Sex morphs and invasiveness of a fleshy-fruited tree in natural grasslands from Argentina

Invasiveness has usually been studied as a species-level attribute; nevertheless, phenotypic differences between individuals in a population can lead to significant variations in colonization ability. In this paper, we analyse the potential effects of sex morphs of Prunus mahaleb L., a gynodioecius fleshy-fruited tree, on its invasiveness in natural grasslands in the southern Argentine Pampas. We assessed the abundance of both hermaphrodite and female plants, and compared their fecundity, propagule size, and germination response. We found that the females were less abundant in the invasive populations studied, apparently since the beginning of the colonization. However, our results demonstrated that at the present time, females do not show any fecundity reduction, which clearly shows that P. mahaleb has established an effective interaction with generalist pollinators that compensates for the apparently disadvantaged females. Fruit set showed a wider range of variability over time in the females than in the hermaphrodites, which could be the consequence of greater susceptibility to changes in the activity of pollinators. We found no evidence of a female benefit due to reallocation of resources or better outcrossed progeny when considering propagule size and germination. We discuss the relative importance of sex morphs and interactions at different stages of the invasion process.