Pleiotropy

The small subset of mutations that are beneficial in any given environment are the underappreciated gems of the mutational spectrum. This should be surprising given their importance to countless biological processes but likely results from problems of detection. The fine scale benefits they provide an organism are usually much less dramatic than when the entire function of a gene is lost, which is why beneficial mutations are understudied. Even less understood is the extent to which these mutations affect fitness in other environments, or their pleiotropic effects. The relationship between beneficial mutations and their pleiotropic effects has begun to be examined (2, 5, 10, 11), but a better understanding of the abundance and distribution of pleiotropic effects is needed, especially because antagonistic pleiotropy is what dictates niche breadth. (1). For example, it is unclear if the first steps of adaptation to one environment affect fitness only in that environment or if these first steps affect fitness in a range of environments, potentially resulting in trade-offs and a narrower niche. This specialization to a single environment can also reduce the fraction of mutations that can produce beneficial alleles (12), meaning that well-adapted organisms can acquire fewer beneficial mutations than less well-adapted organisms.