Is parasitism of metazoa “a one-way ticket”?

Abstract

Various phenomena interpreted as possible cases of metazoans returning from obligate parasitism to the free-living state (a violation of the ecological interpretation of Dollo’s law) are critically considered. It is shown that among temporary and phase parasites, reversal to the free-living state is a very rare but not exceptional phenomenon. Such cases occur only among the temporary ectoparasites whose ancestors were predators. The only case of violation of Dollo’s law among permanent parasites, although an incompletely proved one, was detected in acariform mites of the family Pyroglyphidae (Acariformes: Psoroptoidea).