Evolution of Self-Pollination in Granite Outcrop Species of Arenaria (Caryophyllaceae). III. Reproductive Effort and Pollen-Ovule Ratios

Patterns of resource allocation and pollen-ovule ratios were measured in nine pop- ulations of Arenaria uniflora, a winter annual endemic to rock outcrops in the southeastern United States. Dry weights of plants from cross-pollinating populations were greater than those from self- pollinating populations for both vegetative and reproductive biomass. Reproductive effort (pro- portion of total biomass represented by reproductive structures), however, was greater for selfers. Pollen-ovule ratios showed a close fit to expectations: low pollen-ovule ratios are associated with low rates of outcrossing (assessed in terms of degree of protandry). Number of pollen grains per flower and pollen-ovule ratios show no variation between years and little variation within and among flowers or plants. Number of ovules per ovary is less stable. It is suggested that use of pollen-ovule ratios obscures the evolutionary dynamics of forces influencing pollen grain number and ovule number. Pollen and ovule production should be studied as separate, and potentially