Variation that occurs within individuals, or subindividual variation, is one of the most important sources of phenotypic variation in plant populations. Individual plants produce a multiplicity of repeated structures, such as flowers, leaves, fruits or seeds, which are re-runs of the same genotype under different micro-environmental conditions. Trait differences among repeated organs cause intra-individual phenotypic variation. However, subindividual variation has been traditionally overlooked and treated as mere statistical noise. This is due to two fundamental problems, namely the misguided reasoning that subindividual variation is invisible to natural selection because it originates within one single genotype, and the unproven assumption that it lacks ecological relevance.However, what could be discovered when exploring this small-scale phenotypic diversity? Could it be relevant from ecological and evolutionary perspectives?
We measured, using HPLC techniques, the genome-wide cytosine methylation in basal leaves of inflorescences from Lavandula latifolia shrubs located at a Southern Iberia natural population.
Results/Conclusions
Individual plants were epigenetic mosaics, as revealed by internal heterogeneity in global DNA methylation of leaf nuclear genomes. Such maternal epigenetic mosaicism accounted for both within-generational (seed production, seed size) and transgenerational (seedling emergence, seedling size) fitness-related consequences of subindividual variation.
Our results highlight that subindividual epigenetic heterogeneity, as coarsely assessed by global DNA methylation levels possibly modified in response to patchy environmental conditions within a single individual, could have cascading ecological consequences of potential evolutionary significance. The fact that different modules of the same genetic individual can differ in their transgenerational fitness through molecular epigenetic mechanisms defies our understanding of evolutionarily relevant limits of biological organization in modular plants.