Evolutionary loss of parasitism by nematodes? Discovery of a free-living filaroid nematode.
A cattle-drinking pool in nature reserve "Zwin" on the Belgian coast contained free-living third-stage infective filaroid juveniles. These juveniles clearly differ morphologically from all known nematodes. Morphological and molecular analyses indicate a position within the Filaroidea. The aberrant biology of this nematode, namely, a free-living stage in an aquatic environment, is unknown within this superfamily, and the evolution of the parasitic phenotype to a free-living state is generally thought to be unlikely. However, the obtained placement in the small subunit molecular phylogenetic tree suggests that this free-living stage is most likely a secondary adaptation. It is reasonable to assert that nematodes with complex life cycles still have the genetic potential for a reversion from parasitism to a (partial) free-living stage.
Bert
Wim
W
Department of Biology, Ghent University, Belgium. wim.bert@ugent.be
Messiaen
Marjolein
M
Manhout
Joeri
J
Houthoofd
Wouter
W
Borgonie
Gaëtan
G
D000818:Animals; D001530:Belgium; D005075:Biological Evolution; D005370:Filarioidea / Q000145:classification / Q000254:growth & development / Q000502:physiology*; D005618:Fresh Water / Q000469:parasitology*; D019015:Geologic Sediments / Q000469:parasitology; D008018:Life Cycle Stages / Q000502:physiology*; D010802:Phylogeny