A terrifying parasite can turn its shrimp host into a raging cannibal that consumes its taboo meal at an alarming speed.
A team of researchers looked at how the tiny parasite Pleistophora mulleri increases cannibalism among shrimp indigenous to the waters of Northern Ireland, the University of Leeds reported. The infected Gammarus duebeni celticus shrimp also proved to take much less time to consume their victims than non-infected shrimp.
"Cannibalism is actually fairly common in nature. Our work is the first study to ask if cannibalism is affected by being parasitized," said Alison Dunn, Reader in Evolutionary Biology in the University of Leeds' Faculty of Biological Sciences, who led the study.
The researchers noted it is common for adult Gammarus duebeni celticus shrimp to consume juveniles, but shrimp infected with the parasite consumed twice as many preys of their own species.
"Although the parasite is tiny-similar in size to a human red blood cell-there are millions of them in the host muscle and they all rely on the host for food. This increased demand for food by the parasites may drive the host to be more cannibalistic," said Mandy Bunke, a PhD student at the University of Leeds who was the key researcher on the study.
The parasite takes over large areas of the shrimp's muscle, giving the normally transparent critters a "chalky" appearance. Past studies have shown infected shrimp are actually able to catch and eat less prey of other species, suggesting cannibalism is the only way for them to survive. The recent study also found uninfected adult shrimp were less likely to cannibalize juvenile shrimp than uninfected juveniles.
"The parasite is passed to its new host either when it dies and is eaten by another shrimp, or when one shrimp [cannibalizes] another. But we observed that uninfected shrimp avoid [parasitized] food and that is good for the shrimp as it means that they can obtain food through cannibalism but still avoid parasitic infection. Infected shrimp don't avoid infected juveniles. They consume infected and uninfected juveniles. This may be is because they are more hungry or because they are already infected so there is no incentive to avoid eating infected juveniles," Dunn said.
The Gammarus duebeni celticus is being gradually replaced by the invasive species Gammarus pulex in Irish waterways, and these findings suggest the parasite may be playing a role in weakling the native shrimp's resistance.
The findings were published in a recent edition of Royal Society Open Science.
