The focus of ecological science is on the interactions of individual organisms with each other and their environments. The focus of evolutionary science is on the change in structure and function, from changes in genetics, of populations of individuals through time. From both perspectives, the degree to which the individual survives and reproduces (i.e. its fitness) is often fundamental to the research questions posed. But how do our perspectives and approaches change when the concepts of the “individual” and “fitness” are not easily defined? While these definitions are complicated by the life histories of many organisms (e.g. fungi, eusocial animals), they are for plants in at least two important but often overlooked ways: plants generate a substantial number of somatic mutations during their growth (gene sequence variation), and they often increase the number of genome copies in their cells relative to that which they inherited (genome copy number variation). In both cases, the resulting individual is actually a mosaic of genetic/genomic variation that contributes to phenotype and ultimately fitness. We have studied both of these phenomena to assess the degree to which they occur and their potential adaptive significance.
Results/Conclusions
Plants continuously produce stem cells at specific regions (e.g. the tips of roots and shoots), establishing an axis of development whereby cells divide and differentiate in columnar layers that generally do not intermix. Our sequencing of Populus trichocarpa has revealed that individuals harbored 4840 amino acid changes in 2569 genes on average across various assessed tissues. Mutations were overrepresented in defense metabolism and sexual reproduction genes. Mutations therefore occur much more commonly than expected, and selection on cell lineages promotes genetic variants of pathways that affect fitness. We have also assessed intra-individual variation within Arabidopsis thaliana. Individuals develop as mosaics of genome copy number (ploidy) which generally is 2–64 genome copies per cell depending on cell type. We have found that genotypes differ in their ploidy distribution, and so differ in the effectiveness of certain cell processes. Genotypes that regrow with the highest average ploidy following damage achieve the greatest fitness, but ploidy is reset each generation whereby enhanced ploidy contributes to fitness but cannot be inherited directly. Considering mutation and ploidy together, an adaptation of plants is their ability to develop as mosaics of genetic/genomic variation that contributes to plasticity in cellular phenotypes and ultimately to individual fitness.