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UW Researchers Part of Study that Finds Sea Otters' Use of Tools Not Linked to Genetics

March 30, 2017
sea otter on back in the water, holding a clam
A sea otter floats on its back while eating a clam from a shell. UW researchers Holly Ernest and Roderick Gagne contributed to a paper that was recently published in Biology Letters. The new study reveals that, unlike bottlenose dolphins, California sea otters’ frequent use of tools has little to do with genetic ties and more to do with ecological conditions. (Jessica Fujii Photo)

Sea otters have the distinction of using tools, such as rocks, to break open hard-to-access food sources. A new study -- in which two University of Wyoming researchers participated -- reveals that, unlike bottlenose dolphins, California sea otters’ frequent use of tools has little to do with genetic ties and more to do with ecological conditions.

“Within marine mammals, the best examples of tool use are sea otters and Indo-Pacific bottlenose dolphins. In both species, tool use is not implemented by all individuals even within a population,” says Roderick (Erick) Gagne, a postdoctoral research associate in UW’s Department of Veterinary Sciences. “Genetic analyses of the bottlenose dolphins revealed that tool use was strongly related to a single matriline (lineage from the mother’s family tree line) and that tool-use transmission is likely cultural. In sea otters, however, we found no association between relatedness and mitochondrial haplotypes (part of the DNA genome inherited from the mother) with tool use. Instead, our work suggests a predisposition of all sea otters to use tools when faced with certain ecological conditions.”

A paper, titled “Mitogenomes and Relatedness Do Not Predict Frequency of Tool-Use by Sea Otters,” appeared in the March 22 issue of Biology Letters. Biology Letters is a broad-interest journal publishing short, highly innovative, cutting-edge research articles and opinion pieces across the biological sciences.

Holly B. Ernest, a UW professor of wildlife genomics and disease ecology, and the Wyoming Excellence Chair in Disease Ecology, also was part of the larger study commissioned by the Smithsonian Conservation Biology Institute.

“I generated (sea otter) DNA data over 10 years of work with my team at my University of California-Davis lab prior to coming here for the Excellence Chair,” says Ernest, who established the Wildlife Genomics and Disease Ecology Lab at UW. “I recruited Erick here to Laramie to conduct statistical genetic analysis for this paper and a range-wide study that will come out later. We’re very excited about this work.”

The sea otter microsatellite DNA data spans 12 years (including work in Ernest’s UW lab) of sampling and represents more than a decade-long effort to generate this large data set for southern sea otters. The larger set of data (nearly 1,000 otters) is in analysis and will be used to answer important evolutionary, ecological and conservation questions regarding southern sea otters.

Sea otters use rocks or other hard objects to break open well-armored prey, such as abalones, clams, crabs, mussels, marine snails and urchins. In one video captured during the research, a sea otter banged a snail against the side of a boat docked in a harbor.

“It is so interesting that so few animals do this; dolphins and otters are the only marine mammals that do,” Ernest says. “Some birds, such as crows, use tools. Chimpanzees do, too.”

During the study, individual sea otters were captured and tagged from 2000-2014 along the California coast. Focal animal sampling was used to record foraging data on individual otters. For each feeding dive, researchers recorded whether or not sea otters captured prey; what type of prey; and the presence or absence of tool use by the sea otters.

Individual sea otters were considered frequent tool users if they used tools for at least 40 percent of observed food captures. Individual sea otters belonging to every diet type sometimes used tools, but tool use is most frequent in those sea otters that prey heavily on snails. Abalone captures were excluded from analyses because it could not be consistently determined whether sea otters used tools to obtain abalone. Dependent otter pups were not considered in any analyses.

The paper concluded the lack of genetic association with tool use in sea otters, compared with dolphins, may result from the length of time each species has been using tools. While tool use by dolphins is thought to be a recent innovation, it is likely a much older behavior in sea otters. This is supported by evidence that all young sea otters appear innately predisposed to using tools.

“With dolphins, it (tool use) seems to be a learned behavior. With otters, it’s a more innate. It’s an ancient behavior,” Ernest says.

“All sea otters are able to do this,” adds Gagne, who is originally from Philadelphia, Pa., but conducted his graduate studies at Tulane University. “One of our hypotheses is we think they have been able to use tools longer than dolphins.”

In terms of how long otters have been using tools, Ernest and Gagne do not have a precise date. Studying skeletal fossils of ancestors of sea otters that provide limited evidence to suggest tool use, Gagne surmises tool use could date back millions of years.

In addition to Ernest’s and Gagne’s contributions to the paper, the overall study required collaboration across many research institutions to combine multiple lines of genetic data with ecological data on sea otter diet preference and use of tools. The lead author, Katherine Ralls, at the Smithsonian Center for Conservation Genomics, designed the study and organized a research team. Complete mitochondrial genomes were sequenced by Nancy Rotzel McInerney in the lab of Jesus Maldonado at the Smithsonian Institute. Sea otter tool use and diet type data were collected and analyzed by Tim Tinker at the University of California-Santa Cruz, in collaboration with Jessica Fujii at the Monterey Bay Aquarium.

The paper has already received significant international coverage, including from the BBC and Science News.

Sea Otter Video (Sophia Lyon Video)

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