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EvoDevo  2012 

Developmental plasticity and the evolution of parasitism in an unusual nematode, Parastrongyloides trichosuri

DOI: 10.1186/2041-9139-3-1

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Abstract:

We investigated the role of dauer development in the nematode, Parastrongyloides trichosuri, which has retained a complete free-living life cycle in addition to a life cycle as a mammalian gastrointestinal parasite. We show that the developmental switch between these life histories is sensitive to the same environmental cues as dauer arrest in free-living nematodes, including sensitivity to a chemical cue produced by the free-living stages. Furthermore, we show that genetic variation for the sensitivity of the cue(s) exists in natural populations of P. trichosuri, such that we derived inbred lines that were largely insensitive to the cue and other lines that were supersensitive to the cue.For this parasitic clade, and perhaps more widely in the phylum, the evolution of parasitism co-opted the dauer switch of a free-living ancestor. This lends direct support to the hypothesis that the switch to developmental arrest in the dauer larva acted as a pre-adaptation for the evolution of parasitism, and suggests that the sensory transduction machinery downstream of the cue may have been similarly co-opted and modified.One of the hallmarks of the phylum Nematoda is the repeated evolution of parasitism. This important life history strategy has arisen at least nine times in the phylum, based on molecular phylogenies [1-3], to give rise to at least six groups of animal parasites and three groups of plant parasites, each of which are interspersed with non-parasitic relatives. It would appear unlikely that one mechanism of evolution resulted in these multiple events. Our focus has been on the evolution of parasitism in terrestrial nematodes that have a developmentally arrested dauer stage, which evolved in the ancestral mono-phylum Secernentea [4].These nematodes' life cycles are somewhat diverse, but are all essentially variations on a conserved life cycle composed of four larval stages punctuated by molts and culminating in a reproductive adult. Although nematode parasites have

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