Effect of Pollination and Postpollination Processes on Selfing Rate

Abstract

Selfing rates vary widely within and among populations of self compatible flowering plants. This variation is often attributed to differences in the amount and timing of self and outcross pollen deposition on stigmas, as well as to the influence of postpollination mechanisms that control pollen siring success. This study explores the relative importance of pollination and postpollination processes in determining selfing rates in monkeyflower, Mimulus ringens. We hand-pollinated flowers on each of 17 unrelated mothers with pollen from one of three experimental treatments intended to replicate field conditions: 1) Simultaneous deposition of 50% self pollen and 50% outcross pollen from 5 unrelated donors. 2) Self pollen followed 15 min later by application of an equal amount of outcross pollen from 5 unrelated donors. 3) Outcross pollen from 5 unrelated donors followed 15 min later by application of an equal amount of self pollen. We genotyped 757 progeny at 8 polymorphic microsatellite loci and used paternity exclusion to determine whether each seedling was self or outcross. When self and outcross pollen arrived simultaneously, observed proportions of self and outcross progeny did not deviate from the expected 1:1 ratio. However, when outcross pollen was applied 15 min prior to self pollen, there was a significant excess of outcross progeny. Selfing rate in Mimulus ringens is influenced by the timing of pollen arrival, but not by non-random postpollination sorting.