The genetic rules underlying the adaptive evolution of phenotypic robustness in experimental populations of Caernorhabditis elegans – ROBUSTELEGANS

Resilience to genetic or environmental insults results in phenotypic invariance among the individuals of a population, or “phenotypic robustness”. Yet, for evolution to occur there must be heritable phenotypic variation among individuals. Population genetic theory indicates that stabilizing selection may lead to the evolution of phenotypic robustness. However, it remains to be demonstrated that phenotypic robustness is adaptive and not a generic property of epistatic genetic architectures. Here, we propose to address this problem in a Caenorhabditis elegans experimental evolution model.

We have done an evolution experiment to high concentrations of NaCl in populations with standing genetic diversity and from which we derived a large number of inbred lines. Using this material, we will perform linkage association mapping for pairs of loci having epistatic effects on the the developmental processes that lead to variation in individual movement, across NaCl environments. For a subset of loci, we will replace all alleles into the genomic backgrounds of the ancestral population, using the recently developed CRISPR-Cas9 technology. With these experiments we will test whether the evolution of variation in epistatic gene interactions is adaptive, as we expect that in ancestral genomic backgrounds such epistatic interactions will be disrupted and lead to a decrease in the phenotypic robustness to changing NaCl concentrations. We will also test whether specific forms of epistasis are related to the evolution of phenotypic robustness.

The genetic rules underlying the evolution of phenotypic robustness must be common to all sexual organisms. Their finding will be a step forward in explaining the heredity of complex traits and the problem of "missing heritability" in humans, species of agricultural importance and other model organisms. The project is one of the few to use gene replacement in order to verify natural selection at the DNA sequence level and, to our knowledge, it will be one of the first addressing the evolutionary consequences of variation in epistatic effects.