Bears that eat human ‘junk food’ may hibernate less | Science News for Students

Bears that eat human ‘junk food’ may hibernate less

And that might risk their aging faster at the cellular level, a study concludes
May 1, 2019 — 6:45 am EST
black bear trash

This black bear is finding food at a garbage dump. The more a black bear snacks like a human, the more likely that bear is to skimp on hibernation, a new study says. And shorter hibernation might accelerate aging at the cellular level.

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Mama bears may need to raise their snouts and join the chorus protesting junk food. 

Bears are scavengers. And they’ll eat human food when it’s available. But in a new study, the more sugary, highly processed foods that 30 female black bears ate, the less time those bears were likely to spend hibernating. In turn, bears that hibernated less tended to score worse on a test for aging at the cellular level. 

Researchers published the findings February 21 in Scientific Reports.  

The new research grew out of an earlier project to see what wild black bears across Colorado were eating, says Jonathan Pauli. He’s a community ecologist at the University of Wisconsin–Madison.

While a Ph.D. student at the school, wildlife ecologist Rebecca Kirby checked diets from hundreds of bears across the state. Hunters there are not allowed to set out bear bait, such as heaps of doughnuts or candy. That means the animals’ exposure to human food comes mostly from scavenging.

When bears eat more processed foods, their tissues pick up higher levels of a stable form of carbon known as carbon-13. It comes from plants such as corn and cane sugar. (These farmed plants concentrate the air’s normally sparse amounts of carbon-13 as they build sugar molecules. This is different from what happens in most wild plants in North America.) 

The researchers looked for the telltale forms of carbon in an earlier study. They found bears in some places scavenging a “really high” share of people’s leftovers. Sometimes, these leftovers could make up more than 30 percent of a bear’s diets, Pauli notes.

In the new study, Kirby looked at the impact of diet on hibernation. Bears typically slumber four to six months, during which female bears give birth. Kirby and her colleagues focused on 30 free-roaming females around Durango, Colo. These bears were monitored by the state’s parks and wildlife department. The team first tested bears for carbon-13. They found that the ones that ate more human-related foods tended to hibernate for shorter periods.

Signs of age

Studies in smaller mammals hint that hibernations might delay aging. If true, shortening these seasonal slumbers might have a downside for the bears. 

To measure aging, the researchers tested for relative changes in length of telomeres (TEL-oh-meers). These repeating bits of DNA form the ends of chromosomes in complex cells. As cells divide over time, telomere bits can fail to get copied. Telomeres can thus gradually shorten. Some researchers have proposed that tracking this shortening can reveal how quickly a creature is aging. 

In the new study, bears that hibernated for shorter periods tended to have telomeres that shortened more quickly than those of other bears. This suggests the animals were aging faster, the team says.

Free-ranging bears didn’t always cooperate with Kirby’s needs for several kinds of data. And so she does not claim to have made a direct and “definitive” link between what bears eat and aging. So far, Kirby (who now works for the U.S. Fish and Wildlife Service in Sacramento, Calif.) calls the evidence “suggestive.”

Using additional methods to measure telomeres could help clarify what is going on at the level of cells, says Jerry Shay. This telomere researcher works at the University of Texas Southwestern Medical Center in Dallas. Still, Shay muses, the idea of linking more human food to shortened bear hibernation and faster cell aging “may be correct.”  

Power Words

(more about Power Words)

atmosphere     The envelope of gases surrounding Earth or another planet.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. 

chromosome     A single threadlike piece of coiled DNA found in a cell’s nucleus. A chromosome is generally X-shaped in animals and plants. Some segments of DNA in a chromosome are genes. Other segments of DNA in a chromosome are landing pads for proteins. The function of other segments of DNA in chromosomes is still not fully understood by scientists.

diet     The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. (verb) To adopt a specific food-intake plan for the purpose of controlling body weight.

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

ecology      A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

hibernation     A state of inactivity that some animals enter to save energy at certain times of year. Bears and bats, for example, may hibernate through the winter. During this time, the animal does not move very much, and the use of energy by its body slows down. This eliminates the need to feed for months at a time.

link     A connection between two people or things.

mammal     A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

processed foods     Foods purchased from a grocery story that are substantially different from the raw materials that went into them. Examples include most foods that come in cans, bottles, boxes or bags. Examples include breakfast cereals, frozen pizzas, canned tuna, jars of spaghetti sauce and dill pickles.

scavenger     A creature that feeds on dead or dying organic matter in its environment. Scavengers include vultures, raccoons, dung beetles and some types of flies.

telomere     A natural protective “cap” on the ends of chromosomes, made by successions of a six-nucleotide sequence of chemicals. This chemical sequence is found only on the ends of chromosomes. It’s known as TTAGGG, where each T corresponds to a molecule of thymine, each A is a molecule of adenine and each G is a molecule of guanine. Over time, telomeres shorten as they cell they’re in copies itself. If the telomere length gets too short, the cell stops dividing and dies.

tissue     Made of cells, it is any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.

U.S. Fish and Wildlife Service     A research agency of the U.S. Department of the Interior, it was created in 1871 as the U.S. Commission on Fish and Fisheries. Fourteen years later, it acquired an office of ornithology (the science of birds). In 1905 it was renamed the Bureau of Biological Survey. It now has authority for research on and the conservation of land-based species, of freshwater species and of migratory birds.


Journal:​ ​​R. Kirby et al. The cascading effects of human food on hibernation and cellular aging in free-ranging black bears. Scientific Reports. Published online February 21, 2019. doi:10.1038/s41598-019-38937-5.