The functional significance of synchronous protandry in Alstroemeria aurea

Abstract

1. Synchronous dichogamy, the simultaneous change in sex phases of all flowers in an inflorescence or entire plant, has been proposed to reduce self-pollination between flowers within a plant (geitonogamy) and so should leave more pollen for export and/ or reduce inbreeding. We tested these hypotheses with Alstroemeria aurea Graham, a self-compatible, clonal herb with synchronous protandrous inflorescences. 2. We manipulated A. aurea inflorescences to compare pollen export, pollen receipt and pollen-tube attrition in synchronous and asynchronous inflorescences. We constructed asynchronous inflorescences by tying together female- and male-phase ramets which were collected within 1 m of each other and so had a high probability of being genetically related. 3. Inflorescences with both male- and female-phase flowers received 27% more pollen than synchronous inflorescences, which was associated with higher pollen-tube attrition. The selfing suggested by these results would reduce genetic contributions to the next generation as a result of the strong inbreeding depression found in this species. 4. In contrast, we found no evidence that asynchronous inflorescences exported less pollen to companion female-phase inflorescences than did synchronous inflorescences. 5. Our results suggest that synchronous dichogamy evolves primarily as an anti-selfing mechanism, rather than to promote outcross siring success.