How early does the selfing syndrome arise? Associations between selfing ability and flower size within populations of the mixed‐mater Collinsia verna

Abstract

Premise: Widespread associations between selfing rate and floral size within and among taxa suggest that these traits may evolve in concert. Does this association develop immediately because of shared genetic and/or developmental control, or stepwise with selection shaping the evolution of one trait following the other? If the former, then association ought to appear within and across selfing populations. We explore this fundamental question in three populations of the mixed-mater Collinsia verna where autonomous selfing (AS) ability has been shown to be under selection by the pollination environment. Methods: We grew clonal replicates of C. verna in a controlled environment to characterize broad-sense genetic correlations among traits within populations and to assess whether divergence in mating system and floral traits among these populations is consistent with their previously observed selection pressures. Results: As predicted by their respective pollination environments, we demonstrate significant genetic divergence among populations in AS ability. However, patterns of divergence in floral traits (petal, stamen, and style size, stigmatic receptivity, and stigma-anther distance) were not as expected. Within populations, genetic variation in AS appeared largely independent from floral traits, except for a single weak negative association in one population between flower size and AS rate. Conclusions: Together, these results suggest that associations between selfing rate and floral traits across Collinsia species are not reflected at microevolutionary scales. If C. verna were to continue evolving toward the selfing syndrome, floral trait evolution would likely follow stepwise from mating system evolution.

Continuous inbreeding affects genetic variation, phenology, and reproductive strategy in ex situ cultivated Digitalis lutea

“…Flower size is an important trait known to attract more pollinators (Galen and Newport, 1987; Conner and Rush, 1996; Goodwillie et al, 2010) and allows more spatial separation between anthers and stigmas, reducing the risk of selfing (Barrett, 2003, Herlihy and Eckert, 2007; Luo and Widmer, 2013). In contrast, a reduction of flower size is a typical part of the selfing syndrome (Sicard and Lenhard, 2011; Wright et al, 2013; Cutter, 2019; McElderry et al, 2022). Flower size can become particularly small in flowers capable of autogamous selfing, whereas self‐pollination mediated by insects would still require attracting pollinators (Sicard and Lenhard, 2011; Salces‐Castellano et al, 2016).…”

“…However, in contrast to predictions of simple models, there is not necessarily a binary division between selfing and outcrossing, but a variety of influencing factors can favor mixed mating (de Jong and Klinkhamer, 2005). Small changes in such influences—in particular, the magnitude of ID and pollinator abundance—can change the benefit of investment into structures attracting pollinators and move populations of self‐compatible species more toward the selfing or the outcrossing end of a mixed‐mating gradient (Chang and Rausher, 1999; Kalisz et al, 2004, but see McElderry et al, 2022). Low ID can induce a higher reliance on self‐pollination, which may have advantages for plants when pollinators are scarce (reproductive assurance, Lloyd, 1992), but in the long term poses a threat to genetic diversity.…”

Changes in female function and autonomous selfing across floral lifespan interact to drive variation in the cost of selfing

“…Interestingly, we found a significant random population effect on autonomous seed number (Appendix S2), though we cannot determine with the data in hand whether the statistical significance of the random population term is meaningful with respect to variation in population reliance on reproductive assurance in the wild, potentially reflecting past evolution on autonomous selfing. Future work can investigate the extent to which genetically based population variation in autonomous selfing and its timing are connected to herkogamy or dichogamy and either pollination or abiotic conditions in the wild (e.g., Elle et al, 2010; Koski et al, 2018; McElderry et al, 2022).…”