New insights into molecular evolution: prospects from the Barcode of Life Initiative (BOLI).

Geographic and temporal patterns of morphological and behavioral diversifications among species stimulated Darwin to propose a mechanism for evolutionary change through natural selection. Scientific developments have revealed an even more fundamental level of biological complexity: sequence variation in DNA. While genome projects yield spectacular insights into molecular evolution, they have targeted only a few species. In contrast, the Barcode of Life Initiative (BOLI) proposes a horizontal approach to genomics, examining short, standardized genome segments across the sweep of eukaryotic life, all 10 million species. BOLI will extend our understanding of evolution and speciation in varied ways. It will facilitate quantification of biological diversity by disclosing cryptic species and enabling a rapid survey of taxon diversity in groups that have hitherto received scant morphological examination. It will facilitate assignment of life history stages to known species and provide a first estimate of species ages. It will also reveal key features of the mitochondrial genome, because the evolutionary properties of barcodes relate to those in the mitochondrial genome as a whole, acting to flag taxonomic groups or species with unusual nucleotide composition or evolutionary rates. The growing volume of barcode records has revealed that sequence variability within species is generally much lower than divergence among species (barcoding gap), a pattern that occurs in diverse lineages, suggesting a pervasive evolutionary process. Low variability may reflect recurrent selective sweeps of favored mitochondrial variants propagating as single linkage units across species. If this hypothesis is substantiated, the implications are significant, particularly for our understanding of molecular evolution of mitochondrial DNA and its relationship with species delineation.