Epigenetic ecotypes in animals: persistent environmental adaptation in the absence of genetic variation

Abstract

According to prevailing theory, sexually reproducing animals adapt to different environments by the production of phenotypic variation from the standing genetic variation and selection of the most suited phenotypes. Contrary to all expectations, asexually reproducing animals can also inhabit broad ranges of geographical latitudes, altitudes and habitats, despite virtual genetic identity. Recent whole genome analyses of differently adapted clonal populations and genetically impoverished invaders revealed that they can use epigenetic variation instead of genetic variation to stably adapt to different environments. The required phenotypes are produced from the same DNA sequence via changes in gene expression, which is trigged by strong environmental cues and mediated by environment-sensitive epigenetic mechanisms like DNA methylation. Habitat-specific epigenetic fingerprints were maintained over subsequent years, pointing at the existence of epigenetic ecotypes. Obviously, all animals can produce different phenotypes from the same DNA sequence, but in asexually reproducing populations, genetically impoverished invaders, sessile taxa and species with long generation times it is apparently of prime importance. In contrast to beneficial genetic mutations and meiotic gene combinations that require many generations to be established in a population, environmentally-induced epigenetic changes and subsequent alterations in gene and phenotype expression affect population members synchronously in the first exposed generation, providing an ideal means for fast, directional adaptation to changing conditions. The production of different phenotypes from the same genome in response to different environmental cues via epigenetic mechanisms is also suitable to explain the “general-purpose genotype” and the “genetic paradox of invasion”.