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Parasite Leads to Cannibalism in Shrimp


Image credit: Alison Dunn and Mhairi Alexander, via Discovery News.

It is well-known that parasites could be capable of doing all kinds of strange and unpleasant things to their hosts, for example, they could make rats, and in some cases, humans become daredevils, force crickets to kill themselves, turn caterpillars into head-banging bodyguards as well as convert tiny ladybugs into zombie babysitters. Besides all these, scientists have now discovered that a common parasite could be able to drive cannibalistic behavior. However their research was targeted on shrimps rather than humans. In their opinion, it seemed impossible that a parasite would have impact on cannibalism within human beings. Such study has been made public in the latest issue of Royal Society Open Science.

Although cannibalism might be frowned upon in today’s society, it could be widely discovered almost everywhere in nature. Cannibalism has been recorded in more than 3,000 species, because such action of killing and feeding on conspecifics would bring out the different benefits, for example, it could enhance growth and survival as well as eliminate potential competitors. In addition, it could be much helpful for a population to keep growing when available resources begin to become insufficient. It is said that cannibalism is sort of double-edged sword, on one hand; it is good feast to gobble your own kind, but on the other, it could be riskful to acquire parasites, if the victim had been infected.

As it is clear that certain parasites are capable of having the huge impact on the behavior of their hosts, such as changing the rate of predation, scientists were eager to make sure whether parasitism would be an important factor in determining cannibalistic interactions. In order to know the reason better, a team of scientists from the University of Leeds, Queen’s University Belfast and StellenboschUniversity has initiated a study focused on examination of the effects of infection with a tiny common parasite named as Pleistophora mulleri. This organism is specific to a freshwater shrimp called Gammarus duebeni celticus, which is indigenous to Northern Irish waters,

The reason that they selected this pair for investigation is that more than 90% of this shrimp house the parasite. Based on strong evidence, this species are usually engaged in cannibalism. In addition, it is found that oral transmission is closely linked with the route of infection, more specifically, by the consumption of an infected shrimp, whether it is dead or alive.

During their study, scientists collected adult male and juvenile shrimps from a river in Northern Ireland and tried to identify whether or not they were infected so as to record their behavior towards one another. To the surprise, scientists discovered that infection with the parasite boosted the rate of cannibalism by adults towards juveniles, because parasitized shrimps eat twice as much of their own kind as uninfected individuals.

It is interesting with the choice given that uninfected adults were less possibly to cannibalize infected juveniles than uninfected individuals, while infected shrimp failed to avoid parasitized conspecifics, so it would be possible that they would have not any motive to do like this. On the other hand, uninfected individuals would gain benefit from this behavior, for it was meant that they would have the nutritional benefit from cannibalism, at the same time they would avoid infection as well.

As Mandy Bunke, lead author said, the parasite left a heavy burden on the host, since millions of them harbored in the shrimps’ muscle, dependent on the host for their food. Therefore it is probable that the enhanced requirement for food resulting from infection could be a driving force for cannibalistic behavior. Additionally, infection could be debilitating, thus weakening the ability of shrimps to take prey. In this way cannibalizing smaller conspecifics might be the easiest way to meet their demands for daily food.

Journal reference: Bunke, Mandy, et al. “Eaten alive: cannibalism is enhanced by parasites.” Royal Society Open Science 2.3 (2015): 140369.