Cruzan Lab - Portland State University - Biology

Research Projects

Landscape genetics of prairie species - responses to climate change

SidalceaDispersal 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. 

Clonal Evolution in the common monkeyflower (Mimulus guttatus)

Mimulus guttatusFundamental 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. With each mitotic cell division during stem growth there is potential for mutation. 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.

Invasion biology of slender false brome (Brachypodium sylvaticum)

false bromeFalse 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.

Adaptation during invasion - After extra-range dispersal individuals are likely to encounter novel environmental conditions. Oregon has a contrasting climate relative to the source regions in Western Europe.  We are investigating phenotypic, transcriptomic, and genomic variation in native and invasive populations of false brome.  This effort is facilitated by the availability of genomic resources in the closely-related species, B. distachyon.

Evolution during range expansion - Plants towards the edge of the expanding range often display increased vigor in spite of the low genetic variation.  We are testing the hypothesis that range expansion reduces inbreeding depression to produce more vigorous invaders.

Influence of soil fungal mutualisms on invasion success - Introduced plants are exposed to novel soil fungal communities that may facilitate or impede their success.  Arbuscular mycorrhizal fungi (AMF) are obligate mutualists that must associate with plant roots to successfully reproduce. Networks of mycelia may connect multiple plants - including native and invasive competitors. We are examining the ecological and evolutionary aspects of AMF associations on the success of the invasive false brome.

Hybridization and adaptation in Piriqueta

PiriquetaHybrid derivatives of introgression between two morphotypes of Piriqueta in central Florida have spread to displace their parental progenitors.  Adaptation in these derived hybrids include adaptive plasticity responses to drought for leaf morphological characters.  These population have also undergone adaptive evolution of floral morphology that was facilitated by genetic variation introduced via hybridization.  Ongoing studies of these plants include temporal plasticity responses to drought for phenotypic and transcriptomic traits.