European beavers mate for life, and remain faithful to their partners. North American beavers? Not so much. What's the reason behind this discrepancy ... and which of the two beaver species has the greater advantage?

A new genetic study headed up by Pavel Munclinger, a professor in the Department of Zoology at Charles University in Prague, Czech Republic, looked at a number of European beaver colonies living around Kirov, Russia. What was discovered, BBC Earth reports, is that "in every colony, all the offspring belonged to both of the parents. None of them had been fathered by males from elsewhere."

This would not have been the case if the test pool of beavers had been hanging out somewhere in North America; earlier research found that "the 'father' of a pair of young was unrelated to at least one of them about half the time."

There are reasons why the North American beavers aren't as loyal as their European counterparts:

Their social habits are different. American beavers are less aggressive than European beavers. Their populations are also larger and more tightly-packed, at least in some areas.

Cheating does have its advantages. If a mother mates with a healthier male than her main partner, she can pass better genes onto her young.

But there are also advantages to staying loyal. "Genetic monogamy lowers the risk of parasite transmission," says Munclinger. "It also lowers the risk of partner desertion, which is very important in species with extensive parental care of both sexes."

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So, both lifestyles are solid, it seems, at least until someone proves that beavers are capable of getting jealous.

As an aside, the BBC story names the few other mammals known to mate for life, and (duh) humans ain't on the list. Besides beavers, it consists of prairie voles (wee rodents for whom "for life" means but a year or two) and night monkeys.

Photo by Flickr user finchlake2000.

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