No abstract

Background: It has long been known that rates of synonymous substitutions are unusually low in mitochondrial genes of flowering and other land plants. Although two dramatic exceptions to this pattern have recently been reported, it is unclear how often major increases in substitution rates occur during plant mitochondrial evolution and what the overall magnitude of substitution rate variation is across plants.

A hypothesis is presented which states that flower production in hermaphroditic flowering plants is primarily controlled by male function. The male function hypothesis predicts a lower fruit—to—flower ratio for hermaphrodites as compared to monoecious or dioecious plants. The hypothesis also predicts that self—compatible hermophrodites should exhibit a higher percent fruit—set than self—incompatible hermaphrodites. These predictions are supported by fruit—set data complied from the literature. An alternative hypothesis relating fruit—set to the probability of self—fertilization also predicts low fruit—set for hermaphrodites as compared to monoecius or dioecious plants. The self—incompatibility hypothesis is tested and rejected on the basis of fruit—set patterns in self—incompatible andromonoecious, self—incompatible monoecious, and self—compatible monoecious species. The effect of the male function hypothesis on current ideas concerning low fruit—set in hermaphrodites is then examined.

No abstract

The transmission advantage and reproductive assurance ideas describe components of gene transmission that favour selfing. Future work should move beyond their dichotomous presentation and focus upon understanding whether selection through pollen, seed or both explains the spread of selfing-rate modifiers in plant populations.