A multinational team of researchers has successfully sequenced and analyzed the genome of the Steller’s sea cow (Hydrodamalis gigas). Their results show that this large aquatic mammal definitively embarked on the road toward extinction long before the arrival of the first Paleolithic hunter-gatherers in the Beringia, which is estimated to have occurred at least 25,000-30,000 years ago.
The Steller’s sea cow is an extinct species of marine mammal from the order Sirenia, which contains four living species: three species of manatees and the dugong, the closest species to the Steller’s sea cow as has been shown in previous studies.
It inhabited the coastal areas of the North Pacific Ocean — including the Bering Sea — during the Pleistocene and Holocene epoch.
The last population of the Steller’s sea cow was discovered in 1741 by the Vitus Bering’s Great Northern Expedition along the coasts of the Commander Islands, and it was gone by the end of the 18th century.
The Steller’s sea cow was up to 11 tons in mass and up to 10 m in length; however, adult animals from the last population were significantly smaller.
German biologist Georg Wilhelm Steller, who participated in the Vitus Bering’s Expedition, stated that the animal weighted around 4.5-5.9 tons and had a body length of 7.5 m. He also documented it as a stenobiontic species that adapted to brown algae diets (mainly kelp) and the cold coastal conditions of the Bering Sea region.
Recent studies suggested that the climate changes and Paleolithic human hunting may have reduced Steller’s sea cow population levels before European sailors made the last strike in the evolutionary history of the species.
They also suggested that the marine animal was doomed to extinction, even without the direct killing of the last population, because of the overhunting on sea otters and the co-occurring loss of kelp forests in this region.
To investigate the population history of the Steller’s sea cow, Dr. Artem Nedoluzhko of Nord University in Norway and colleagues sequenced the extinct mammal’s nuclear and mitochondrial genomes.
To do this, they extracted DNA from a well-preserved petrous bone housed in the Kaliningrad Museum of the Ocean.
“We showed that well-preserved Steller’s sea cow petrous bone was a good source of endogenous DNA,” they noted.
The scientists found that the nuclear and mitogenomes of the Steller’s sea cow contain around 1.24 billion base pairs and 16,896 base pairs, respectively.
Their analysis shows that the gene diversity of the last population of the Steller’s sea cow was low and comparable to the last woolly mammoth population that inhabited Wrangel Island 4,000 years ago.
“This marine mammal was most likely a victim of significant climate changes during the Pleistocene and the associated environmental and biodiversity changes,” the authors said.
“The sea level and temperature changes during the Late Pleistocene may have negatively affected the Steller’s sea cow populations because they inhabited the coastal zone.”
“Due to several morphological traits Steller’s sea cows could not dive deep, so when the sea retreated and the temperature dropped, the number of suitable feeding sites for the animals decreased.”
“The starvation and the associated fragmentation of distribution possibly led to the origin of the small, separate refugia on the North Pacific islands for this mammal.”
“Approximately 5,000 years ago, the sea level stabilized; however, by this time, the range and Steller’s sea cow population size had significantly decreased.”
“Paleolithic hunter-gatherers also made their contribution to the extinction of the Steller’s sea cow, but, to be fair, only a few finds of the species have been described from dozens of Holocene coastal archeological sites in the Bering Sea region.”
“Finally, we conclude that the population on the Commander Islands, which was the last surviving Steller’s sea cow population, like the last woolly mammoth population from Wrangel Island, was subject to reduced genetic diversity and possibly, despite the size (around 2,000 animals), was on the verge of extinction by the time of the arrival of the Vitus Bering’s Great Northern Expedition.”
The results were published in the journal Nature Communications.
F.S. Sharko et al. 2021. Steller’s sea cow genome suggests this species began going extinct before the arrival of Paleolithic humans. Nat Commun 12, 2215; doi: 10.1038/s41467-021-22567-5
Source link: https://www.sci.news/genetics/stellers-sea-cow-genome-09569.html