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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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Leaving Bears Bare
New guest post at the Parasite of the Day blog! This one has been written by Aidan McCarthy - a student from the 4th year class of the Applied Freshwater and Marine Biology' degree programme at the Galway-Mayo Institute of Technology in Ireland. This class is being taught by lecturer Dr. Katie O’Dwyer who has previous contributed guest posts to the blog. This post is about a lice that causes hair loss in bears - to find out more, follow the link below.

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The Ties That Bind
I've written a new Parasite of the Day blog post! This one is about a species of zombie ant fungus found in the forest of central Taiwan that uses sunlight as a cue to move its ant host into a prime position for it to sprout. Since this usually mean on the underside of a leaf, how does it fix the zombified ant in place? To find out more, follow the link below.

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Ceratosaurus Ne-class
And now for something completely different. I worked on some art during this week, and this is what happened. Follow the link for design notes and more information.

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Dead Bug Soup With Worms
I've written a new Parasite of the Day blog post! This one is about Heterorhabditis bacteriophora - a parasitic nematode that kills insects and turns their innards into a nutritious soup using a bacterial symbiont. But how can they keep away hungry predators that may wish to eat their dead host? To find out more, follow the link below.

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Flashy Body-Snatchers, Parasite Services, and Intrepid Journeys
I have written an end-of-2016 round-up post for the Parasite of the Day blog! A look back on 2016 and some of the fascinating parasite stories that were covered on the blog this year. From vampire mites to hitch-hiking lice to zombie snails and tongue flukes, you'll find links to them all in the post below!

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Zombie Moths And Monster Girls
Those of you who follow my work online for long enough this year will know whenever I write a new Parasite of the Day blog post, there's a chance that I'll follow it up by drawing another Parasite Monster Girl : http://goo.gl/VLxB9o
Meet Akane the Cordyceps-infected Moth Girl based on moths infected by the anamorph form of Cordyceps tuberculata (also previously known as _Akanthomyces pistillariformis _). For more details about the parasite-host system that Akane is based on, follow the link below.

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Zombie Snail Parasite Party
I've written a new Parasite of the Day blog post! This one is about Leucochloridium paradoxum - the parasitic fluke also known as the infamous "zombie snail parasite". But L. paradoxum is not the only "zombie snail parasite" out there which produce those signature pulsating brood sacs. To find out more, follow the link below.

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Fishing For Parasites
I've written a new Parasite of the Day blog post! This one is about how commercial fishing and aquaculture is facilitating the life-cycle and transmission of a parasitic fluke. To find out more, follow the link below

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Romancing the Tyrant
And now for something completely different... I wrote a review of the manga "My Girlfriend is a T-Rex*" volume 1 for the *Love in the Time of Chasmosaurs" blog - check it out!
*Yes, I know the proper way to abbreviate Tyrannosaurus rex is T. rex - but that is the series’ official title.
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