This research will investigate the role of polyploidy in flowering plant diversification by studying pollinator preferences and reproductive interactions between plants differing in chromosome complement in the desert shrub creosote bush (Larrea tridentata). Determining the processes by which one species becomes two is crucial to understanding patterns of biodiversity and the functioning of ecosystems. Speciation, the process of new species formation, occurs when barriers to reproduction evolve between populations or groups. However, studying speciation for flowering plant species with multiple chromosome sets - a condition known as polyploidy - has proven difficult. Most flowering plants are polyploid, and groups with different chromosome numbers cannot easily interbreed, yet they are rarely recognized as different species. Reasons for this range from the physical similarity between plants with different chromosome numbers, to whether they have adapted to different environments. Although creosote bush with different chromosome complements inhabit ecologically distinct areas, they sometimes co-occur suggesting additional reproductive barriers are responsible for divergence. By combining DNA analyses, greenhouse experiments, and field investigations, this project will provide unprecedented insight into the early stages of speciation for groups of plants with different chromosome complements.
The overarching goal of this research is to bring polyploid species under the larger umbrella of speciation research by elucidating the biological significance of genome duplication to plant diversification. Polyploidy, especially autopolyploidy, where genome duplication occurs within a lineage rather than through hybridization, poses many challenges for evolutionary biologists, including understanding the relative importance of ecological and intrinsic genetic processes to diversification. Population-level analyses are critical for evaluating how plant-animal interactions and ecological adaptation influence divergence among "intraspecific" groups differing in chromosome complement, and whether diversification of polyploid species is similar to model diploid species. Moreover, this project, focused on the keystone plant species Larrea tridentata and its native pollinators in sensitive North American desert biomes, will help characterize the novel molecular diversity and ecological interactions comprising the cryptic biodiversity of polyploid species. The taxonomic recognition of populations differing in chromosome complement could significantly alter biodiversity estimates for certain parts of the world, especially temperate biomes, impacting our understanding of major ecological patterns.
