Parasitic Trematode flatworms form cooperative colonies in their molluscan hosts, with some individuals reproducing while others defend the colony. Although known to occur in a few groups — ants, for example — such complex social organization and altruistic behaviour is unusual.
Ryan Hechinger and his colleagues at the University of California, Santa Barbara, found two distinct forms of the flatworm. 'Soldiers' were around 2% of the body size of those that reproduced, precluding them from breeding but allowing them greater mobility to defend their colonies. Only the reproductive forms had embryos in their body cavities, whereas soldiers were more frequently observed attacking worms of other species or colonies (pictured).
The researchers say that the finding provides a new avenue by which to study the evolution of social behaviour.
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Zoology: Cooperative flatworms. Nature 467, 371 (2010). https://doi.org/10.1038/467371d
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DOI: https://doi.org/10.1038/467371d
