INBREEDING DEPRESSION IN ANDRODIOECIOUS POPULATIONS OF DATISCA-GLOMERATA (DATISCACEAE)

Several workers have suggested that the rarity of androdioecy (the pre sence of males and hermaphrodites in a breeding population) in nature is due to the large fitness gain required by male plants in order to b e maintained by selection. As part of an ongoing investigation of this hypothesis, we tested the effects of selfing on fitness in functional ly androdioecious populations of Datisca glomerata. We compared progen y from self-fertilizations, cross-fertilizations with pollen from male plants only, cross-fertilizations with pollen from hermaphrodite plan ts only, and open-pollinated flowers for several measures of progeny f itness including seed weight, germination rate, and seedling weight. S ignificant inbreeding depression was observed for androdioecious popul ations of D. glomerata for both seed and seedling weights. However, no significant differences were observed across treatments for seed germ ination percentages. The observation of significant levels of inbreedi ng depression in this study, combined with prior evidence of threefold greater pollen production by males, may at least partially account fo r the large fitness increase required by males to be maintained by sel ection.