Environmental stress effects on reproduction and sexual dimorphism in the gynodioecious species Silene acaulis

In gynodioecious species, hermaphrodite plants invest both in seed and pollen production, whereas female plants only produce fruits. For both sexes to coexist, such unbalanced investment is expected to translate in some kind of reproductive compensation, particularly under severe nutrient shortage or environmental stress. This study investigates 1) whether females of the gynodioecious boreo-alpine plant Silene acaulis show any overall compensation in fitness components; 2) the existence of sexual dimorphism in flowers that favor different modes in each sex; 3) whether environmental severity, characterized by means of a Species Distribution Model, strength these patterns. Flower size, fruit and seed production, and germination success were recorded in six populations across the Pyrenees and the Alps. Fruit set was significantly higher in female (59%) than in hermaphrodite plants (17%), and female organs (ovary and style) were larger in female than in hermaphrodite plants, but female flowers were smaller. Contrary to expectations, environment severity was not related with most of the biological traits studied and only germination was associated to environmental gradients. These results confirm that fruit production plays an important role as a compensatory strategy between sexes and, consequently, may favor the presence of both sexes in a gynodioecious species.