The Mercurialis seed collection at UNIL (Switzerland) has been enriched this month by the arrival of three woody Mercurialis species collected in the Iberian Peninsula: Mercurialis elliptica, M. tomentosa y M. reverchonii, the two latter with a restricted distribution to SW Iberian Peninsula and NW Africa. These three species are described as dioecious and could provide an interesting outgroup placed at between monoecious Euphorbiaceae (such as Ricinus communis, the castor-oil plant) and dioecious Mercurialis annua. A male and a female of each species will also be added to the gene capture experiment, providing comparative genomic data for male and female sex-linked regions across Mercurialis genus.
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.