Abstract
The independent and repeated adaptation of populations to similar environments often results in the evolution of similar forms. This phenomenon creates a strong correlation between phenotype and environment and is referred to as ‘parallel evolution.’ However, there is ongoing debate as to when we should call a system either phenotypically or genotypically ‘parallel.’ Here, we suggest a novel and simple framework to quantify parallel evolution at the genotypic and phenotypic levels. We apply this framework to coastal ecotypes of an Australian wildflower, Senecio lautus. Our findings show that S. lautus populations inhabiting similar environments have evolved strikingly similar phenotypes. These phenotypes have arisen via mutational changes affecting common biological functions but occurring in different genes. Our work not only provides a common framework to study the repeated evolution of forms in nature, but also highlights S. lautus as an excellent system to study parallel evolution.
