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Flatworm caste

Source: TW

Caste in flatworms

People are familiar with the multiple origins of castes among eusocial insects that parallel the IE caste system in humans (The puruSha as a superorganism). But recent findings have unexpectedly revealed a caste system in parasitic flatworms the digenean trematodes, that infect humans and other vertebrates. Digenean parasitic flatworms cycle between infecting a vertebrate final host and two intermediate hosts (see figure 1 for life cycle), where the 1st is usually a snail where the founder establishes a colony by cloning itself. They block the snail’s reproduction but make it produce a thicker shell and have a larger mass, thus making it a fortress for themselves. To protect the fortress from invasion by other worms, the clonal colony of worms differentiates into a reproductive caste and a soldier caste that kills the invaders. A recent study has shown that such caste differentiation occurs in Haplorchis pumilio, a human parasitic worm that produces clearly differentiated non-reproductive soldiers with killing mouthparts (Figure 2). They were seen killing much larger competitor worms of the genus Philophthalmus (Figure 3). However, the soldiers do not target worms of the self species. In general terms, the flatworm soldier caste guarding their hijacked snail is reminiscent of snapping shrimps guarding their residence sponge and the soldier caste of aphids, gall thrips and clonal wasps defending their hosts. This adds to the general of caste formation in animal evolution.

https://pnas.org/doi/10.1073/pnas.2400953121
https://royalsocietypublishing.org/doi/10.1098/rspb.2010.1753