Selection-driven trait loss in independently evolved cavefish populations

Laboratory studies have demonstrated that a single phenotype can be
produced by many different genotypes; however, in natural systems, it is
frequently found that phenotypic convergence is due to parallel genetic
changes. This suggests a substantial role for constraint and determinism
in evolution and indicates that certain mutations are more likely to
contribute to phenotypic evolution. Here we use whole-genome resequencing
in the Mexican tetra, Astyanax mexicanus, to investigate how selection has
shaped the repeated evolution of both trait loss and enhancement across
independent cavefish lineages. We show that selection on standing genetic
variation and de novo mutations both contribute substantially to repeated
adaptation. Our findings provide empirical support for the hypothesis that
genes with larger mutational targets are more likely to be the substrate
of repeated evolution and indicate that features of the cave environment
may impact the rate at which mutations occur.