Mercurialis annua hexaploid hermaphrodites typically resemble females in their inflorescence architecture, bearing their subsessile inflorescences on the leaf axils. Males, on the other hand, produce a large amount of flowers displayed along long peduncles that protrude above the canopy. Given that Mercurialis annua is a wind pollinated species, peduncles provide important benefits for pollen dispersal. So if males show this adaptation, why hermaphrodites don’t? Excitingly, several populations of hermaphrodites bearing male-like peduncles have been recently found in eastern Spain. They co-occur in the same range as previously known hermaphrodites, and this discovery poses a number of exciting questions relevant to the ecology of wind pollination: What are the fitness consequences of bearing male flowers on peduncles? Do genes coding for peduncles have pleiotropic effects? Are there trade-offs with other fitness traits? What is the genetic architecture of inflorescence architecture? Are males less likely to invade pedunculate hermaphrodite populations? Will pedunculate hermaphrodite populations expand their range? We are currently addressing these questions by phenotypic and molecular characterization, controlled crosses and mating array experiments.
Preliminary analyses for the gene flow experiment have been completed. This experiment, conducted by postdoc Anne-Marie Labouche, considers the effects of pollen limitation and pollen competition on offspring number and quality as a function of plant density. Apart from demonstrating pollen limitation in Mercurialis, the experiment showed larger pollen flow distances than expected and several other interesting features related to M. annua mating system.