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Abstract

Pristionchus pacificus shares with Caenorhabditis elegans many technical features and has been developed as a model system in evolutionary developmental biology. We have started a genetic and molecular analysis of dauer formation in P. pacificus. The dauer stage is important in the ecology of many nematodes and evolutionary alterations of dauer formation should play crucial roles in the adaptive radiation of nematodes. P. pacificus dauers have several features not common to C. elegans, such as prominent amphids, lack of alae, and the secretion of an oily substance on the body surface. The control of dauer entry and exit is of utmost ecological importance because erroneous decisions lead to either less progeny or survival. Therefore, this control might be subject to substantial evolutionary modifications. To reveal if there are differences in dauer formation between P. pacificus and C. elegans, we tested if P. pacificus dauer formation is controlled by a pheromone. Extracts prepared from supernatants of P. pacificus liquid culture strongly induced dauer in P. pacificus. By contrast, C. elegans pheromone did not induce dauer formation in P. pacificus. To identify the genes underlying the P. pacificus dauer formation, we screened for dauer formation abnormal mutants. We obtained more than 10 strains of dauer formation defective (daf-d) and dauer formation constitutive (daf-c) mutants. By mapping and cloning we identified mutations in Ppa-daf-12 in some of the daf-d mutants, suggesting evolutionary conservation of the involvement of the nuclear hormone receptor in dauer formation. Furthermore, we found that dafachronic acid, a steroidal ligand for Cel-DAF-12, serves as ligand for Ppa-DAF-12. Thus, we identified the dafachronic acids-DAF-12 system as an evolutionarily conserved mechanism for dauer formation.