Pollinators exert natural selection on flower size and floral display inPenstemon digitalis

Abstract

Summary• A major gap in our understanding of floral evolution, especially micro-evolutionary processes, is the role of pollinators in generating patterns of natural selection on floral traits. Here we explicitly tested the role of pollinators in selecting floral traits in a herbaceous perennial, Penstemon digitalis.• We manipulated the effect of pollinators on fitness through hand pollinations and compared phenotypic selection in open-and hand-pollinated plants.• Despite the lack of pollen limitation in our population, pollinators mediated selection on floral size and floral display. Hand pollinations removed directional selection for larger flowers and stabilizing selection on flower number, suggesting that pollinators were the agents of selection on both of these traits.• We reviewed studies that measured natural selection on floral traits by biotic agents and generally found stronger signatures of selection imposed by pollinators than by herbivores and co-flowering plant species.

Pollinators and nectar robbers cause directional selection for large spur circle in Impatiens oxyanthera (Balsaminaceae)

“…Corolla size affected pollinator attraction and showed significant heritability within natural populations (Campbell et al 1996;Gómez et al 2009), thus was under direct selection by pollinators (Galen 1989;Gong and Huang 2009;Sandring and Å gren 2009;Parachnowitsch and Kessler 2010;. As stated in previous findings, pollinators preferred flowers with large corolla in I. oxyanthera (Table 5; Fig.…”

“…If there was severe pollen limitation, selection on floral traits through pollinators would overwhelm selection through nectar robbers. Although we found that hand-pollinated flowers set 26 % more fruits than open-pollinated flowers (unpublished data), it was not suitable for all populations to employ pollen limitation as a predictor of the intensity of pollinator-mediated selection (Totland et al 1998;Parachnowitsch and Kessler 2010). As Irwin and Maloof (2002) found, the abundance of nectar-robbing varied in time and space in I. oxyanthera, thus the direction and intensity of selection on floral traits via pollinators and nectar robbers likely varies across time and space to maintain floral diversity.…”

Self‐ and intra‐morph incompatibility and selection analysis of an inconspicuous distylous herb growing on the Tibetan plateau (Primula tibetica)

“…Various flower traits are demonstrated to be selected for by pollen limitation, including flower size (Sletvold et al., 2010), flower number (Parachnowitsch & Kessler, 2010), flower color (Sletvold, Trunschke, Smit, Verbeek, & Ågren, 2016), inflorescence height (Ågren, Hellström, Toräng, & Ehrlén, 2013), spur length (Chapurlat et al., 2015; Sletvold & Ågren, 2010), and flower tube length (Alexandersson & Johnson, 2001). Severe pollen limitation selects for traits that increase the floral display (Ashman & Morgan, 2004) but also selects for traits that promote autonomous self‐fertilization (Morgan & Wilson, 2005; Porcher & Lande, 2005).…”

Pollinator-mediated natural selection inPenstemon digitalis

“…Moreover, we found that although there are few studies available that directly test whether pollinators are the agents of natural selection, selection on floral traits is generally stronger in the presence of pollinators than in their absence. 1 These results are important because they both empirically demonstrate that pollinators can and do act as agents of selection in the wild and that pollinator-mediated selection in…”

“…Moreover, when we compared pollinators to co-flowering plants (competitors or facilitators) and herbivores, we found that pollinators were a stronger agent of selection on floral traits. 1 A recent and comprehensive review of selection on floral traits indicates that phenotypic selection on floral characters is often sporadic, suggesting that pollinators are unlikely to be strong selective agents. 3 However, our review suggests that even with many non-significant selection coefficients, the general pattern is strong.…”