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Abstract

The hermaphroditic nematode Pristionchus pacificus is a model system for comparative studies to Caenorhabditis elegans, with well-developed genetic, genomic, and transgenic tools. The availability of tools for functional investigations makes P. pacificus ideal for the genetic investigation of ecologically relevant traits. Under stress conditions P. pacificus forms resistant dauer larvae, a case of phenotypic plasticity in nematodes. A second type of phenotypic plasticity in P. pacificus is a dimorphism in its feeding structures, an evolutionary novelty of the family Diplogastridae. The mouth‑form dimorphism decision is made during larval development and is irreversible. The dimorphism consists of a stenostomatous (“St”) and a eurystomatous (“Eu”) form, which differ in the number and shape of teeth and by the width of the buccal cavity. Dauer larva formation and mouth‑form dimorphism share common environmental and molecular switches, suggesting partial co‑option of the dauer formation pathway in mouth‑form dimorphism evolution. Here we present a first approach to the identification of genes specific to the mouth‑form phenotype execution. Using a forward genetic approach, we identified eight mutant strains that are strongly biased to the Eu mouth form. Dauer formation in these mutants is normal, suggesting that the mutants are specific to the mouth-form dimorphism. Another screen for mutants that show a high frequency of St animals is currently ongoing. Mapping and cloning these mutants will provide unprecedented insight into the genetic mechanisms controlling of a polyphenic novelty.