Environmental change and the evolution of genomes: Transposable elements (TEs) as translators of phenotypic plasticity into genotypic variability

1. Phenotypic plasticity is generally explained as the result of epigenetic mechanisms modifying gene expression in response to changing environmental conditions. However, the biology of transposable elements (TEs) suggests that such elements may also induce differential gene expression by affecting regulatory regions. 2. We discuss the ecological and evolutionary relevance of epigenetic modifications versus transposon activity, taking into account that epigenetic modifications are generally reversible but that the modifications induced by TEs are stably inherited. 3. We outline our perspective on the multiple roles played by environmental changes in the context of adaptive evolution. Environmental perturbations can induce phenotypic variations via epigenetic modulation of gene expression and promote, at the same time, genetic variability by triggering bursts of TE activity; finally, they select which genetic variations are most advantageous for survival. 4. Within this context, the production of environmentally induced advantageous phenotypes by epigenetic mechanisms could represent an immediate process of adaptation followed by TE-induced genotypic changes that make these phenotypic variants heritable through the germ line. This scenario could lead TEs to play different roles in the function of the time-scale of ecological variation, such as those related to climatic change in the current context of global change. 5. In conclusion, we propose that through TE activation, environmental changes can act as inducers of genetic variability, upon which they also act as selective forces, thus triggering rapid evolutionary processes.