Fig. 1
Developmental regulation of polyphenism in Pristionchus pacificus. a Alternative morphs (eurystomatous, “Eu,” and stenostomatous, “St”) have mouthparts that allow different ecological roles: the Eu morph differs in the shape of its dorsal tooth (false-coloured blue) and the presence of an additional, opposing tooth (yellow), which enable predatory feeding on other nematodes. b Known genetic factors regulating the mouth-form polyphenism (left) and their known or presumed spatial context in the developing larva (right). Sensitivity to environmental cues (green) of nutritional stress and crowding (pheromones dasc#1 and ascr#1) occurs during postembryonic development, where “starvation” (experimental withholding of food) has an influence as early as the first post-hatch (J2) stage10 and the presence of other nematodes as late as the J3 and possibly J4 (pre-adult) stage11. Downstream of these cues, which in C. elegans are primarily intercepted and interpreted by several amphid neurons55, 56, parallel regulatory elements including endocrine (dafachronic acid) signalling, chromatin modification (by LSY-12 and MBD-2), and eud-1 asRNAs converge on a polyphenism “switch.” This switch includes EUD-1 and NHR-40, which together comprise a signalling system that originates in the central nervous system (red) and ultimately decides between alternative feeding morphologies (purple). The decision is irreversible by the J4-adult moult, resulting in adult phenotypes best matched to the environment experienced as larvae
