Gammarus duebeni celticus, a species of shrimp native to Northern Ireland, has been found to display severe, cannibalistic tendencies when infected with the parasite Pleistophora mulleri.
After the parasite is introduced, it makes its home inside the shrimp's muscles (just one is about the size of a red blood cell), where it can easily multiply into the millions— causing the shrimp to become so ravenously hungry it will take the easiest route to obtain more food: namely, eating its own. Which feeds its parasitic companions in consequence.
Though the species is already known to eat its young in times of convenience (easy, right?), these instances were found to double in frequency with an excess of Pleistophora mulleri in the bloodstream.
In a press release, Dr. Alison Dunn, Reader in Evolutionary Biology at the University of Leeds' Faculty of Biological Sciences, ensured we understood an uninfected shrimp is normally transparent. "It takes over huge areas of the muscle, so instead of nice transparent shrimp you get a chalky appearance because of muscles packed with the parasite." She added, "Interestingly, our group also found previously that infected shrimp may be able to catch and eat less prey of other animal species. Perhaps cannibalism of smaller shrimp is the only way these sick animals can survive."
The paper is the first to suggest parasites are directly causal to cannibalism – but not the first work of fiction: the concept is noticeably similar to Scott Westerfield's 2005 novel, Peeps.
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