Self-Incompatibility inUlex europaeus: Variations in Native and Invaded Regions

Premise of research. The mating systems of introduced plant species are important components of their invasive success because they can favor reproductive assurance during the colonization process. The hypothesis known as Baker’s rule implies that colonizing species should evolve toward a lower dependence on pollinators, a higher self-fertility, and a lower inbreeding depression. Here, we test these predictions by comparing the mating system of the perennial shrubUlex europaeus(Fabaceae) in regions from its native and invaded ranges. Methodology. We performed controlled pollinations on plants from two regions of origin (Brittany and Scotland) and two invaded regions (New Zealand and Reunion) grown in a common garden. We tested the possibility of autonomous pollination; estimated the relative seed set of selfing versus outcrossing; and recorded the viability, mass, and germination capacity of the seeds produced. Pivotal results. Ulex europaeuscannot set seeds in the absence of active pollination. Seed set after selfing was lower than seed set after outcrossing, indicating that the species is partly self-incompatible. The level of self-compatibility was highly variable depending on the individuals, but native and invaded regions exhibited similar levels of self-fertility. Early inbreeding depression was very low in both native and invaded regions. Seed mass and germination velocity were higher in the invaded regions than in the native regions. Conclusions. Reproductive traits linked with reproductive assurance (autonomous pollination, self-fertility, inbreeding depression) were similar in native and in introduced regions, which does not support the predictions of Baker’s rule. The study, however, reveals that plants from the invaded regions exhibit higher values for seed traits related to competitive ability at early stages. These results can be explained by the life history of gorse and by the history of its introduction in the invaded regions.