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Abstract:
There is more than meets the eye in the multilayered interactions among microorganisms, and deconstructing these intricate relationships in an ecological context has proved strenuous. The necromenic nematode Pristionchus pacificus is a genetic and evolutionary model used to elucidate the ubiquitous insect-nematode-bacteria complex. Global P. pacificus has a facultative affiliation with myriad scarab beetles and relies on the microbial blooms decomposing the beetle carcasses as a food source, and often must compete with other worms joining the feast. Consequently, as worm population densities increase, resources can become scarce, though P. pacificus can respond dynamically by utilizing two polyphenisms: dauer and mouth form. While the developmentally arrested dauer larva enables escape from harsh environmental conditions, P. pacificus can also develop a predatory mouth form that expands the worms’ dietary range to include other nematodes in addition to bacteria. We have, for the first time, explored population density and dispersal of P. pacificus by performing experiments in the wild on expansive temporal and spatial scales. Beetles were collected, decapitated, and placed in mesh-metal cages that allow for free movement of nematodes while enabling tracking of their dispersion. We found that there are two major dispersal events of dauers from the host carcass that reflect bacterial abundance, but not bacterial type. Intriguingly, all post-dauers worms on the carcass were predators, in contrast to both wild worms that did not develop via dauer and domesticated worms that did develop via dauer. In laboratory studies, we have traced this effect to be partially due to a stage-specific pheromone that induces the predatory mouth form in a density-dependent manner. Yet, this does not fully explain the patterns observed in nature, and ongoing analyses include single worm transcriptomics of wild dauers. We continue to investigate the intricacies of tripartite relationships, particularly the ecological forces influencing plastic phenotypes.
