Clonal Evolution in the common monkeyflower (Mimulus guttatus)
Fundamental differences in the processes of plant development and reproduction compared to animals has implications of the processes of mutation accumulation and clonal evolution. In animals a germline is set aside early in development so any genetic modifications that occur during growth are not heritable. In plants the same set of cells that are responsible for vegetative growth also produce flowers and gametes. Many thousands of cell division occur during vegetative growth so plants have substantially greater potential for mutation accumulation than animals. In spite of this greater potential, mutation accumulation rates across generations are similar for plants and animals. Our goal is to resolve this paradox. We are using genomic approaches to evaluate the effects of cell lineage selection during stem growth on the process of clonal evolution and adaption in plants. This work is supplemented by analyses of the potential for gametophytic selection during pollen growth and selective ovule abortion after fertilization to filter deleterious mutations. This research has broader implications as clonal evolution occurs in a wide range of microbial species and is the fundamental cause of mammalian cancer.
Wind-dispersal in a logged Pinus ponderosa forest
A pillar of sustainable forestry is the maintenance of population genetic diversity. Populations with higher genetic diversity are more resilient to external stressors such as pests, temperature shifts, or drought. Because the act of logging removes genetic information from the population, genetic diversity is largely determined by dispersal, or the movement of pollen and seeds within and among tree patches. Although dispersal is recognized as a key ecological process in maintaining genetic diversity, the trajectories of pollen and seeds are notoriously difficult to track. In particular, wind-dispersed species—such as most coniferous trees—are subject to multiple factors at individual and population scales, from plant characteristics to patch structure. In clearcut forests, the sudden transition between forested and non-forested land introduces variations in wind speed and trajectory that may affect pollen and seeds carried on the wind. To capture this phenomenon, we use genetic parentage analyses to compare plant dispersal patterns in a continuous and clearcut forest. This research is done in collaboration with Dr. Raúl Bayoán Cal in the Mechanical and Materials Engineering department at Portland State University.
Landscape genetics of prairie species
Dispersal ranks as one of the most critical but least understood ecological processes. Direct measures of dispersal provide important information on local population dynamics, but are not useful for inferring extended time-scale processes such as range expansion. Indirect measures of dispersal using molecular genetic markers have been used to infer dispersal processes over larger scales, and when coupled with geographic information, "landscape genetic" models can provide information on landscape features affecting dispersal “resistance.” Understanding the potential for plants to disperse and colonize new sites is particularly critical as climate change affects the distribution of suitable habitat. We plan to estimate the dispersal potential and landscape resistance characteristics for a set of prairie species that differ in their associated pollen and seed dispersal vectors.
Invasion biology of slender false brome (Brachypodium sylvaticum)
False brome was first introduced into Oregon in the early part of the last century to test its potential for rangeland improvement, but B. sylvaticum has become an aggressive invader during the last 15 years. Accessions apparently crossed so the invasive plants now spreading across Oregon forests are recombinant products of hybridization. Introductions in Corvallis and Eugene retain unique marker signatures, but similar sets of native accessions contributed to the hybrid genotypes that are now spreading from each introduction location (Rosenthal et al. 2008). The false brome invasion is in early stages of range expansion and transition from a benign introduced species to an aggressive invader. Near introduction sites in Corvallis, many hectares of forest understory are dominated by monocultures of false brome that exclude native species and prevent the regeneration of canopy trees. Towards the leading edge of the expanding range in Oregon, populations are sparse and plant densities are low, with some notable exceptions.
A summary of our work is available here: Cruzan, M.B. 2019. How to Make a Weed–The Saga of the Slender False Brome Invasion in the North American West and Lessons for the Future. BioSceince 69:496-507. (https://doi.org/10.1093/biosci/biz051)
A summary of our work is available here: Cruzan, M.B. 2019. How to Make a Weed–The Saga of the Slender False Brome Invasion in the North American West and Lessons for the Future. BioSceince 69:496-507. (https://doi.org/10.1093/biosci/biz051)