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| Couple of Homotherium chasing a horse. in Barnett, Westbury, Sandoval-Velasco, ... et Gilbert, 2020. |
Highlights:
• Nuclear genome and exome analyses of extinct scimitar-toothed cat, Homotherium latidens
• Homotherium was a highly divergent lineage from all living cat species (∼22.5 Ma)
• Genetic adaptations to cursorial and diurnal hunting behaviors
• Relatively high levels of genetic diversity in this individual
Summary
Homotherium was a genus of large-bodied scimitar-toothed cats, morphologically distinct from any extant felid species, that went extinct at the end of the Pleistocene. They possessed large, saber-form serrated canine teeth, powerful forelimbs, a sloping back, and an enlarged optic bulb, all of which were key characteristics for predation on Pleistocene megafauna. Previous mitochondrial DNA phylogenies suggested that it was a highly divergent sister lineage to all extant cat species. However, mitochondrial phylogenies can be misled by hybridization, incomplete lineage sorting (ILS), or sex-biased dispersal patterns, which might be especially relevant for Homotherium since widespread mito-nuclear discrepancies have been uncovered in modern cats. To examine the evolutionary history of Homotherium, we generated a ∼7x nuclear genome and a ∼38x exome from H. latidens using shotgun and target-capture sequencing approaches. Phylogenetic analyses reveal Homotherium as highly divergent (∼22.5 Ma) from living cat species, with no detectable signs of gene flow. Comparative genomic analyses found signatures of positive selection in several genes, including those involved in vision, cognitive function, and energy consumption, putatively consistent with diurnal activity, well-developed social behavior, and cursorial hunting. Finally, we uncover relatively high levels of genetic diversity, suggesting that Homotherium may have been more abundant than the limited fossil record suggests. Our findings complement and extend previous inferences from both the fossil record and initial molecular studies, enhancing our understanding of the evolution and ecology of this remarkable lineage.
Keywords: Homotherium, paleogenome, genomics, comparative genomes, adaptation, phylogeny, ancient DNA, palaeogenome, diversity, selection
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| Figure 2: Depiction of 18 of the 31 Genes under Positive Selection with High Values (Free Ratio > 2) in the Homotherium Genome Hypothetical functions and the adaptive insights that these provide on the species’ behavior, morphology, and functional adaptations are also shown. Additional genes not depicted here are likely involved in cellular processes such as apoptosis, protein synthesis, and protein signaling, as well as immunity/cancer, olfaction, and reproduction. ... |
Ross Barnett, Michael V. Westbury, Marcela Sandoval-Velasco, Filipe Garrett Vieira, Sungwon Jeon, Grant Zazula, Michael D. Martin, Simon Y.W. Ho, Niklas Mather, Shyam Gopalakrishnan, Jazmín Ramos-Madrigal, Marc de Manuel, M. Lisandra Zepeda-Mendoza, Agostinho Antunes, Aldo Carmona Baez, Binia De Cahsan, Greger Larson, Stephen J. O’Brien, Eduardo Eizirik, Warren E. Johnson, Klaus-Peter Koepfli, Andreas Wilting, Jörns Fickel, Love Dalén, Eline D. Lorenzen, Tomas Marques-Bonet, Anders J. Hansen, Guojie Zhang, Jong Bhak, Nobuyuki Yamaguchi and M. Thomas P. Gilbert. 2020. Genomic Adaptations and Evolutionary History of the Extinct Scimitar-Toothed Cat, Homotherium latidens. Current Biology. DOI: 10.1016/j.cub.2020.09.051
