Teeth from extinct Oregon sea otters reveal a northern kinship

Newly published research finds that Oregon’s sea otter population, which fur traders drove to extinction by 1911, was genetically linked to northern populations of the mammals.

The connection emerged from an analysis of ancient DNA from archaeological sea otter teeth collected in the 1960s and ’70s from two coastal archaeological sites near Seaside, as well as mineralized tooth plaque scraped off of historical museum specimens. Knowing their origin may help guide efforts to reintroduce the sea mammals to Oregon, said University of Oregon doctoral candidate Hannah P. Wellman.

Attempts to transplant sea otters from Alaska to Southern Oregon locations in the 1970s failed as the populations collapsed. It may be, Wellman said, that the sites were too far south to support the survival of northern otters whose genetics had not adapted to those environments.

“There are a lot of variables that go into reintroductions, and one of those is choosing the modern population from which to take the animals that will get reintroduced into the area lacking them,” Wellman said. “Ideally, the reintroduced animals should be as closely related as possible to the original population.”

The research, co-led by Wellman and Courtney Hofman of the University of Oklahoma, was detailed in a paper published online Dec. 2 ahead of print in the journal Proceedings of the Royal Society B.

In the study, mineralized tooth plaque, known as dental calculus, was removed from the teeth of 21 historical specimens at the Smithsonian National Museum of Natural History to obtain mitochondrial DNA and then compared to the DNA extracted from the teeth at the Oregon archaeological sites. The Smithsonian specimens came from various locations of the upper Pacific Northwest Coast and from fur trade-era otters from Oregon.

The resulting complete mitogenomes, which contain DNA passed on maternally, of individual otters were analyzed at the University of Oklahoma’s Laboratories of Molecular Anthropology and Microbiome.

The mitogenomes of Oregon’s extinct otters were compared with those of historical sea otters, dating from 1857 to 1983, from northern locations, as well as Russia, and with California otters. Oregon’s otters were found to be substantially different genetically than California otters and closely tied to historical clusters of otters from Washington state to Alaska.

“Using dental calculus is cool because it contains the DNA of the individual it is literally on, as well as the bacteria from the microbes that live inside its mouth,” Wellman said. “The plaque on my teeth right now contains a lot of bacterial DNA, but also DNA with my ‘fingerprint.’ Calculus also is ideal because you can remove it without damaging the teeth. It essentially enabled our research without any concerns about the destruction to rare specimens.”

Previous studies had suggested that Oregon was a transitional zone where the physical and genetic traits of the Southern California and Northern Alaska sea otter populations may have come together. The archaeological Seaside sea otters, Wellman said, cluster most closely with current Alaska sea otters, possibly reflecting the transition in genetic variation.

“As our study of mitogenomes shows, in the case of Northern Oregon it appears that the modern northern sea otter populations from Alaska, Washington and British Columbia are the most closely related,” Wellman said. “That suggests that it would be the most appropriate to reintroduce sea otters from those locations to the Seaside and other northern Oregon areas.”

It is possible, Wellman’s team noted, that animal and/or human behaviors influenced the makeup of the former Oregon otter populations, but ethnographic data suggests that local indigenous people were the source, rather than the recipients, of traded pelts.

Wellman’s research is supported by a predoctoral fellowship from the Smithsonian Institution, UO Graduate School travel awards and departmental funds. Her research is being shared with the Elakha Alliance, which is investigating the feasibility of reintroductions of sea otters to Oregon, as well as the Oregon tribes.

Madonna Moss, a professor in the Department of Anthropology and curator of zooarchaeology at the Museum of Natural and Cultural History, was a co-author. Others were Rita Austin and Nihan Dagtas of the University of Oklahoma, and Torben Rick, who earned a doctorate from the UO in 2004 and is now with the Smithsonian National Museum of Natural History.

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