Microevolution of molecular mechanisms for developmental plasticity in Pristionchus nematodes

Genes alone do not determine traits, and a widespread phenomenon in animals and plants is for traits to develop differently in response to varying pressures from the environment. This phenomenon is known as “developmental plasticity,” which in some extreme cases acts as a “switch” between alternative and often strikingly different forms. In some examples, such switches have been defined in terms of individual genes and the products they encode.

However, a persistent challenge has been to understand how these switches, specifically the molecular processes responsible, evolve in nature. The goal of this research is to identify, using species of nematodes that assume different feeding-forms in response to starvation and local competition, the genetic basis for how developmental plasticity evolves.

Moreover, by drawing on multiple, complementary types of variation in plasticity among populations, the project will determine which features, if any, are generalizable across them. The project will train undergraduate, graduate, and postdoctoral students in research that integrates genetics, developmental biology, and evolution. The research will also support two science-outreach programs at Indiana University: (i) the investigating laboratory will host and mentor underrepresented minority high-school students in their own research projects in an annual summer program, and (ii) the principal investigator will guide Indiana high-school teachers in developing projects, experiments, and activities to be implemented in the classroom to improve the teaching and learning of state life-science standards.

This research will advance a functional-genetic understanding of the evolution of polyphenism, or discrete developmental plasticity. Using a model system for developmental genetics, Pristionchus nematodes, this research will link defined molecular mechanisms of a morphological polyphenism to the allelic variants that explain natural variation in that polyphenism.

First, the research will determine the quantitative genetic basis for observed divergence of plastic responses between wild isolates of the species Pristionchus pacificus. This aim will be met by mapping, validating, and functionally characterizing allelic variants causing differences in a threshold response to the environment. Second, the research will determine the quantitative genetic basis for hidden divergence of polyphenism regulation between wild isolates with similar plastic responses.

This aim will be met by revealing how combinations of variants, which can be uncovered through transgressive phenotypes, are responsible for polyphenism evolution. Third, the research will experimentally determine the repeatability of proximal mechanisms for plasticity evolution. This aim will be met by replicating scenarios of experimental evolution of Pristionchus populations in response to a polyphenism-influencing environment.

By integrating a model for polyphenism genetics into a microevolutionary framework, the research will describe: (i) the molecular capacity of polyphenism’s regulatory mechanisms to change; (ii) how generalizable the types of changes are across parallel cases of divergence; (iii) the impact of diverging plasticity modifiers on the polyphenism developmental network, including those components that effect the ultimate forms produced.

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.