EFFECT OF POLLEN COMPETITION ON OFFSPRING QUALITY AT VARYING STAGES OF THE LIFE-CYCLE IN SILENE LATIFOLIA POIRET (CARYOPHYLLACEAE)

A critical stage in the life cycle of flowering plants occurs during p ollen germination and pollen tube growth. When pollen tubes outnumber available ovules, competition among pollen gains occurs. Under such co nditions, it has been suggested that an increase in progeny fitness ma y occur. In Silene latifolia Poiret (Caryophyllaceae), the adaxial sur face of the long styles is receptive to pollen germination. As a resul t, the intensity of pollen competition can be manipulated by placing p ollen at various distances from the ovary. We performed an experiment in which we placed excess pollen at one of two distances from the ovar y. We then compared seed, seedling, and adult characters of the progen y resulting from these two treatments. Pollen placement had a statisti cally significant: effect on adult sex ratio, with progeny resulting f rom more intense pollen competition containing a statistical excess of males, and progeny resulting from less intense competition containing a nonsignificant: excess of females. Pollen placement did not have a statistically significant effect on any of seven measures of offspring quality (seed number per fruit, mean seed mass, seedling emergence ti me, cotyledon area after two weeks, leaf area after four weeks, above- ground dry weight after six weeks, and days required to flower). Since one of our dependent variables (seedling emergence time) was found to be significantly affected by pollen competition in an earlier study, it appears that such traits may be as much influenced by parental, env ironmental, or population-level effects as by pollen competition.