The population genetics and evolutionary potential of diatoms

Since the Victorian era, people have remarked on the diversity and abundance of diatoms in marine waters. Diatoms are found across the sunlit ocean, are key components of marine food webs, and help to drive biogeochemical cycles. These characteristics are often used as measures of the ecological “success” of diatoms. In this chapter, we examine some of the evolutionary mechanisms that contribute to this success by reviewing the evolutionary strategies and rates that govern diatom population genetic structure and evolutionary potential. We highlight the field and lab data that have provided insights into contemporary evolution including standing genetic variation, natural selection, and rates of mutation, gene flow, recombination, and genetic drift. We also highlight the diversity of methodological approaches that have been used to examine genetic structure and contemporary evolution including single and several locus analyses, partial and whole genome sequencing efforts, experimental evolution, and modeling studies. This variety of approaches has revealed that diatom species are generally comprised of multiple genetically distinct populations. These populations are made up of genotypically diverse individuals with the ability to rapidly respond to their environment without any genetic change through acclimation. Populations also have the potential to respond to environmental change by shifting their genetic composition (evolution), due to their high genotypic diversity and ability to generate additional variation through mutation or heritable epigenetic responses. A key challenge for the future is to connect genotype with phenotype to better interrogate and understand how contemporary evolution functions in natural populations. This effort should include the development of culture-independent methods as well as robust support for laboratory assays to evaluate phenotypic variation across a diversity of traits and species. Finally, future efforts should be focused on obtaining a deeper understanding of how life history traits in diatoms, such as sexual reproduction and resting spore formation, influence their adaptive potential.