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The discovery of several new ant zombie fungi got a lot of media attention over the last two weeks. The fungi take hold over ants and cause them to carry out specific actions beneficial to the propagation of the individual fungus infection.

I'm skeptical that a "higher order" animal, meaning a fish or a bird or a mammal, could be "zombified" in such a way that they carry out what amounts to programed, predictable, and sophisticated commands.

Has there ever been a case where a substance was introduced into the biology of a higher order animal, causing them to carry out these kind of actions? Doesn't have to be a fungus, even a manufactured and complex "poison" would count, but the outcome has to be a pretty complex action.

EDIT: substances that increase suggestibility don't count. After the substance is introduced, the subject needs to carry out the activity without any outside intervention.

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    Can you give any serious examples of people claiming fishes, birds, or mammals might be zombified by a fungus? Refuting generic claims is much harder than refuting precise claims. – Borror0 Mar 14 '11 at 19:42
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    "I'm skeptical that a "higher order" animal, meaning a fish or a bird or a mammal, could be "zombified""...I'm actually asking you to refute my claim that it CAN'T happen. So YOU fine ME some examples :) – Dogmafrog Mar 14 '11 at 20:08
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    My response might read a little unnecessarily snide. At the end of this article on the ants, biologybiozine.com/articles/strange-biology/…, they discuss implications for humans. I'm skeptical that the mechanism would be able to be as complex in humans or other high order organisms. That's where the question comes from. – Dogmafrog Mar 14 '11 at 20:26
  • I would suggest the elimination of the term "zombie." What you are looking for is a clear consistent pattern of behavior in infected individuals. Given that "higher-order" animals have more complex behavior, the subversion of one behavior would make the infected creature seem less zombified, and simply sick. – Ustice Mar 16 '11 at 18:35
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    Actually it's exactly that kind of complex behavior I'm looking for. Just being sick is too simple. In the ants, they are driven to find a specific plant (each fungus requires a different one), climb up, find a specific leaf at a specific angle, and attach themselves to it to die. That's a lot of unique actions. In rabies, there is an increased tendency to bite, but not so specific as "go to a certain area and only bite this specific type of animal in a specific place." – Dogmafrog Mar 16 '11 at 18:49
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Toxoplasma gondii have been reported to make rats less fearful of cats, and may even cause the rats to seek out cat-scented areas. Usually rats would avoid cat-scented areas, but the infection by the parasite can subtly change this behaviour without impacting other behaviours.

Changing this behaviour makes a lot of sense for the parasites as cats are its primary host and it can thereby increase its transmission rate.

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    Toxoplasma gondii is a quite common parasite, even in humans. Correlations with behavioural changes have been reported, e.g. people who suffer from schizophrenia are more likely to have been infected by the parasite. Here is an article that mentions it: economist.com/node/16271339 – Oliver_C Mar 14 '11 at 18:52
  • Good answer. The fungus in the ants seems to be quite a specific, ordered task (find a specific type of plant, climb up, find a leaf at a specific angle, anchor yourself and die). Any examples of that kind of specific behavior being created in higher order animals. This seems to be a preference, a bit more interesting than mad cows licking their skin, but does it qualify as complex behavior or just symptomatic tendencies? I think you're definitely on the right track, though. – Dogmafrog Mar 14 '11 at 19:50
  • There is an article stating that while 40% of the humans has this infection, the ratio is greater among people who suffered car accidents ncbi.nlm.nih.gov/pubmed/12095427 and here is is the media coverage guardian.co.uk/science/blog/2011/apr/12/… and here is a forum discussion about it fora.xkcd.com/viewtopic.php?f=9&t=70188 – Jader Dias Apr 14 '11 at 13:09
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    There is an interesting statement in that forum: "This isn't really new news; Toxo makes people more aggressive, more prone to bad decisions, and more likely to have sex with people. For what it's worth, it also makes rodents attracted to, instead of repelled by, feline urine." – Jader Dias Apr 14 '11 at 13:16
  • As of 2016, looks like the effects of Toxoplasmosis on human behavior have been, at least, overrated. blogs.discovermagazine.com/neuroskeptic/2016/02/20/… – hmijail mourns resignees Jun 24 '16 at 13:26
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Richard Dawkins dedicated his entire book The Extended Phenotype (which is an excellent read if you get the chance) to elaborate on the idea that your genes may express themselves not only as adaptations in your organism (a certain gene for longer arms or whatever), but possibly as adaptations in other, physically distinct organisms, via exactly the same mechanisms.

In his book, Dawkins alludes to the concept of parasites' intermediate and definite hosts, where a definite host is the host that eventually nourishes the parasite, and the intermediate host is only the means through which the parasite infects its definite host.

