#mutalism

What’s interesting about this new digenean parasite is that the larvae cooperate using two different forms. The DNA confirmed that both the sailors and tiny passengers inside the hemisphere belong to the same species. These passengers, it seems, act as the infectious agents, waiting to infiltrate the gills or intestines of a fish that swallows them. The sailors, meanwhile, do the hard work of moving the blob through the water—but in sacrifice their own opportunities to reproduce. This phenomenon, in which one member of a species forgoes its own chance to reproduce so that another can, is called kin selection. And this, says Robert Poulin, a parasitologist at the University of Otago who was not involved, is “a really cool case of kin selection pushed to the extreme.” Scientists have studied the phenomenon in other kinds of trematode parasites while they are living inside their hosts. The “remarkable” new study shows that this division of labor happens in free-living larval forms as well, says Ryan Hechinger, a marine biologist at the Scripps Institution of Oceanography. “This finding highlights that trematodes are unique among all animal life.”