Natural selection on floral traits of Caltha scaposa (Ranunculaceae), an alpine perennial with generalized pollination system from Northwest Yunnan

Abstract

Floral traits, including those invisible to humans but visible to pollinators, that increase pollination efficiency may be selected by pollinators in plant species with pollen limitation of seed production, but the importance of pollinators as selective agents on different floral traits needs to be further quantified experimentally. In the present study, we examined selective strength on flower diameter, flower height, UV bulls-eye size, sepal size and UV proportion via female fitness in Caltha scaposa, based on open-pollinated and hand-pollinated flowers, through which pollinator-mediated selection was calculated for each of floral traits. Our results suggest that seed production of C. scaposa is pollen limited in natural conditions. There was directional selection (Δβpollinator = −0.12) for larger flowers in open-pollinated flowers, while no significant selection was found in flower height, UV bulls-eye size, sepal size or UV proportion. Statistically significant selection was found in UV bulls-eye size, sepal size and UV proportion in hand-pollinated flowers, but interactions with pollinators contributed only to flower diameter. We conclude that in C. scaposa, floral traits that are subjected to selection might be driven by multiple selective agents, and suggest the importance of investigating floral traits that are invisible to human but visible to pollinators in measuring pollinator-mediated selection via male fitness.

Flower Color Evolution and the Evidence of Pollinator-Mediated Selection

“…Yet, we are aware of only 18 studies that aimed to quantify selection on continuous variation in petal coloration in the context of pollination ( Tables 1 , 2 ). Moreover, of these studies, only six used a hand-pollination treatment to estimate selection gradients associated with pollinator interactions ( Caruso et al, 2010 ; Parachnowitsch and Kessler, 2010 ; Lavi and Sapir, 2015 ; Sletvold et al, 2016 ; Zhang et al, 2017 ; Souto-Vilarósa et al, 2018 ; Supplementary Table 3 ). Some other studies used modeling approaches linking the flower color phenotype - fitness relationship to pollinator visitation data to determine the contribution of pollinators to observed total selection (e.g., Veiga et al, 2015 ; Rodriguez-Castañeda et al, 2020 ; Brunet et al, 2021 ; Supplementary Table 3 ).…”

“…Further, trait manipulation experiments have demonstrated that masking of flower nectar guides significantly reduced pollinator visits ( Hansen et al, 2012 ). However, details of color patterning as potential target of selection by pollinators have rarely been evaluated (but see Medel et al, 2003 ; Parachnowitsch and Kessler, 2010 ; Parachnowitsch et al, 2012 ; Sletvold et al, 2016 ; Zhang et al, 2017 ). That both Medel et al (2003) and Sletvold et al (2016) found significant selection on traits related to color patterning within flowers ( Tables 2 , 3 ) supports the view of their relevance for pollinator foraging decisions or pollination efficiency, and therefore may be more important than primary hue for pollinators selecting on flower color.…”

Origins and evolution of plant diversity in the Hengduan Mountains, China

“… Zhang et al. (2017) examined natural selection of floral traits via female fitness in Caltha scaposa , an alpine perennial with a UV bullseye.…”

Phenotypic Selection in Halenia elliptica D. Don (Gentianaceae), an Alpine Biennial with Mixed Mating System

“…The global decline in pollinator diversity could result in limited pollination for seed production [ 5 , 6 , 7 , 8 , 9 , 10 ], although several case studies have not found decreased seed production in wild plants in recent decades [ 11 , 12 ]. However, for outcrossing plants, the plant traits that are associated with pollinator attraction (e.g., plant height, flower time, flower size, flower tube depth, and flower number) and pollination efficiency (e.g., spur length) might be selected [ 13 , 14 , 15 , 16 , 17 , 18 ]. For example, pollinator-mediated selection may result in tall plants, plants with large flowers, more flowers, deep flower tubes, and long spurs, which are often reported in many plant species [ 14 , 17 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ].…”