How did parasitic worms evolve?
Nematodes are important parasites of humans and other animals. Nematode parasitism is thought to have evolved by free-living, facultatively developing, arrested larvae becoming associated with animals, ultimately becoming parasites. The formation of free-living arrested larvae of the nematode Caenorhabditis elegans is controlled by the environment, and involves dafachronic acid (DA) and transforming growth factor (TGF)-beta signalling. Recent data have shown that DA acid signalling plays a conserved role in controlling larval development in both free-living and parasitic species. In contrast, TGF-beta signalling does not seem to be conserved; this difference perhaps points to how nematode parasitism did evolve.
Viney
Mark E
ME
School of Biological Sciences, University of Bristol, Bristol, UK.