Format: ORAL

Mai Thu Nguyen,John R. Pannell

Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne.

The co-existence of females, males and hermaphrodites (trioecy) is rare in both plants and animals, and the few cases that do exist are poorly understood. Here, we provided a new model explaining the stable coexistence of these three sexual phenotypes. In contrast with previous models, which investigate the invasion of a hermaphroditic population by cytoplasmic male sterility (CMS), our model considers the invasion of CMS into a population in which males and hermaphrodites already coexist (androdioecy). We compared the invasion and fixation of CMS in androdioecious versus hermaphroditic populations and show that the existence of males prior to CMS invasion facilitates the maintenance of trioecy even in the absence of pollen limitation though pollen limitation does also promote the maintenance of trioecy under certain conditions. We discuss these results with reference to the case of trioecy in the annual plant Mercurialis annua and consider trioecy as a possible evolutionary path from hermaphroditism and dioecy.