Rats Manipulated to be Attracted to Cats
By RICHARD DAWKINS - RICHARDDAWKINS.NET
Added: Sun, 19 Aug 2012 15:47:49 UTC - An RDFRS Original
I devoted a whole chapter of The Extended Phenotype to parasites manipulating their hosts to assist the parasites into the next stage of their life cycle. There's a large literature on this, which I interpret as parasite genes finding phenotypic expression in host bodies. The logic of gene/phenotype causation is the same, whether the genes are foreign or "own" genes. Indeed, part of my aim was to break down the conceptual barrier between "own" and foreign genes. There's an abbreviated version of the argument in Chapter 13 of the Second Edition of The Selfish Gene.
Given all that, I reproach myself for missing a lovely paper in the Proceedings of the Royal Society 2000, by a group of Oxford colleagues, which is a perfect illustration of the principle.
The protozoan parasite Toxoplasma gondii, which lives inside the cells of its host, has cats as its definitive host, and rats as intermediate host. It leaves the cat in the faeces, from where it may then be ingested by a rat. It travels from rat to cat when an infected rat is eaten by a cat.
Natural selection would therefore favour Toxoplasma genes that change the behaviour of the rats they inhabit, making them more likely to be eaten by cats. This could be achieved as a "boring byproduct" of simply making the rats sick, so that they are less adept or speedy in running away from cats. However, Berdoy, Webster & Macdonald found something much more interesting. They showed experimentally that
although rats have evolved anti-predator avoidance of areas with signs of cat presence, T. gondii’s manipulation appears to alter the rat’s perception of cat predation risk, in some cases turning their innate aversion into an imprudent attraction.
It's a beautiful example, which I wish had been available when I wrote The Extended Phenotype. The altered rat behaviour is an adaptation for the benefit of T.gondii genes, specifically those T.gondii genes that express themselves in the rat brains that they inhabit.
I repeat, it is especially pleasing that this effect is achieved, not in a boring way simply by making the rats sick and therefore more sluggish in escaping from cats. Indeed, they seem to have no obvious effect on the general health of rats. Their effect is a specific manipulation of rat behaviour vis-a-vis cats. It's as though they are pulling puppet strings in the rat's brain. A neurophysiologist would not be surprised to discover a way of doing exactly that, either with micro-electrodes in rat brain cells or with drugs. Or geneticists could do it by genetic manipulation of rat genes. It seems that natural selection, working on protozoan genes, has achieved exactly the same thing.
- - TAM 2012 - JREF Comments
R. Elisabeth Cornwell at TAM 2012 - Social Networks: Civilizing the Future
- - The Royal Society Comments
Research suggesting that grey parrots can reason about cause and effect from audio cues alone- a skill that monkeys and dogs lack- is presented in Proceedings of the Royal Society B today.
Thomas H. Maugh II - LA Times Comments
Modern culture emerged in southern Africa at least 44,000 years ago, more than 20,000 years earlier than anthropologists had previously believed
Michael Balter - Science Comments
Studies to examine how children learn tasks that are not obvious and can even be counterintuitive.
Ker Than - National Geographic News Comments
After a poacher's snare had killed one of their own, two young mountain gorillas worked together Tuesday to find and destroy traps in their Rwandan forest home
Michael Balter - Wired Science Comments
New studies on volcanic glass show that a volcanic eruption once thought to be blamed for the demise of Neanderthals occurred after they were already gone.
MORE BY RICHARD DAWKINS
Richard Dawkins - RichardDawkins.net Comments
No Precedent? Then Set One?
Richard Dawkins - for the Press and... Comments
I was invited several months ago to speak at the Faclan Book Festival in Stornoway and I was delighted to accept, as I have a great affection for the Highlands and Islands but have never visited Lewis and have heard such good things about its beauty and about the friendliness of the islanders.
Richard Dawkins - RichardDawkins.net Comments
It's What Moral Philosophers Do
Richard Dawkins - - Comments
Freethinkers, atheists, agnostics, secular humanists – whatever name non-believers go under, they are not America’s most popular minority.
Richard Dawkins - Prospect 188 Comments
Richard Dawkins's review of The Social Conquest of Earth, by Edward O Wilson (WW Norton, £18.99, May) - (with Polish translation)
Richard Dawkins - RichardDawkins.net 174 Comments
[Journalists] seem to feel let down when they discover that the real people aren't anything like the way they so relentlessly portray us; as if, since they've gone to the trouble of inventing extravagant caricatures of us, we should at least have the decency to live up to them in real life.
Also in Polish