Research in our lab is centered around the population and community ecology of weedy and invasive species. Within this broad field we currently have three main focus areas, which are described below.
1) What are the ecological implications of intraspecific diversity (genetic and/or phenotypic) for colonization success? (supported by the National Science Foundation: DEB-1433886)
Increasing propagule pressure (i.e., more seeds) is known to increase colonization success, but the largest pools of propagules should also contain the greatest genetic and phenotypic diversity. Propagule pressure may therefore affect colonization success in part because of the effects of genetic or phenotypic (trait) diversity within founding populations. To decouple these effects, we have used the weedy mustard Arabidopsis thaliana as a model invader in a field experiment near Houston, TX (on land owned by the Katy Prairie Conservancy). In addition to disentangling the effects of propagule pressure from those of population genetic diversity, this project was designed to assess relationships between genetic variation, trait variation and colonization success and to test hypotheses about how increased genetic diversity will affect recruitment curves (which show how colonization success responds to increasing seed input). Check out all the gory details here! Current and planned follow-up work is delving into the traits differentially expressed by these genotypes under varying environmental conditions, and how these differences in plasticity may influence colonization success.
Despite many compelling reasons to use A. thaliana for studying diversity effects on colonization and invasion, we’ve also begun addressing these questions in non-model systems where these basic concepts may have important real-world applications. For example, giant ragweed (Ambrosia trifida) is a serious agricultural and allergenic weed that has increased in geographic range and pest status within North America (where it is native). Giant ragweed populations are extremely variable morphologically, so we can hypothesize that its spread may have been aided through the increase of genetic and/or phenotypic variation in newly colonized populations. Together with colleagues in the Horticulture and Crop Science Department here at OSU, plus a crew of awesome OSU undergraduates, we’ve quantified how giant ragweed partitions morphological variation within and among populations across the Midwest. See our recent paper in Evolutionary Applications for more info on this!
One particular dimension of trait variation that should influence colonization and early establishment relates to plant breeding systems. PI Hovick has had an ongoing collaboration with an international group of researchers as part of a NESCent working group organized to test the predictions of Baker’s Rule. Baker’s Rule states that species and populations colonizing islands should have an enhanced degree of uniparental reproduction (e.g., self-compatibility or vegetative reproduction). We might analogously expect that introduced species will be more self-compatible or capable of clonal reproduction than native species, or that the introduction/invasion process might select for self-compatibility (either among or within species).
2) How does interspecific hybridization and/or polyploidy influence invasiveness and colonization success in plants?
Hybrids may be better able to establish and spread into new regions than their parental taxa if they contain more variation or novel combinations of genes relative to their parental taxa. This hypothesis is widely cited but remains poorly tested, although data from our recent meta-analysis is consistent with this hybridization-invasion hypothesis. Some of our experimental work has also indicated that hybridization in radish (Raphanus sp.) enhances invasiveness in a novel region and that the critical traits leading to fitness gains in hybrids may differ among regions. Thus, not only can hybridization promote invasiveness, but it can apparently do so via an even greater diversity of pathways than previously imagined.
Led by PhD candidate Kali Mattingly, we are currently investigating whether hybridization plays a role in the invasive wetland species purple loosestrife (Lythrum salicaria). The closely related wand loosestrife (Lythrum virgatum) is available for sale in many places as a landscaping alternative to purple loosestrife, which could impact the phenotypes expressed by loosestrife in the field and even influence its adaptive potential over longer time scales. Kali has documented morphometric patterns from herbarium specimens that are consistent with an increased incidence of hybridization between these species over time since wand loosestrife became available for sale. We are now processing field-collected leaf samples to determine whether a genetic signature of wand loosestrife is detectable in wild purple loosestrife populations, using species-specific genetic markers Kali has developed. Stay tuned for updates!
3) How does human land-use and its associated stressors influence invasibility of wetlands and key characteristics of wetland plant species?
A more recent emphasis in our lab has been to investigate the effects of anthropogenic land-use on naturally-occurring plant communities (led so far by MS students Christian King and Danie Frevola). We use wetlands as a model system for this work in part because they often act as sinks in the landscape for contaminants, nutrients and propagules. We have identified various components of wetland soils (resources as well as contaminants) that vary consistently from urban to rural sites and that appear to influence plant community composition and structure (King and Hovick, ms in prep). But the temporal delivery pattern of these soil components itself (e.g., as discrete resource pulses versus more homogenous delivery over time) may also affect plant populations and communities, as well as ecosystem services such as invasion resistance. A common garden experiment we conducted with two closely related wetland grasses (invasive Phragmites and its native conspecific) suggests that phenotypic and performance responses to nutrient pulses may be similar, at least for these taxa, and that (unexpectedly) nutrient pulses may have detrimental effects on plant performance (Frevola and Hovick, in press).