Plasticity and within plant sex-ratio variation in monoecious Emex spinosa

Understanding how phenotype trait expression varies at different levels of biological organization is crucial to understanding the fundamental ecological, evolutionary, and developmental issues that contribute to adaptive plasticity. This is particularly important in plants because of their modular organization. Here, we study plasticity in flower production in response to light intensity at 3 levels of biological organization (between populations, among individuals, and within individuals) in Emex spinosa (L.) Compd., a Mediterranean amphicarpic annual. Plants exposed to high light intensity grew faster and produced more flowers than plants at low light intensity. Female flower production was the most labile trait. Within individuals, the production of female and male flowers, and the floral sex ratio strongly varied along the stems. Light intensity only significantly affected flower production at central and terminal positions in the inflorescence, while sex ratio was invariable to light intensity in each position, reflecting a sexual specialization independently of light, from initial femaleness towards maleness at the end of flowering. In Emex spinosa, the production of selfing fruits seems not only to concern ground fruits, but also early aerial fruits.