The genetic and molecular mechanisms of environmental perception during mouth-form plasticity regulation in the nematode Pristionchus pacificus

Polyphenism, a discrete case of phenotypic plasticity, is widely present in nature. Nevertheless, the genetic mechanisms regulating polyphenisms are not well understood, as genetic and molecular tools are limited in many of these organisms. One of the most well-studied developmental switch networks regulating a polyphenism in animals is the stomatal dimorphism in the hermaphroditic nematode Pristionchus pacificus, which is responsible for the formation of either a predatory or bacterivorous morph. A switch network involving the eud-1/sulfatase has been identified and characterized in great detail. However, the upstream pathways that perceive environmental information into the switch network are currently not known. Temperature is a general developmental cue for phenotypic plasticity. Therefore, we >are investigating the role of temperature cues in the mouth-form decision in P. pacificus. Phenotyping mouth-form ratios in 10 wild isolates on temperatures between 12° and 28°C revealed a conserved concave reaction norm, but also substantial natural variation. We conducted a forward mutagenesis screen using the strain RSA635 at 27° C and isolated 12 mutants, which were defective for the high temperature response. Identification of the genetic lesion in one of these mutants revealed the P. pacificus daf-11/guanylate cyclase. In C. elegans, daf-11 is expressed in the nervous system and is inhibiting high temperature mediated induction of dauer larvae, another polyphenic trait. However, we do not observe constitutive dauer larvae in Ppa-daf-11 mutants on high temperatures. Therefore, our results show co-option of the high-temperature dauer forming pathway into mouth-form plasticity, and suggest developmental drift of the high-temperature dauer induction between these two related nematodes. We will describe our ongoing studies to identify the molecular mechanisms of temperature perception during mouth-form plasticity in P. pacificus