Although the book is riddled with examples, here's one that I think is especially instructive, as it deals with two parasites that exert different zombifying effects on the same host:

[Bethel and Holmes] studied two species of acanthocephalan worms, Polymorphus paradoxus and P. marilis. Both use a freshwater 'shrimp' (really an amphipod), Gammarus lacustris, as an intermediate host, and both use ducks as the definitive host. P. paradoxus, however, specializes in the mallard, which is a surface-dabbling duck, while P. marilis specializes in diving ducks. Ideally then, P. paradoxus might benefit by making its shrimps swim to the surface, where they are likely to be eaten by mallards, while P. marilis might benefit by making its shrimps avoid the surface.

Uninfected Gammarus lacustris tend to avoid ligth, and stay close to the lake bottom. Bethel and Holmes noticed striking differences in the behaviour of shrimps infected with cystacanths of P. paradoxus. They stayed close to the surface, and clung tenaciously to surface plants . . .

Shrimps infected by cystacanths of the other species, P. marilis, however, do not hug the surface. In laboratory tests they admittedly sought the lighted half of an aquarium in preference to the dark half, but they did not orient positively towards the source of light: they distributed themselves randomly in the lighted half, rather than at the surface. * The Extended Phenotype, Dawkins, p. 216-217

I realize you may not accept this 'shrimp' as a high order animal, but I think it is a useful example to sell in the idea of applying this zombiefying effect on one host, so as to be able to reach another. I wanted to sell in this idea, to see that this effect is not so uncommon, once you start to view the events in that light:

Dogs, when affected with rabies, will be driven to bite other dogs (well, other animals, really). A bland interpretation would be that the virus irks the dogs, and they're getting really aggressive about that. But consider that this tendency to bite others is the primary means through which the virus spreads. Could we not then agree that there is a direct appreciable selective pressure for this virus to exert this effect?

We know that this tendency is observed in rabies infected animals, and we can see that there is great evolutionary advantage to the rabies virus in it. I don't know what kind of scientific evidence you would need to be able to say that spreading the virus is the reason why the animals behave in this way, but I would certainly argue that that's the most plausible explanation.

Moving on along that line; we know that humans produce snot as an outlet for foreign bodies to leave our own body. But given that we have this mechanism up and running, wouldn't there be a huge selective advantage for the common cold virus to cause us to sneeze while in this condition? At this end, it becomes a bit sketchy, but I'd say drawing the line is single-handedly a matter of interpretation.

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  • Damn, beaten to the punch. ;-) – Konrad Rudolph Mar 16 '11 at 12:26
  • Rabies also makes animals fear water. I hear polar bears found inland are often rabid, for that reason apparently. – Brian M. Hunt Jun 10 '11 at 22:39
  • Science can't say "why" meaning "purpose"; but can say "why" (or more specifically, "how") meaning "what is the mechanism". – ChrisW Jun 28 '11 at 14:09
  • I don't think anyone has alluded to why in the "purpose" sense... – David Hedlund Jun 28 '11 at 15:47
  • I thought motives behind organism is out of skeptical scope? – user4951 Sep 12 '12 at 9:34
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I'm not sure if this will meet your criteria for "higher order" animals, but there is parasite known as Succulina which is known to invade certain species of crab, causing notable changes in the host's reproductive system and behavior.

The female Succulina will find a weakness in the host crab's shell and will sort of inject itself into the host. Once infested with this particular parasite, which happens to be a type of barnacle, the host is rendered infertile and its reproductive behavior is essentially hijacked so that the crab will abandon its own interest in reproduction in favor of nurturing the Succulina.

I have also read that if a male crab has been infected with the parasite, its behavior will be changed to that of a female, causing it to be mainly interested in nurturing the parasite. Here is a link to an abstract describing the effect, and one more link for those curious about the biology of the process.

They should be a good place to start.

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  • Thanks for the links, hadn't read about it. You're right, I kind of put crabs and ants in the same class, but it's still an interesting read and answer. – Dogmafrog Mar 14 '11 at 22:57
  • @Dogmafrog I'm not sure that crabs are "lower" than fish. – ChrisW Jun 28 '11 at 14:10
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Not sure if this meets the criteria exactly, however I present Dracunculiasis:

http://www.cartercenter.org/health/guinea_worm/central_african_republic.html

http://en.wikipedia.org/wiki/Dracunculiasis (I know it's a wiki page, however it has lots of links to valid references on it)

When the worm has matured and starts to break through your skin it causes a burning sensation to encourage the carrier to immerse themselves in water. Once this happens the worm releases lots of larva, infecting the water supply and restarting the life cycle.

The "zombie" behaviour in this instance is making the carrier seek out and immerse themselves in water as the larvae need water to be able to survive and infect new hosts.

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