Genetic Survey Finds Two New Howler Monkey Species Hidden in the Amazon

Geneticists have identified two previously unrecognized species of howler monkey in the Amazon basin, the first new species described in that genus in 85 years, after a genome-wide comparison of monkey populations across South and Central America turned up genetic divergences too deep to be explained by existing taxonomy.

The two new species, Alouatta iroi and Alouatta matogrossensis, were described in a paper published in Communications Biology, a Nature-family journal, by a team led by researchers at the University of Salford in England working with collaborators in Brazil and elsewhere. The paper, titled "Genome-wide analyses reveal recent diversification and hidden diversity in Amazonian howler monkeys, including two new species," combined genomic sequencing with morphological comparisons of museum specimens to re-examine the boundaries between howler monkey populations that had previously been lumped together or only loosely distinguished.

Alouatta matogrossensis, given the common name Mato Grosso red howler monkey, was identified in southern Amazonia. Alouatta iroi was documented in the Guiana Shield region of northern Amazonia. The discovery brings the number of recognized species in the genus Alouatta from 13 to 15. The last time a new howler monkey species was named was in 1941, when the Swedish zoologist Einar Lönnberg described Alouatta puruensis.

What the genomes showed

The research team sequenced and compared genome-wide data from 11 of the Amazon basin's 13 previously recognized howler monkey species, pairing that genetic evidence with physical measurements from preserved museum specimens, an approach researchers describe as integrative taxonomy. According to the paper, most of the genetic diversity within Amazonian howler monkeys arose recently in evolutionary terms, within roughly the last one million years, a comparatively short span for a primate radiation that researchers say likely originated west of the Andes mountains before expanding across the Amazon basin.

The study attributes much of that recent diversification to geography. Major Amazonian rivers, including the Amazon itself along with the Rio Branco and the Xingu, appear to have acted as long-standing barriers that separated howler monkey populations from one another for long enough that they diverged genetically, even where their outward appearance remained similar. Transitional habitats between savanna and forest, described in the paper as ecotones, are identified as another driver of the split. The result is a picture of a primate genus that looks more uniform from a distance than its underlying genetics suggest, with cryptic diversity that only becomes visible once researchers look past physical appearance and sequence the DNA directly.

A fast-closing window for conservation

Howler monkeys are large-bodied, loud-calling primates found from Mexico to Argentina, and more than two-thirds of the genus's existing taxa are already classified as threatened, according to the study. The paper's authors argue that the newly described species illustrate a broader problem for conservation planning in the tropics: species can remain scientifically undocumented, and therefore unprotected under formal assessment frameworks, even as the forests that sustain them are cleared or fragmented.

That concern is sharpest for Alouatta matogrossensis. Its range lies in southern Amazonia, a region researchers and conservation groups have identified as among the fastest-deforesting parts of the Amazon basin, driven by cattle ranching and soy cultivation. Because the species has only now been formally named, it has not yet been evaluated for the International Union for Conservation of Nature's Red List, the standard reference used by governments and conservation organizations to prioritize protection. Habitat loss, forest fragmentation and road mortality are among the threats the paper's authors cite as already affecting howler monkey populations generally across the basin, including, potentially, species that have not yet been given a name at all.

Road deaths are a particular focus of related conservation work. The Reconecta Project, led by the Brazilian road ecologist Fernanda Abra and run in partnership with the Smithsonian's National Zoo, builds canopy bridges over highways that cut through Amazonian forest, including a stretch of the BR-174 highway, to give tree-dwelling primates including howler monkeys a way to cross without descending to the road surface. The project is cited in the new paper's authors' public remarks as the kind of conservation measure that becomes more urgent once a population is confirmed to be a distinct, and therefore individually vulnerable, species.

Researchers' reaction

Jean Boubli, a professor at the University of Salford's Environmental Research and Innovation Centre and senior author on the paper, said in a statement released by the university that the timing of the discovery was significant given the pressures facing the region. Romina Batista, the paper's corresponding author and an honorary postdoctoral research associate at Salford, framed the finding in terms of what it means for protection efforts going forward.

"Understanding the different species in existence is the first step towards protecting them," said Romina Batista, the study's corresponding author.

In its announcement of the findings, the University of Salford said Boubli described the discovery as coming "at a critical time," pointing to deforestation, climate change and habitat loss as converging threats to Amazonian primates, and said the research team hopes the new species descriptions will help conservation organizations prioritize which populations need protection most urgently.

What happens next

The paper's authors say their genome-wide approach sampled 11 of the genus's 13 previously recognized species, meaning related populations elsewhere in the howler monkeys' range, from Central America through the southern reaches of South America, have not yet been subjected to the same level of genetic scrutiny. The authors suggest further undescribed diversity may exist within those unsampled populations and within other Amazonian taxa more broadly, a pattern that has emerged repeatedly in recent genomic surveys of Amazonian wildlife.

Formal conservation status assessments for both newly named species have not yet been completed, a process typically carried out through the IUCN's Red List framework once a species has been formally described in the scientific literature. Researchers say that process, along with continued monitoring of howler monkey populations in rapidly developing parts of the southern Amazon, is the immediate next step, alongside further genomic sampling of the howler monkey populations the current study did not cover.