DOES SELF-POLLINATION PROVIDE REPRODUCTIVE ASSURANCE IN AQUILEGIA-CANADENSIS (RANUNCULACEAE)

The ability to produce seeds when pollinators or potential mates are s carce is thought to be one of the main advantages of self-fertilizatio n in flowering plants. However, whether autonomous selfing increases s eed set in natural populations has seldom been tested, and even fewer studies have evaluated the advantage of selfing across a gradient of p ollen availability. This study examines the fertility consequences of autonomous selfing in Aquilegia canadensis (Ranunculaceae), a short-li ved, spring-flowering perennial typically found in small, patchy popul ations on rock outcrops. We used a pollinator exclusion experiment to confirm reports that A. canadensis has a well-developed capacity for a utonomous selfing resulting from incomplete protogyny and close proxim ity of stigmas and anthers during dehiscence. Flowers excluded from po llinators set 87% as many seeds per carpel (X +/- 1 SE = 7.1 +/- 1.4 s eeds) as hand-pollinated flowers (8.1 +/- 1.3 seeds), and seed product ion in unpollinated flowers correlated negatively with the distance be tween stigmas and anthers (r = -0.46). Autonomous selfing could be pot entially valuable in providing reproductive assurance because only 2.7 +/- 0.5 pollen grains were deposited on each stigma before anther deh iscence, compared to 134.1 +/- 17.9 pollen grains by the end of anther dehiscence. However, prevention of autonomous selfing by anther remov al before dehiscence did not decrease seed set, even for plants at low plant densities where outcross pollen may have been in short supply. Emasculated flowers set as many seeds per carpel (9.3 +/- 0.9) as inta ct flowers (8.4 +/- 1.1), indicating that sufficient cross pollen is d eposited for full seed set. These results do not support the hypothesi s that autonomous selfing by A. canadensis has been selected because i t provides reproductive assurance.