Tiny Island Foxes Are Treading in a Shallow Gene Pool

April 25, 2016 | Erica Tennenhouse

Island fox (Urocyon littoralis)

This might be the least genetically diverse species in the world

Six of California’s Channel Islands are home to a dwarf fox species, only two-thirds the size of the mainland gray fox from which it is descended.

Not only are the Channel Island foxes small, but so are their population sizes. And though they have persisted for thousands of years, scientists have wondered if their small numbers might make these island foxes genetically unhealthy and susceptible to population crashes.

A group of researchers sequenced the genome of this island species and discovered a surprising lack of genetic variation, according to results published in the journal Current Biology.

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"We find a dramatic reduction of genetic variation, far lower than most other animal species," Jacqueline Robinson of the University of California, Los Angeles (UCLA) said in a statement.

Particularly alarming was one population on San Nicolas Island, found to have genetic variation an order of magnitude lower than any known wild animal, including the severely endangered African cheetah, mountain gorilla, and Tasmanian devil, she said.

Normally, populations use their genetic variation to respond to changing environmental variables — if a particular trait is not working out, other gene variants give populations the ability to respond and evolve.

On the other hand, the unusually low genetic variation found in the Channel Island foxes — described by the authors as “genomic flatlining” — is normally expected to lead to rapid extinction.

"The degree to which the San Nicolas foxes have lost genetic variation is remarkable, upholding a previous observation that they may be the least genetically variable population of wild animals known," said Robert Wayne, also of UCLA. "It suggests that under some conditions, genetic variation is not absolutely essential for the persistence of endangered populations."

Although the foxes showed incredibly low overall genetic diversity, they also showed high variation in some genes that are thought to be harmful. “The island fox populations suffer from both a lack of genetic diversity and the accumulation of damaging genetic variants, which is likely to worsen over time," said Wayne.

The researchers assert that these new findings should be considered in light of a recent push to remove the Channel Island foxes from the endangered species list.

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