Anthropogenic climate change will alter patterns of natural selection and pose strong evolutionary challenges to wild organisms. Plant species that have experienced genome doubling, or polyploidy, may have an advantage over those possessing a single copy of the genome because they can evolve faster or in novel directions in response to climate change. Examination of the creative role of polyploidy is important given that genome duplication is thought to have occurred in 47%-70 % of flowering plant species. This research will test the evolutionary potential of polyploids by imposing artificial selection for increased drought tolerance in a polyploid species (goldenrod, Solidago altissima) that varies naturally in chromosome number (2, 4, and 6 copies). The central hypothesis of this research will be supported if plants with higher chromosome numbers evolve faster in response to artificial selection.
This work will provide a large number of students with intensive hands-on training in lab and field techniques and provide opportunities for independent research at the graduate and undergraduate level. This research fulfills the objectives of the RUI program by addressing a question of great interest to society, the impact of climate change, and by providing solid training to a diversity of students who will become the next generation of scientists.
Numerous studies have shown that native plants are blooming eight days earlier or more in recent decades as climate changes. Yet we do not know if these phenological advances are a passive response to warmer environments (i.e. earlier spring germination and growth) or a genetic response to changes in natural selection (i.e. adaptive evolution). Furthermore, genetic attributes of plants may allow some populations to change faster than others. Many native plant species are polyploids meaning that in the past a macromutation doubled (or tripled, quadrupled etc.) the number of chromosomes sets per plant cell resulting, for example, in a species that includes both diploid individuals (2 sets of chromosomes) and tetraploid individuals (4 sets of chromosomes). It is often assumed that polyploids possess greater potential to evolve than their diploid progenitors because: 1) organisms with many gene copies harbor greater genetic diversity which is a requirement for evolutionary change, 2) genetic redundancy offers opportunities for duplicated genes to diverge and acquire new functions without compromising the original function, and 3) gene duplication increases the number of gene interactions, some combinations of which may enhance fitness. Thus, polyploidy may allow organisms to evolve faster or in novel directions compared to their diploid progenitors. Although this is a provocative idea and a compelling hypothesis, it had never been explicitly tested. An alternative hypothesis is that evolution of polyploids is slower because: 1) selection is less efficient at optimizing traits with more gene copies, 2) chromosome pairing is cumbersome causing genetic imbalances such as aneuploidy (chromosome loss) that reduce fitness, and 3) increased morphological and physiological plasticity of polyploids buffers populations against selection thereby reducing evolutionary response. This research has addressed this important gap in our understanding relating to the creative role of polyploidy in natural plant populations. This work is particularly important in light of the environmental challenges that populations face in the 21st century, such as climate change as well as other anthropogenic and natural environmental change. This research showed that polyploids represent a source of standing genetic variation in natural populations that is often be overlooked but is important because it can be mobilized by natural selection for adaptive evolution in different ways than consideration of diploids alone. Although several studies have shown greater molecular diversity in polyploids, this study brought unique data to bear on this issue by showing that polyploids also harbor greater quantitative genetic variation that is known to enhance evolutionary potential. Interestingly, polyploids were also more responsive to the environment (e.g. greater phenotypic plasticity) but there was little evidence that these responses were adaptive because they did not improve plant fitness. This work also showed that some polyploid lineages had higher competitive ability against a noxious invasive species. Collectively, these pieces of information increase our understanding of the nature of genetic variation in polyploid taxa and deepen our understanding of whether the genetic architecture of polyploids will enhance the persistence of populations in the face of climate change.
