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For many years, Grey Squirrels (an introduced North American species) has been driving out the indigenous Red Squirrel over most of mainland Britain. But now it is reported that a mutant black variety of the Grey Squirrel is threatening to displace the Greys. Apparently, the black ones have higher testosterone levels, are more aggressive, and more attractive to the lady squirrels. (Don’t worry, our White Nationalist readers, this isn’t a parable. I think.)
Joking apart, the real interest of this is that it seems to be a case of a single mutation with a relatively conspicuous phenotypic effect having a strong evolutionary advantage, somewhat contrary to Darwin/Fisher orthodoxy. There is of course another example in the case of industrial melanism.
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How much of this is just the usual shoddy (slightly sensationalist) British journalism and how much actual fact? Black color morphs are fairly common in grey squirrel populations in North America, but they’re never more than 10% of the population. The Washington, DC area has a higher concentration of black squirrels, and while I don’t have any documentation on it, I estimate it at no more than 10% of the total squirrel population. They’ve been stable at those levels for decades. Olney, ILL has a stable population of a white color morph. Don’t know why the British black color morphs have so much advantage over the greys when their American cousins don’t.
This is massively anecdotal, but awhile back I was watching the squirrels who had taken over my brother’s bird feeder, and a red squirrel was chasing a lot of bigger grey squirrels all over the place. It would chase one of them fifteen feet up a tree and go back to the bird feeder and chase away another one. It was very high testosterone but on the other hand, wasn’t able to eat much.
I’m not completely sure that it even was a red squirrel. For all I know there are reddish gray squirrels. But it was reddish.
It’s true. We noticed a few years ago that black squirrels were beginning to take over in North Cambridge. Whether it is coincidence that all this is happening near the home of the double helix……..
It is interesting that the black squirrels show a link between eumelanin and testosterone/aggression. This also seems to hold true in humans.
the real interest of this is that it seems to be a case of a single mutation with a relatively conspicuous phenotypic effect having a strong evolutionary advantage, somewhat contrary to Darwin/Fisher orthodoxy.
It’s what you get out of Orr’s model, though. There’s one mutation that has a host of beneficial effects, and few mutations that have lesser effects, and scores of mutations that have tiny effects. A geometric distribution.
There was a recent study on sticklebacks (iirc) providing data for this theory. One mutation affected quite a few body part positions.
If testosterone is involved, this also sounds like it may resemble the Common Side-blotched Lizard, the one that comes in three color morphs that play paper-rock-scissors. The orange one is the testosterone-addled morph there.
So you could either see oscillations between the two morphs (if Red really is all but gone), or a monotone increase in Blacks up to a less-than-fixation point. Frequency-dependence.
Red is not a morph. Red is a completely different species.
to-may-to, to-mar-to. 😉 To determine whether there will be co-existence or displacement, we can treat it as a morph.
Whether the ‘gray’ squirrels are gray or black makes no difference – they’re still carriers of the virus that is lethal to the reds.
The factor that is involved in the destruction of the red squirrels has absolutely nothing to do with color or potentially-associated traits.
England´s industrial blackness is a thing of the past. I have recently toured England and the air, even in London, is clear and pure. Black fur would give no competitive edge to male squirrels, except if the females suscribe to black is beautiful.
From where I’m sitting (51.8468N, 0.4946W) in my office overlooking our garden in South Bedfordshire, it seems that the greys have almost driven out the blacks over the last two years, and also that the greys are conspicuously larger and more aggressive than the blacks. It’s a pity, because I’d never seen a black squirrel before we came to this house in 2006, and prided myself in having an unusual animal in the garden. But this is just anecdotal evidence. I’m sure the front line ebbs and flows, and even the squirrel generals have little idea which way the war is going.
“I’m not completely sure that it even was a red squirrel. For all I know there are reddish gray squirrels. But it was reddish.”
This was the scots-irish strain of squirrels. Born fighting.
I heard that a female squirrel broke her ankles in a paw-race with a large brown squirrel and had to be put down and couldn’t run for squirrel-president. Or was that shoddy sensationanalistic reporting?