Low genetic diversity in populations of a clonal invasive plant limits sexual reproduction

Authors: PEARSE, IAN - Us Geological Survey (USGS); BECKER, ZOE - Colorado State University; ODE, PAUL - Colorado State University; Gaskin, John; West, Natalie

Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2025
Publication Date: 8/14/2025
Citation: Pearse, I., Becker, Z., Ode, P., Gaskin, J.F., West, N.M. 2025. Low genetic diversity in populations of a clonal invasive plant limits sexual reproduction. American Journal of Botany. Article e70083. https://doi.org/10.1002/ajb2.70083.
DOI: https://doi.org/10.1002/ajb2.70083

Interpretive Summary: Many invasive plants spread through a combination of clonal and sexual (via seeds) reproduction. However, in small populations, such as those common at the earliest stages of site invasions, clonality may interfere with reproduction via seed by limiting the availability of non-self partners for pollination. We examined associations between site genetic diversity(a proxy for the prevalence of clones in the population) and seed production in whitetop/hoary cress (Lepidium draba), a problematic weed in the western US. At a subset of sites, we then added on- and off-site-sourced pollen to plants (a pollen supplementation experiment) to test whether relatively lower seed production in low genetic diversity sites was associated with the availability of non-self pollen. We found that populations covering larger areas and nearer to rivers had relatively higher genetic diversity, and that higher genetic diversity was associated with higher seed production. At low genetic diversity sites, supplemental pollen from off-site, but not from on-site, did increase seed production. This result confirmed that pollen was limited by the pollen source. High diversity sites did not show the same pattern; those populations had no change in seed production with pollen supplementation regardless of pollen source. Our study shows that low-diversity sites are dominated by a few large clones, which reduces the seed production potential compared to high diversity sites. Management that targets seed production will therefore be particularly important in high diversity habitats, such as those associated with rivers, as these populations are more likely to be propagule sources for other less diverse populations.

Technical Abstract: Clonality, a form of asexual reproduction and spread, is common among invasive plants, though sexual reproduction via seeds is still important for the long-range dispersal of many of these plants. In small populations, clonality has been hypothesized to interfere with sexual reproduction by limiting outcrossing opportunities of a plant. We developed a structural equation model based on field surveys of the genetic diversity and seed production of Lepidum draba, a problematic invasive plant. Large sites and sites associated with rivers tend to have higher genetic diversity. Furthermore, percent seed fill as well as total seed production were considerably higher at sites with higher genetic diversity. The following year, we used six of the genotyped sites to test experimentally whether L. draba plants in low genetic diversity sites were limited by non-self pollen. At low genetic diversity sites, supplementation with pollen from outside of the site, but not from within the site, increased seed production. At high genetic diversity sites, pollen supplementation from off-site did not increase seed production. Our study shows that in low-diversity sites that are dominated by few large clones L. draba produces few seeds compared to high-diversity sites, and that this is likely due limited availability of non-self pollen. Because we found no shared genotypes of plants among even the closest populations of L. draba, it is likely that the vast majority of long-distance dispersal of this weed is due to seeds. Controlling high-diversity L. draba infestations that tend to be large and near rivers may be a way to reduce the seed-dependent spread of this invasive clonal plant.