Mating System Evolution under Strong Pollen Limitation: Evidence of Disruptive Selection through Male and Female Fitness in Clarkia xantiana

Abstract

Selection on floral traits in hermaphroditic plants is determined by both male and female reproductive success. However, predictions regarding floral trait and mating system evolution are often based solely on female fitness. Selection via male fitness has the potential to affect the outcomes of floral evolution. In this study, we used paternity analysis to assess individual selfing rates and selection on floral traits via male and female fitness in an experimental population of Clarkia xantiana where pollen limitation of seed set was strong. We detected selection through both female and male fitness with reinforcing or noninterfering patterns of selection through the two sex functions. For female fitness, selection favored reduced herkogamy and protandry, traits that promote increased autonomous selfing. For male fitness, selection on petal area was disruptive, with higher trait values conferring greater pollinator attraction and outcross siring success and smaller trait values leading to higher selfed siring success. Combining both female and male fitness, selection on petal area and protandry was disruptive because intermediate phenotypes were less successful as both males and females. Finally, functional relationships among male and female fertility components indicated that selfing resulted in seed discounting and pollen discounting. Under these functional relationships, the evolutionarily stable selfing rate can be intermediate or predominantly selfing or outcrossing, depending on the segregating load of deleterious mutations.

From the Past to the Future: Considering the Value and Limits of Evolutionary Prediction

“…Apart from the issue of life span, it is often most convenient to assess fitness through maternity, ignoring paternal fitness variation because of the difficulty of attributing offspring to particular sires. It is now, however, feasible to assign paternity with considerable confidence (e.g., Kulbaba and Worley 2012;Briscoe Runquist et al 2017). With such information, FTNS could be applied using estimates based on either maternal fitness or paternal fitness.…”

The evolvability of animal‐pollinated flowers: towards predicting adaptation to novel pollinator communities

“…Finally, reduced reliability of pollination is often associated with shifts in mating systems (rate of self-pollination), and will typically involve changes in traits that confer reproductive assurance, notably herkogamy and dichogamy (e.g. Moeller, 2006;Dart et al, 2012;Opedal et al, 2016Opedal et al, , 2017Briscoe Runquist et al, 2017). Therefore, a predictive understanding of plant adaptation to novel pollinator communities will also require knowledge of variation in evolvabilities among trait groups.…”

Multiple aspects of the selfing syndrome of the morning glory Ipomoea lacunosa evolved in response to selection: A Qst‐Fst comparison

“…Studies of selection on self-pollination have estimated current levels of inbreeding depression, pollen discounting, and seed discounting (Busch & Delph, 2012;Husband & Schemske, 1996;Layman, Fernando, Herlihy, & Busch, 2017;Rausher, Augustine, & Vanderkooi, 1993), and whether selfing is favored in conditions of pollen or pollinator limitation (Briscoe Runquist, Geber, Pickett-Leonard, & Moeller, 2017;Fishman & Willis, 2008;Gervasi & Schiestl, 2017;Moeller & Geber, 2005;Roels & Kelly, 2011;Strandh et al, 2017;Toräng et al, 2017). However, we know of fewer direct demonstrations of overall selection favoring selfing, although a recent study in Leavenworthia found molecular signatures consistent with positive selection on the S-locus (Herman & Schoen, 2016).…”