Inbreeding and outbreeding effects on pollen fitness and zygote survival in Silene nutans (Caryophyllaceae)

In plants, selfing and outcrossing may be affected by maternal mate choice and competition among pollen and zygotes. To evaluate this in Silene nutans , we pollinated plants with mixtures of (1) self- and outcross pollen and ( 2) pollen from within a population and from another population. Pollen fitn ess and zygote survival was estimated from the zygote survival and paternit y of seeds. Self pollen had a lower fitness than outcross pollen, and selfe d zygotes were less likely, or as likely, to develop into seeds. Hybrid zyg otes survived as frequently or more than local zygotes, and pollen from one of the populations fertilized most ovules in both populations. Our results thus indicate strong maternal discrimination against selfing, whereas the success of outbreeding seems mostly affected by divergent pollen performanc e. The implications for the evolution of maternal mate choice are discussed .