Transposable elements and an epigenetic basis for punctuated equilibria

Abstract

Evolution is frequently concentrated in bursts of rapid morphological change and speciation followed by longterm stasis. We propose that this pattern of punctuated equilibria results from an evolutionary tug-of-war between host genomes and transposable elements (TEs) mediated through the epigenome. According to this hypothesis, epigenetic regulatory mechanisms (RNA interference, DNA methylation and histone modifications) maintain stasis by suppressing TE mobilization. However, physiological stress, induced by climate change or invasion of new habitats, disrupts epigenetic regulation and unleashes TEs. With their capacity to drive non-adaptive host evolution, mobilized TEs can restructure the genome and displace populations from adaptive peaks, thus providing an escape from stasis and generating genetic innovations required for rapid diversification. This ''epi-transposon hypothesis'' can not only explain macroevolutionary tempo and mode, but may also resolve other long-standing controversies, such as Wright's shifting balance theory, Mayr's peripheral isolates model, and McClintock's view of genome restructuring as an adaptive response to challenge.

Transposable Elements, Epigenetics, and Genome Evolution

“…But by the end of the decade, he and his colleagues had concluded that because cytosine methylation is predominantly found in TEs, methylation was more likely to represent a nuclear defense system that had evolved precisely to "control" the destructive potential of "parasitic sequences," mostly transposons and retrotransposons (5,29). This view was widely accepted, and transposons are today almost universally referred to as "invaders," "parasites," or "parasitic sequences" (30)(31)(32)(33).…”

Reading TE leaves: New approaches to the identification of transposable element insertions

“…For example, in the Monodelphis research the investigators noted that much of the evolutionary innovation distinguishing metatherian from eutherian mammals was not due to differentiation in coding sequences but was instead due to differences in noncoding DNA and that TEs are a ''major creative force'' in mammalian evolution. Furthermore, one recent publication provided strong arguments suggesting that increases in transposable element activity in response to physiological stress may provide the foundation for the punctuated equilibrium model of evolutionary change (Zeh et al 2009). …”

Identification of Gene Related to Hard Bunch Phenotype in Oil Palm (Elaeis guineensis Jacq.)

“…One of these is Copia-like retrotransposon which is distributed over all oil palm genome (Castilho et al, 2000). Transposon could be activated by biotic and abiotic stress (Zeh et al, 2009). Present result indicated that the transposon was activated in oil palm genome due to dry periods exist during the year.…”