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| Steller’s Sea Cow | Hydrodamalis gigas Zimmermann, 1780 Sirenian distribution according to the IUCN Red List (2020) in Le Duc, Velluva, Cassatt-Johnstone, ... et Schöneberg, 2022. drawing by R. Ellis (1741) |
Abstract
Steller’s sea cow, an extinct sirenian and one of the largest Quaternary mammals, was described by Georg Steller in 1741 and eradicated by humans within 27 years. Here, we complement Steller’s descriptions with paleogenomic data from 12 individuals. We identified convergent evolution between Steller’s sea cow and cetaceans but not extant sirenians, suggesting a role of several genes in adaptation to cold aquatic (or marine) environments. Among these are inactivations of lipoxygenase genes, which in humans and mouse models cause ichthyosis, a skin disease characterized by a thick, hyperkeratotic epidermis that recapitulates Steller’s sea cows’ reportedly bark-like skin. We also found that Steller’s sea cows’ abundance was continuously declining for tens of thousands of years before their description, implying that environmental changes also contributed to their extinction.
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| Molecular basis for Steller’s sea cow’s skin phenotype. (A) Sirenian distribution according to the International Union for Conservation of Nature Red List (2020). All sequenced Steller’s sea cow individuals originate from the Commander Islands. (B) Translated multiple sequence alignment of the ALOXE3 and ALOX12B genes showing amino acid sequence conservation corresponding to the human proteins (bold in Steller’s sea cow) and the position of the premature stop codons. (C) Arachidonate lipoxygenases structure, which is composed of the PLAT (Polycystin-1, Lipoxygenase, and Alpha-Toxin) domain and the enzymatic LIPOXYGENASE core domain. Premature stop codons in Steller’s sea cow ALOXE3 and ALOX12B genes are depicted in red. Truncating variants described in human patients and located downstream from the Steller’s sea cow premature stop codons are depicted in black. (D) Left: Steller’s sea cow drawing according to Steller’s description from 1741 (image by R. Ellis). Right: Image of a patient with ichthyosis; detail depicts scaling and hyperkeratosis. |
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| Sirenian distribution according to the International Union for Conservation of Nature Red List (2020) |
Hydrodamalis gigas Zimmermann, 1780
Diana Le Duc, Akhil Velluva, Molly Cassatt-Johnstone, ... et Torsten Schöneberg. 2022. Genomic Basis for Skin Phenotype and Cold Adaptation in the Extinct Steller’s Sea Cow. SCIENCE ADVANCES. 8, 5. DOI: 10.1126/sciadv.abl6496
