Platyhelminthe worms capable of producing sterile soldiers that defend their colony

Platyhelminthe worms, a freshwater parasitic species known to infect humans, have been found to establish communities in which some members are created with special characteristics to act as soldiers, similar to what happens in communities of ants or termites, for example.

The discovery was made in a study led by Ryan F. Hechinger, of the Scripps Institution of Oceanography, part of the University of California in San Diego, and Daniel Metz, of the same institution and now at the University of Nebraska-Lincoln, in the United States.

The discovery elevates this species of parasitic flatworm to the rank of animals capable of establishing complex societies, such as ants, bees and termites, which also have distinct classes of workers and soldiers who have given up reproduction to serve their colony.

When introduced into humans, usually through the consumption of raw or undercooked fish, this species of flatworm, Haplorchis pumilio, can cause gastrointestinal problems and, in severe cases, stroke or heart attack.

Unlike bees and termites, colonies of this platyhelminthe species do not live underground or in a tree hole, but inside the body of a living aquatic snail. The parasites do not kill the snail, but instead drain it of nutrients over a long period of time, while producing free-swimming clones in search of fish, the platyhelminthes’ next host in their complex life cycle.

Although some other species in this class of parasitic platyhelminthes, the trematodes, also have soldiers, the soldiers of these species may still contain some dormant reproductive tissue, suggesting that they may eventually produce offspring. This study is the first evidence that there are trematode soldiers so physically specialized for their task that they lack reproductive tissues and appear permanently unable to reproduce.

Typically, Haplorchis pumilio form colonies inside freshwater snails of the species Melanoides tuberculata and then infect two other hosts in succession during their life cycle: usually fish and, finally, a warm-blooded vertebrate. Both the trematode and the snail are native to Africa and southern Asia, but are invasive species in other parts of the world, for example in the Americas.

The researchers found the soldier caste during the life cycle phase of this trematode in which it forms a colony inside the snail. The soldiers defend the colony from intruders (such as other parasites) by means of a large mouth that generates a powerful suction capable of piercing its enemies and sucking out their entrails.

The parasitic platyhelminthe Haplorchis pumilio produces non-reproductive soldiers (left image) that have much larger mouths than their reproductive colonymates (center image). The soldiers use their mouths to defend the colony by producing powerful suction blasts to kill their enemies (right image). (Photos: Dan Metz)

The study is titled “The physical soldier caste of an invasive, human-infecting flatworm is morphologically extreme and obligately sterile.” It has been published in the academic journal Proceedings of the National Academy of Sciences (PNAS). (Source: NCYT by Amazings)