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Tommy Leung
Parasitologist, Evolutionary Biologist, Researcher, Lecturer
Parasitologist, Evolutionary Biologist, Researcher, Lecturer
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Tommy's posts

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Of Chimps, Leopards, And Toxoplasma
Some of you may be familiar with the story about a little cat parasite call Toxoplasma gondii. It seems to be able to alter rodent behaviour so that they are more likely to be eaten by a cat, but it can also infect humans (and any warm-blooded vertebrate animal) and supposedly mess with human behaviour as well. Spoooooky. At least that's how the story goes. Like any other story, there is some grain of truth to it, but it is buried within a whole mass of (more sensationalised) dross. Any studies into Toxoplasma and host behaviour manipulation has the potential to go viral as it includes all the elements that makes a good headline - it contains cats, brain parasites, and zombies (in the form of host behaviour manipulation).

The literature on Toxoplasma and host behaviour is MASSIVE - some of it is good science, others are more like tabbies dressed as tigers. But for this post, I'm going to focusing on one story within a larger narrative, I want to talk about a paper recently published in Current Biology which had whipped the media into a frenzy (again) about how human behaviour is affected by Toxoplasma. http://www.cell.com/current-biology/abstract/S0960-9822%2815%2901517-1

Here's a tl;dr version of the study. The study found that compared with uninfected chimps, chimpanzees infected by Toxoplasma are not as averse to the odour of leopard (their natural predator) urine. The researchers concluded that this is because Toxoplasma is manipulating the chimps' behaviour so that they will be more likely to be eaten by a leopard (the final host for Toxoplasma are felines).

1) While the media coverage seems to be focused on how the parasite affects human behaviour, this experiment was done on chimps, and the media is extrapolating the conclusion of that study to humans. Humans and chimps may be genetically similar on some level, we have been separated by 5-7 million years of evolution, and our ancestors evolved in very different environments. There are some very key differences in the behaviour of chimps versus humans.
 
2) The study was not only correlative in nature, it was based on testing chimps for presence of Toxoplasma antibodies - not the parasites themselves, just a potential indicator of the parasites presence (having antibodies for something doesn't guarantee the presence of the said thing in the body). The researchers didn't confirm the presence of the parasites themselves. I understand they can't exactly do the latter for ethical reasons, in which case, maybe don't cannonball your way into such sensationalised conclusions?

3) The study tested how chimps response to the odour of urine and other big cats - the question is, just how much of a role does the sense of smell play in chimpanzees' predator avoidance repertoire? There is surprisingly little research on that. Is the sense of smell that important for predator avoidance compared with their other senses? Also, considering that chimpanzees are social animals, they would also rely upon other individuals in the group to warn of the presence of predators - you can't consider the vulnerability of a chimp to predation without the context of its social structure.

4) They mention potential behaviour variations between individuals (i.e. personalities) which may account for different level of aversion towards leopard urine odour which are pre-existing, regardless of the parasite. Good. But then, they just dismiss that possibility outright, by citing a single study that has found Toxoplasma is associated with disrupted fear response - in rat. Studies in other animals have shown that propensity for "recklessness" varies between individuals, even without the influence of parasites. So they're essentially saying Toxoplasma is the only possible explanation for why those chimps behaved slightly differently (in one aspects - response to leopard urine odour), even after bringing up the possibility that these behaviour variations exists regardless of parasitism, and discounting the dozens of other equally valid potential explanations. Not Wow.

5) Furthermore, when I dig into the methods, I found that the study was conducted on captive chimpanzees. Captive animals (especially behaviourally complex animals such as chimps) are known to exhibits behaviour which deviate significantly from their wild relatives. So we have no way of establishing whether such behaviour is representative of how they would behave in a natural setting (let alone extrapolating it to humans as the media has done). Once again, I understand that it would be extremely difficult to conduct such a study on wild chimps, in which case, the point I bring up in (2) still applies - don't jump to such sensationalised conclusions

6) Given the correlative nature of the study, we have no way of establishing how these chimps would have behaved before getting infected with Toxoplasma. So you can't rule out that maybe the chimps that behaved "oddly" are simply more likely to pick up Toxoplasma. They did mention this possibility, but they dismissed it just as quickly in the same manner as I described for (4).

