SEXUAL DIMORPHISMS AND RESPONSE TO LOW RESOURCES IN THE DIOECIOUS PLANT SILENE LATIFOLIA (CARYOPHYLLACEAE)

Females of dioecious species often have higher reproductive effort than males because of their production of fruits. We postulated that females of Silene latifolia would reduce growth or reproductive effort to a greater extent than males when grown under conditions of low resource availability. To test this hypothesis, plants were grown in pots divided into 11 treatments: high levels of resources (controls) and medium or low levels of light, water, nitrogen, phosphorus, and potassium. There were more females than males in all of the treatments but there was no variation in sex ratios among treatments. Females produced larger, but fewer, flowers than males. The number of flowers in both sexes was correlated with the values of many sexually dimorphic traits, including plant height, length of inflorescence branches, total biomass, reproductive biomass, and percent allocation to leaves, branches, and reproduction. Females had higher reproductive effort than males in all treatments and invested more biomass per length in their main stem. Females also invested more biomass per length in their inflorescence branches, probably as a consequence of branch architecture. Phenotypic correlations, plant morphology, and growth varied in response to the different environmental treatments, but males and females did not respond differently to low resource availability. Two hypotheses are presented to explain these results, which are contrary to the expectation that females of dioecious species are more adversely affected than males when resources are limiting.