High genetic diversity in the landscape suggests frequent seedling recruitment by Euphorbia virgata Waldst. & Kit. (leafy spurge) in the northern U.S

Authors: West, Natalie; GASKIN, JOHN; MILAN, JOSEPH - BUREAU OF LAND MANAGEMENT; Rand, Tatyana

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2022
Publication Date: 12/19/2022
Citation: West, N.M., Gaskin, J.F., Milan, J., Rand, T.A. 2022. High genetic diversity in the landscape suggests frequent seedling recruitment by Euphorbia virgata Waldst. & Kit. (leafy spurge) in the northern U.S. Biological Invasions. 25:645-652. https://doi.org/10.1007/s10530-022-02954-9.
DOI: https://doi.org/10.1007/s10530-022-02954-9

Interpretive Summary: When weeds can reproduce both through seed and clonal, weed density and turnover can drive and be driven by the relative success of these co-occurring strategies. Such considerations are particularly important for sustained management with biological control (biocontrol), which relies on specialized insects with selective feeding patterns to limit weed populations. We quantified genetic diversity, weed density, and associated biocontrol agent (Aphthona species complex) abundance in 100 leafy spurge (Euphorbia virgata Waldst. & Kit.) populations across three US states. This survey was intended to provide insight into: 1) how often seedlings contribute to population growth, which is strongly related to genetic diversity in clonal plants such as leafy spurge; and 2) the degree to which leafy spurge density is related to the balance of vegetative and seedling recruitment within local populations and the abundance of biocontrol agents. We found high genetic diversity across all sites, suggesting frequent recruitment from seed. Aphthona complex biocontrol agents were everywhere, but the association between agent abundance and leafy spurge density was not consistent. Increased population-level importance of seed production may be changing the most effective targets for biocontrol after decades of Aphthona pressure on leafy spurge invasions. Further testing is needed to ensure management tools, such as biocontrol, are sufficient for long-term sustainable control.

Technical Abstract: When weeds can reproduce both sexually and vegetatively, plant density and turnover can drive and be driven by the relative success of these co-occurring strategies. Such considerations are particularly important for sustained management with biological control (biocontrol), which relies on specialized herbivores that selectively target demographic processes to limit weed populations. We quantified genetic diversity, weed density, and associated biocontrol agent (Aphthona species complex) abundance in 100 Euphorbia virgata Waldst. & Kit. (leafy spurge) populations across three US states. This survey was intended to provide insight into: 1) the frequency of seedling recruitment among populations, which is strongly related to population genetic diversity in clonal plants such as E. virgata; and 2) the degree to which E. virgata density is related to inferred vegetative and seedling recruitment within local weed populations and the abundance of biocontrol agents. We found high genetic diversity across all sites, suggesting frequent recruitment from seed. Aphthona complex biocontrol agents were ubiquitous, but the association between Aphthona abundance and E. virgata density was variable. Increased population-level importance of seed production may be changing the priority of demographic targets for biocontrol after decades of Aphthona pressure on E. virgata invasions. Further empirical evaluation is needed to ensure management tools, such as biocontrol, are sufficient for long-term sustainable control.