CAREER: Discovery of the molecular mechanisms underlying microevolution of phenotypic plasticity in a developmental trait

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When organisms are exposed to environmental differences, like changes in temperature conditions, they can grow into alternative forms that are more adapted to particular environments. This project investigates how a nematode roundworm makes the decision to become a long-lived and stress-resistant form instead of a proliferative form that is stress-sensitive. Currently there is little understanding how these types of decisions are made at the molecular level. High-throughput measurements, genome sequencing, and genetic methods will be used to examine this mystery and lay the groundwork for future projects examining how animal development changes in responses to divergent environmental cues. Undergraduate and high school student training is an important component of this grant. High school teachers will develop classroom activities for STEM students in cooperation with the principal investigator and high school students will visit the laboratory to carry out hands on experiments with the worms.Phenotypic plasticity, or the expression of different phenotypes by the same genotype, drives evolutionary adaptation to shifting environments. Despite numerous well-known examples, little is known about the genetic underpinnings and molecular mechanisms that generate phenotypic plasticity. The goal of this grant is to discover how microevolution of this plasticity occurs using the tractable metazoan system Caenorhabditis elegans. Depending on environmental conditions, these nematodes enter an alternative developmental fate, called dauer, or continue development to reproductive adults. Early larval-stage animals that sense high temperature, low food availability, and high population density initiate the development of the dauer stage. Once conditions improve, dauers re-enter development to become reproductive adults. Much of what is known about dauer comes from the study of a single laboratory strain. Although natural variation in dauer formation has been observed, the molecular mechanisms that lead to phenotypic differences remain unknown. An unbiased approach is needed to discover the genes that underlie natural variation in dauer formation in order to understand how phenotypic plasticity evolves. Species-wide association mapping will be performed using a novel high-throughput assay in order to identify loci that underlie differences in this developmental trait. These loci will be narrowed to candidate genes using well tested experimental and computational techniques and then variants will be validated using genome editing. These approaches will lead to discovery of the number and the sizes of genetic effects, the signatures of selection that occur at those loci, and then define the parts of the dauer network involved in the microevolution of phenotypic plasticity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.