José Cerca

Parallel and convergent evolution are textbook examples of the role of natural selection in evolution. However, these terms are used interchangeably, and sometimes with conflicting meanings. This has resulted in confusion, which hampers the understanding of the processes underlying these important forms of evolution. In this synthesis, I discuss the issues with current definitions of parallel, repeated and convergent evolution, and provide a framework aimed at solving these issues. This framework makes an important distinction between environmental properties and organismal properties, with the first involving the role of similar and non-similar environmental and selective pressures. The organismal properties include the genomic-basis where the process (mutation, standing genetic variation and gene flow) and the location (homologous nucleotide, homologous gene region or non-homologous gene region) are emphasised, and the phenotype (convergent or parallel evolved). I restrict the use of the terms parallel (evolution of similar and derived phenotypes, from similar ancestral phenotypes) and convergent (evolution of similar and derived phenotypes, from dissimilar ancestral phenotypes) evolution to the phenotypic level, thereby restoring its original meaning before the genomic revolution. I argue that this framework and nomenclature provide a clear resolution to study parallel and convergent phenotypic evolution across fields while maintaining the interest in its genomic and ecological grounds. Crucially, this framework stresses the importance of a multidisciplinary focus, integrating ecology, genomics, and phenotypes to determine whether parallel or convergent phenotypic evolution has taken place.