Summary
Many animal and plant species respond to high or low population densities by phenotypic plasticity. To investigate if specific age classes and/or cross-generational signaling affect(s) phenotypic plasticity, we developed a dye-based method to differentiate co-occurring nematode age classes. We applied this method to Pristionchus pacificus, which develops a predatory mouth form to exploit alternative resources and kill competitors in response to high population densities. Remarkably, only adult, but not juvenile, crowding induces the predatory morph in other juveniles. Profiling of secreted metabolites throughout development with HPLC-MS combined with genetic mutants traced this result to the production of adult-specific pheromones. Specifically, the P. pacificus-specific di-ascaroside#1 that induces the predatory morph exhibits a binary induction in adults, even though mouth form is no longer plastic in adults. This cross-generational signaling between adults and juveniles may serve as an indication of rapidly increasing population size. Thus, phenotypic plasticity depends on critical age classes.