7) The paper has 10 references in total (the supplementary material has 2 additional reference, but they were for methodological techniques), but did not cite a review recently published in 2014 in Advances in Parasitology which discussed at length the wide array of inconsistencies and seeming contradictory results from rodent-toxoplasmosis behavioural studies.
https://books.google.com.au/books?hl=en&lr=&id=ftnEAgAAQBAJ&oi=fnd&pg=PA109

And that's all I have to say about that. Peace out.

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The Living Dead Are Biting Daisies
I've written a new Parasite of the Day blog post! This one is about zombie beetle fungus that takes over its host in both body and mind. Not only does its make its host climb onto a flower and bite down, even after the host has die, the fungus has one more trick for making the dead beetle unfurl its wings. To find out more about this body-snatcher fungus, follow the link below.

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Worms, Germs, And Toxins
I've written a new Parasite of the Day blog post! This one is about Steinernema carpocapsae - a parasitic nematode that lurks in the undergrowth and kills insects using an arsenal of toxins and bacterial symbiont. To find out more about this parasitic killer, follow the link below.

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Tongue-Biter And Monster Girls
Those of you who follow my work online will also know that aside from writing about new parasitology research on the Parasite of the Day blog, I also have this habit of drawing Parasite Monster Girls : http://goo.gl/VLxB9o
In a move which some people would describe as "It's about time", I have drawn the infamous tongue-biter louse (actually a parasitic isopod) as a Parasite Monster Girl - meet Cynthia the Cymothoid Monster Girl. I also wrote briefly about parasitic isopods from the Cymothoidae family, so to see Cynthia in her full glory and learn a bit about parasitic isopod, follow the link below.



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Red Flowers And Parasitic Tubers
I've written a new Parasite of the Day post! This one is about a type of parasitic plant from Central and South America that lives as a parasitic tuber attached to the roots of its host plant, and sprouts red flowers that pokes out the ground like mushrooms. To read more about this parasitic plant, follow the link below.

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Ectoparasites On Ectoparasites
I've written a new Parasite of the Day post! This one is about a type of fungus that live on the back of bat flies. The bat flies themselves are ectoparasites that live on bats, making that fungus an ectoparasite of an ectoparasite. To pre-empt the comments, yes I already know about (1) the Jonathan Swift quote about fleas on the back of fleas, and also (2) the Xzibit "Yo Dawg I hear you like..." meme. To read more about this ectoparasite of ectoparasites, follow the link below.

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Allosaurus Heavy Cruiser Hime
And now for something completely different. I've been working on a new piece over the last few weeks, and the result is an Allosaurus X Abyssals/Shinkaisei-kan hybrid. Follow the link for design notes and more information.

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A Fluke And A Hard Shell
I've written a new Parasite of the Day blog post! This one is about a parasitic blood fluke that lives in sea turtles. Infection by these blood flukes can result in a range of debilitating diseases in sea turtles, much of which comes from the eggs that these parasites lay in the hundreds and thousands. But how do turtles acquire such infections in the first place? The secret lies with some unusual gastropods call worm snails To find out more, follow the link below.

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Turtles All The Way Down
I've written a new Parasite of the Day blog post! This one is about a tiny parasitic copepod that lives on sea turtles and eats flakes of turtle skin. To find out more, follow the link below.

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Tapeworms And Monster Girls
Those of you who follow my work online will know that as well as writing about new parasitology research on the Parasite of the Day blog, I also have this habit of drawing Parasite Monster Girl : http://goo.gl/VLxB9o
So here's the newest Parasite Monster Girl from me - Tina the Tapeworm Queen (or "Cestusah" - like a medusa, but for cestodes). You might be wondering why it took me so long to get around to drawing a monster girl based on such an obvious, quintessential group of parasites - well technically, Tina here is a reboot of a PMG that I drew almost exactly a year ago. After a year of drawing PMGs, I've decided to revisit the idea of a tapeworm monster girl with my now more refined style based on a year's worth of accumulated experience and skills. So here she is - Tina - in all her tapewormy glory.

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