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Secret of the black squirrel is revealed

Anglia Ruskin research shows that fur colour is caused by ‘faulty’ molecular switch

New research shows that a “faulty” switch coded in a squirrel’s DNA is the reason why some grey squirrels have black fur.

The research, led by Helen McRobie of Anglia Ruskin University and published by the journal FEBS Letters (Federation of European Biochemical Societies), reveals how a tiny molecular switch controls fur colour.  

Grey squirrels inherit a normal pigment gene from both parents (genotype E+E+), while black squirrels inherit a gene with a missing piece from both parents (EB EB).

McRobie, Senior Lecturer in Biomedical Science at Anglia Ruskin, said:

“If you look closely at grey squirrel hairs, they are not actually grey at all but are a combination of white, black and orange stripes. However, the hairs of black squirrels have no stripes; they are just plain black. 
“Our research shows that one hormone turns the switch on to make black fur, and a different hormone turns the switch off to make orange and white fur. So in the grey squirrel, as the fur is growing, the switch turns on and off to make the stripes. 
“However, in the black squirrel, because there is a piece of DNA missing, a piece of the switch is also missing. The first hormone that switches it on still works and black fur is made, but the second hormone that should switch off, actually switches on as well. The off switch fails and the black fur continues to grow.”

A similar mutation is found in the black jaguar and McRobie predicts that this is caused by the same thing – a broken molecular switch.

McRobie also leads the Black Squirrel Project, which is dedicated to recording sightings of black squirrels across the UK. 

The first black squirrel in the UK was spotted in Woburn, Bedfordshire in 1912 and 6,100 recordings, submitted by the public to the Black Squirrel Project over the last two years, show they have now spread as far as South West England, Wales and Southern Scotland.