Abstract
Animals and plants can predict decreasing food supplies by recognition of population density, and respond by adjusting behavioral and morphological traits. Population density in nematodes is detected through pheromones, influencing dormant (dauer) stage entry, and in some lineages alternative mouth-form decision (bacterivorous vs. predatory). Whether age is a relevant parameter in recognizing population density is not well understood. Here, we utilized the mouth-form plasticity of the model nematode Pristionchus pacificus and developmental pheromone profiling to study potential parent:progeny communication. Surprisingly, we observed adult-specific production of molecules that induce the predatory morph, even though adult mouth forms are no longer plastic. We introduce a novel dye-based method to differentiate populations in mixed-generation cultures, and found adults, but not peers, influence developing juvenile mouth forms. Finally, we applied a logistic growth model that demonstrates adults both lower the population carrying capacity and decrease the time until resource depletion. In the necromenic life cycle of P. pacificus, we view mouth-form plasticity as an alternative ‘Malthusian escape’ strategy to dauer that responds to age-specific population densities.