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Schlagwörter:
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Zusammenfassung:
Phenotypic plasticity is the ability of organisms with the same genetic complements to develop different phenotypes in response to environmental influences. This phenomenon is extremely widespread, but evolutionary consequences of phenotypic change in the absence of genetic change are currently unclear. Numerous ideas have been developed to explain the potential significance of phenotypic plasticity for evolution, but the formulation of explicit falsifiable hypotheses requires better mechanistic insight into plastic development. An ideal study system to investigate phenotypic plasticity must combine amenability to experimental genetic research and accessibility of lineages in which one of the alternative phenotypes has been fixed. Plasticity in feeding structures of diplogastrid nematodes satisfies both of these criteria. Isogenic lab populations of the species Pristionchus pacificus can develop two discrete alternative phenotypes depending on the rearing conditions. The eurystomatous (Eu) morph has a wide mouth with two hooked teeth and is a facultative predator. The stenostomatous (St) morph has a tube-like mouth with only one tooth and is a non-aggressive microbial grazer. Previous research uncovered the role of pheromones and identified the sulftase EUD-1, the sulfotransferase SULT-1 and the nuclear hormone receptor NHR-40 as regulators of mouth form decision in P. pacificus. In my thesis work, I aimed to reveal further environmental factors and genetic players controlling the phenotype. I discovered the effect of food composition and helped identify the effect of a range of solid and liquid media on the ratio between morphs in the population. On the genetic side, I found that eud-1 is part of a chromosomal cluster of functionally related genes, reminiscent of supergenes. Further, I isolated another transcription factor regulating morph decision, NHR-1, and identified a set of common transcriptional targets between NHR-40 and NHR-1, which may be the genes directly involved in making the alternative phenotypes. In addition, I elucidated the role of heat shock proteins in canalizing the development of discrete alternative morphologies. Finally, I participated in studies that provide a genome-wide description of chromatin states in P. pacificus and implicate histone acetylation in specifying the Eu morph.
