Resource reallocation does not influence estimates of pollen limitation or reproductive assurance in Clarkia xantiana subsp. parviflora (Onagraceae)

Premise of study: Studies of pollen limitation and the reproductive assurance value of selfing are important for examining the process of floral and mating system evolution in flowering plants. Recent meta-analyses have shown that common methods for measuring pollen limitation may often lead to biased estimates. Specifically, experiments involving single- or few-flower manipulations per plant tend to overestimate pollen limitation compared to those involving manipulations on most or all flowers per plant. Little previous work has explicitly tested for reallocation within individual systems using alternative methods and response variables. Methods: We performed single-flower and whole-plant pollen supplementation and emasculation of flowers of Clarkia xantiana subsp. parviflora to estimate pollen limitation (PL) and reproductive assurance (RA). We compared levels of PL and RA using the following response variables: fruit set, seeds/flower, and seeds/plant. We also assessed the germination and viability of seeds to evaluate potential variation in pollen quality among treatments. Key results: Autonomous selfing in Clarkia xantiana subsp. parviflora eliminates pollen limitation and provides reproductive assurance. Estimates from single-flower manipulations were not biased, closely resembling those from whole-plant manipulations. All three response variables followed the same pattern, but treatments were only significantly different for seeds/flower. Pollen quality, as indicated by seed viability, did not differ among treatments. Conclusions: Partial plant manipulations provided reliable estimates of pollen limitation and reproductive assurance. These estimates were also unaffected by accounting for pollen quality. Although whole plant manipulations are desirable, this experiment demonstrates that in some systems partial plant manipulations can be used in studies where whole-plant manipulations are not feasible.