Contributions of autogamy and geitonogamy to self-fertilization in a mass-flowering, clonal plant

The fitness consequences of self-fertilization are largely determined by ho w self-pollination occurs. Within-flower self-pollination (autogamy) may be advantageous, since it can provide reproductive assurance without much see d or pollen discounting. In contrast, between-flower self-pollination (geit onogamy) provides no reproductive assurance and can cause severe seed and p ollen discounting. I used floral emasculations with marker gene analysis to estimate the components of self-fertilization ina tristylous, self-compati ble, clonal, mass-flowering plant, Decodon verticillatus. This species prod uces 30% of progeny through selfing. I assessed the contribution of autogam y to selling by comparing pollen deposition, seed production, and the selfi ng rate of flowers emasculated before anther dehiscence with intact flowers . Emasculation had no effect on pollen deposition, caused a small increase in seed production, and only reduced self-fertilization by 14%, suggesting that most selfing occurs through geitonogamy. Geitonogamy can be due to sel f-pollination between flowers on the same branch, different flowering branc hes of the same plant, or different ramets of the same clonal genet. I asse ssed the contribution of within-branch geitonogamy by emasculating all flow ers on a branch, which reduced selfing from 0.29 +/- 0.03 (mean +/- 1 SE) t o 0.19 +/- 0.04. Between-branch geitonogamy was estimated by comparing the selfing rate of plants with only a single flowering branch (0.16 +/- 0.07) to plants with multiple flowering branches (0.27 +/- 0.04). Selfing rates o f individual branches also correlated positively with the daily number of f lowers open on nonfocal branches of the same plant. Between-ramet geitonoga my was suggested by significant self-fertilization by single-branch plants, even when all flowers were emasculated (0.10 +/- 0.07). Selfing rates of i ndividual branches also correlated negatively with measures of local clonal diversity. Based on these results, autogamy accounts for only 18 +/- 14% o f self-fertilization, with the remainder (82 +/- 17%) due to geitonogamy, w hich occurs about equally through pollination within branches (31 +/- 22%), between branches (38 +/- 32%), and between ramets (31 +/- 28%). Because se lfing occurs mostly through geitonogamy and is associated with strong inbre eding depression, it seems disadvantageous. Selfing in D. verticillutus has probably not been selected directly, but is a by-product of self-compatibi lity, large plant size, mass-flowering, and clonal propagation.