Premise: The timing of self-fertilization has potentially important consequences for the trajectory of mating system evolution, the opportunity for outcrossing, and the maintenance of genetic variation in populations. For primarily selfing taxa, it remains poorly understood as to how floral variation influences the opportunity for outcrossing and whether those attributes vary among populations across geographic ranges. Methods: We examined variation in floral traits (herkogamy, protandry, flower size, stigma stage at anthesis, timing of stigma receptivity) in seven populations of Clarkia xantiana ssp. parviflora, a primarily selfing taxon, spanning from the western to eastern margins of its distribution. We also performed experimental emasculations and pollinations (followed by stigma severing) to quantify the extent of opportunities for outcrossing across flower development. Results: There was marked among-population variation in all floral traits, particularly between far eastern and western populations. Emasculation experiments showed that the eastern populations had minimal autonomous selfing, but western populations had high rates of selfing within 24 h after anthesis. Population variation in autofertility was significantly predicted by floral trait variation, especially protandry and petal size. Conclusions: Greater protandry both extended the time over which outcrossing could potentially occur and reduced the probability of autonomous selfing, suggesting that there may be a tradeoff that results in fitness loss when pollinator visits are not common. The east-west pattern of differentiation in some floral traits parallels that of postglacial range expansion, suggesting that selection on the mating system may have been strong in the process of range expansion.
Bibliographical noteFunding Information:
The authors thank Leslie Clements, Diane Hunt, Kelsey Smith, and Morgan Wall for assisting with data collection and plant care throughout the experiment. We also thank the anonymous reviewers for providing very helpful comments on an earlier version of this manuscript. This project was funded by the CNU Summer Scholars Program and NSF DEB‐1025004 to DAM (including ROA supplement).
© 2020 Botanical Society of America
- breeding systems
- geographic variation
- mating system evolution
- mixed mating strategy
- range expansion
- sexual selection
PubMed: MeSH publication types
- Journal Article
- Research Support, U.S. Gov't, Non-P.H.S.