Behavior-manipulating parasite could drive wildlife to lion den

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A popular feature of house cats is how easily they poop in the same relatively easy-to-clean box day in and day out. However, cat owners should be careful to regularly change the cat litter and wash your hands thoroughly after doing so. This is because cats (not just domesticated felines, but also wilder felines like lions and tigers) are the only ones known. definitive hosts the protozoan parasite Toxoplasma gondii.

Being a definitive host means that the parasite, which in this case spreads through feces, can only sexually reproduce in a cat. But that does not limit its infectivity to our kitten companions; it can also infect all kinds of other animals, of which at least a third of human population. “It infects almost all warm-blooded organisms,” says Ajai Vyas, associate professor at Nanyang Technological University in Singapore and an expert in neuroscience and parasitology.

In non-definitive or intermediate hosts, T. gondii is famous for manipulate behavior. This is particularly well studied in rodents, where the parasite reduces its host’s innate fear of cat odors. It is believed to be an adaptation that increases the likelihood that a rodent host will be eaten by a cat, allowing T. gondii the chance to reproduce.

However, the mechanism behind T. gondiimanipulation tactics remains mysterious. Some argue that the parasite takes hold in certain areas of the brain and affects neurons there, while others postulate that it interferes with dopamine signaling more generally. A third hypothesis states that the manipulation does not require T. gondii be present in the brain, but is instead initiated by hormonal interactions.

Walk on the wild side

Although T. gondiiThe behavioral manipulation of and its underlying mechanisms are the subject of active study, much of the research so far has focused on laboratory animals. One of the first studies, published in 2000, purposely used rats with wild heritage, but work since has tended to focus on lines bred in the laboratory.

Lab environments have the advantage of being a lot simpler than natural ones, but “obviously there’s a problem there, and the problem is that the lab isn’t biology,” says Vyas. . “But on the other hand, in nature… you are limited to observational studies, case-control studies, longitudinal studies, but never to experimental manipulation.”

T. gondii building daughter scaffolds in the mother cell. (Credit: Daniel Mietchen / CC-BY-4.0 / Wikimedia Commons)

A handful of studies have investigated the behavioral effects of T. gondii on wild intermediate hosts; these include work on wild rodents as well as sea ​​otters, chimpanzees, and even human (Yes he can affect our behavior). However, a 2021 study extended the research to new territory: spotted hyenas.

This new study, led by Eben Gering of Nova Southeastern University in Florida and Zachary Laubach of the University of Colorado Boulder, not only shows that T. gondii increases the audacity of small hyenas towards a cat – in this case, the lions – but also this infection increases the risk that a hyena is killed by a lion. This is the first known evidence that the reduced fear of cats caused by T. gondii in wild hosts comes with a predation cost.

Track footprints

“This is a very important step in Toxoplasmliterature, ”says Vyas, because“ predation only occurs in a natural setting. You can’t put a dolphin in a tub and study swimming behavior.

Unfortunately, while the study used a wealth of data collected over three decades and was statistically powerful, it lacks the experimental control to truly confirm a relationship between T. gondii lion infection and death. However, her evidence of a potential association is still monumental and Vyas takes it as a sign for further investigation.

“What I would really like to see is a relationship between the mechanisms… down to the behavior,” he says. “From the brain and hormones. Vyas is interested not only in the parasite and its host, but also in the impact of their relationship on entire ecosystems. “What are the footprints of these [brain and hormone] changes within ecological communities? “

As for our relatively small pets, there is less to worry about. While some studies suggest that T. gondii can have subtle effects on our own psychomotor personalities and performances, humans are dead end hosts; there is an almost zero chance that a domestic cat will eat its owner, regardless of the infection status. Still, it’s probably a good idea to clean that litter box out anyway.


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