Extensive genome-wide analysis of the Amazonian two-toed sloth (genus Choloepus) reveals that these remarkable creatures possess greater genetic diversity than previously understood, suggesting the potential existence of undiscovered species.
The two-toed sloth is a slow-moving, tree-dwelling mammal that inhabits the lush rainforests of Central and South America.
Interestingly, although named for their two clawed digits on the front legs, these animals do not literally have “two digits.” This characteristic differentiates them from their three-toed counterparts.
Belonging to the genus Choloepus, the three-toed sloth is classified within the monophyletic family Choloepodidae.
Currently, scientists acknowledge two main species: Hoffmann’s two-toed sloth (Choloepus hoffmanni), found from Central America to parts of South America, and Linnaeus’s two-toed sloth (Choloepus didactylus), predominantly located in the Amazon Basin.
Dr. Camila Mazzoni of the Leibniz Institute for Zoo and Wildlife Research highlights that Choloepus didactylus is monotypic with a wide distribution throughout the Amazon, while Choloepus hoffmanni comprises five recognized subspecies in Central America, as well as northwestern parts of Venezuela, Colombia, and Ecuador.
Both species are believed to coexist in the western Amazon, a region known for its rich concentration of terrestrial mammals, exhibiting distinct morphological traits such as fur coloration and skeletal characteristics.
However, significant overlaps in body size and coat color present challenges for accurate taxonomic classification.
To investigate the phylogenetic and biogeographical history of this genus in the Amazon, the researchers compiled existing mitochondrial data and generated new genomic datasets, including mitochondrial and whole-genome sequences from Choloepus individuals sampled across three remote Amazonian regions.
This comprehensive analysis allowed them to assess population structure, lineage relationships, demographic history, and genomic diversity patterns among sampled lineages.
The findings revealed that Choloepus hoffmanni is not a singular, cohesive lineage as previously thought.
Instead, populations east of the Andes share closer genetic relationships with Choloepus didactylus than with their western counterparts, indicating a “paraphyletic” classification that fails to capture the species’ true evolutionary history.
Even more remarkably, the research uncovered at least three deeply divergent genetic lineages among Amazonian sloths, suggesting that many others may yet be identified.
This hidden diversity dates back millions of years. By comparing nuclear and mitochondrial DNA, they reconstructed the sloth evolutionary timeline, revealing significant divergences linked to historical environmental changes.
The separation of sloths on opposite sides of the Andes likely occurred around 4.6 million years ago during the final uplift of the mountains that reshaped South America’s landscape.
Then, approximately 2.6 million years ago, the Quaternary Ice Age began, fragmenting the Amazon rainforest into isolated habitats, which would have introduced barriers to migration for these arboreal creatures, setting them on separate evolutionary paths.
Genetic analyses also indicated that sloth populations have experienced expansions and contractions in response to glacial cycles throughout history.
Dr. Mazzoni emphasized, “The Amazon sloth represents both an ancient evolutionary relic and a critical indicator of current deforestation trends.” She asserted, “The discovery of cryptic lineages and potentially new species underscores the urgency of advancing sloth research, which our team actively pursues.”
“This collaborative research lays a crucial foundation for sloth conservation efforts.”
“Our findings demonstrate the pivotal role of genomic research in revealing the hidden biodiversity of the Amazon, directly informing conservation strategies to protect unique evolutionary units before they are threatened by human activities.”
For further details, refer to the published study in Molecular Phylogenetics and Evolution.
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Larissa S. Arantes et al. 2026. Genomic insights into the evolutionary history and puzzling diversity of the three-toed sloth (Choloepus) in the Amazon. Molecular Phylogenetics and Evolution 221: 108620; doi: 10.1016/j.ympev.2026.108620
Source: www.sci.news
