A new study by scientists from the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW), has revealed significant cryptic diversity within two-toed sloths (Choloepus) in Amazonia, challenging the long-established taxonomy of the genus. This international effort involved key South American collaborators. Utilizing the first genome-wide dataset from multiple two-toed sloth populations, the study published in the journal “Molecular Phylogenetics and Evolution” provides critical new evidence that past environmental changes shaped the sloths’ evolutionary history, and highlights an urgent need for taxonomic revision and updated conservation assessment and strategies.

The Amazon basin is one of the most important biodiversity hotspots on the planet. Until know, scientists assumed that there are two species of two-toed sloths in that region, the Hoffmann’s two-toed sloth (Choloepus hoffmanni) and the Linnaeus’s two-toed sloth (Choloepus didactylus). A genomic analysis conducted by an international team of scientists lead by Leibniz-IZW demonstrated that the Hoffmann’s two-toed sloth is paraphyletic, meaning some populations currently classified as C. hoffmanni (found east of the Andes) are actually more closely related to Linnaeus’s two-toed sloth. The findings support the existence of previously unknown Choloepus lineages, suggesting the genus may consist of at least three species. The study determined that the divergence of these lineages aligns with the onset of Pleistocene climatic changes and the final phase of Andean uplift, which created geographic barriers that isolated populations.

Beyond taxonomy, the research provided crucial demographic insights for conservation. The study suggests that Amazonian sloth populations, particularly the one found in East Amazonian lineage, are currently under stress. This population exhibits lower genetic diversity and higher levels of inbreeding, patterns that the authors suggest are linked to the region’s climatic instability and recent deforestation, particularly in the highly threatened deforestation arc. These genomic insights confirm that these distinct evolutionary lineages will require independent conservation assessments to safeguard their unique genetic diversity amidst the increasing threat of habitat loss and fragmentation.

“Amazonian sloths are both relics of an ancient evolutionary past and sentinels of today’s deforestation. The discovery of cryptic lineages and potentially new species underscores the urgency to accelerate sloth research, a mission our group is actively pursuing”, says Dr. Camila J. Mazzoni, senior author of the paper and leader of the Leibniz-IZW Sloth Genomics project line.

This highly collaborative study, involving scientists from the Leibniz-IZW Department of Evolutionary Genetics, the Berlin Center for Genomics in Biodiversity Research, the Federal University of Minas Gerais (UFMG), the Instituto Nacional de Pesquisas da Amazônia (INPA), the Federal University of Rondonia, Institut Pasteur de la Guyane and conservation NGOs dedicated to Xenarthra, such as Instituto Tamanduá, provides a vital foundation for the future of sloth conservation. It demonstrates the importance of genomic research in uncovering hidden biodiversity in the Amazon and directly informs conservation planning, ensuring that efforts are directed toward protecting unique evolutionary units before they face irreversible impacts from human activities.