A High-coverage Ancient Genome for Analyzing Arctic Adaptation Mechanisms – the Steller’s Sea Cow Case
General Genetics and Functional Genome Biology
Animal Physiology and Biochemistry
Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
Final Report Abstract
Steller’s sea cow (Hydrodamalis gigas) was first described in 1741 by the German naturalist Georg W. Steller and became extinct after only 27 years. This has been regarded as the first historical extinction of a marine mammal at human hands and represents an iconic example for the catastrophic impact of human overexploitation. In contrast to other extant Sirenians, like dugong and manatee, Steller’s sea cow was giant, with a length of 10 meters and a body weight of up to 10 tons, and cold-water adapted. However, unlike for most of the extinct Pleistocene species, for which complex phenotypes cannot be inferred from fossils, Steller’s detailed phenotypic description and the availability of sufficient fossils provide the unique opportunity to identify the molecular basis of this species’ traits using paleogenomic data. Thus, we sequenced the genomes of 12 H. gigas individuals (2 of them to ~15× coverage), de novo assembled the genome of their closest relative, Dugong dugon, and analyzed the data in light of Steller’s records with the following findings: i) The skin which resembled “the bark of an old oak tree” is a result of lipoxygenase genes’ inactivations. The same mutation in humans and mouse models causes a serious skin condition – ichthyosis – characterized by hyperkeratotic, thickened, scaling skin. This is a unique biological example showing that environmental conditions determine whether a gene loss has disease relevance (human) or an adaptive advantage (Steller’s sea cow). ii) We identified selected genes along Steller’s sea cow lineage that regulate energy homeostasis and weight gain. This correlates well to their reportedly thick blubber, which facilitated seasonal fasting and life in a cold habitat. iii) The H. gigas lineage experienced long-term decline during much of the Pleistocene, suggesting that environmental changes also played a key role in their extinction. Steller’s sea cow brings awareness to ocean biodiversity conservation, especially since their closest living relative, the dugong, is now endangered. The dugong genome we provide can support ongoing conservation research and contribute to the underrepresented marine mammal genomes. Our findings highlight how ancient genomes can reveal unique aspects of species’ phenotypes and demographic histories, especially when complemented by thorough phenotypic records.
Publications
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Genomic basis for skin phenotype and cold adaptation in the extinct Steller’s sea cow. Science Advances, 8(5).
Le Duc, Diana; Velluva, Akhil; Cassatt-Johnstone, Molly; Olsen, Remi-Andre; Baleka, Sina; Lin, Chen-Ching; Lemke, Johannes R.; Southon, John R.; Burdin, Alexander; Wang, Ming-Shan; Grunewald, Sonja; Rosendahl, Wilfried; Joger, Ulrich; Rutschmann, Sereina; Hildebrandt, Thomas B.; Fritsch, Guido; Estes, James A.; Kelso, Janet; Dalén, Love ... & Schöneberg, Torsten
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Is it inappropriate to ask for your age? Evaluating parameter impact on tree dating in a challenging clade (Macroscelidea). Molecular Phylogenetics and Evolution, 183, 107756.
Hagemann, Justus; Hofreiter, Michael; Bibi, Faysal; Holroyd, Patricia & Arnold, Patrick
