection, in turn, depends on appropriate assessments and action. Naming a species makes an issue more visible; it is not enough to preserve the forest on which it depends.
References
- Mongabay, “Genetic study describes two new species of Amazonian howler monkeys”
- “Communications Biology”, study abstract
- University of Salford, introduction to the two species
A red howler monkey, Alouatta seniculus, photographed in Venezuela in 2015. This related species illustrates the genus Alouatta; it is not a photograph of the two newly described species.
Fernando Flores — Venezuelan red howler | Araguato (Alouatta seniculus) — Wikimedia Commons — CC BY-SA 2.0.
