Genetic rescue reduces mate limitation in a threatened, clonal, and self-incompatible plant species

Mate limitation is a restoration issue in self-incompatible plant species and can easily go undetected in clonal species when seed set is not directly measured. Populations experiencing mate limitation have low-to-no seed production, and therefore are not demographically viable. The only way to overcome mate limitation in an existing population is genetic rescue, while efforts to restore populations where mate limitation may be an issue should consider mixing source populations. While the merits and challenges of genetic rescue and mixing source populations have been widely debated in the literature, very few long-term examples are available to inform restoration actions. We hypothesized that remnant populations are experiencing mate limitation, while mixed-source populations are not. We tested mate limitation using three treatments: (1) open pollination; (2) controlled crosses within populations; and (3) controlled crosses between nearby populations (genetic rescue). We compared seed set and offspring fitness among cross treatments and by population type. We confirmed that remnant populations are experiencing mate limitation: seed set averaged only 13% with no genetic augmentation, while the genetic rescue treatment increased seed set by an average of 96%. However, for mixed-source populations, no differences were found for seed set with genetic rescue treatment. Offspring fitness did not significantly differ by cross treatment or population status. Results support local genetic rescue and mixed-sourcing as restoration tools for clonal, self-incompatible species.