Pollen colour morphs take different paths to fitness

Abstract

Colour phenotypes are often involved in communication and are thus under selection by species interactions. However, selection may also act on colour through correlated traits or alternative functions of biochemical pigments. Such forms of selection are instrumental in maintaining petal colour diversity in plants. Pollen colour also varies markedly, but the maintenance of this variation is little understood. In Campanula americana, pollen ranges from white to dark purple, with darker morphs garnering more pollinator visits and exhibiting elevated pollen performance under heat stress. Here, we generate an F2 population segregating for pollen colour and measure correlations with floral traits, pollen attributes and plant‐level traits related to fitness. We determine the pigment biochemistry of colour variants and evaluate maternal and paternal fitness of light and dark morphs by crossing within and between morphs. Pollen colour was largely uncorrelated with floral traits (petal colour, size, nectar traits) suggesting it can evolve independently. Darker pollen grains were larger and had higher anthocyanin content (cyanidin and peonidin) which may explain why they outperform light pollen under heat stress. Overall, pollen‐related fitness metrics were greater for dark pollen, and dark pollen sires generated seeds with higher germination potential. Conversely, light pollen plants produce 61% more flowers than dark, and 18% more seeds per fruit, suggesting a seed production advantage. Results indicate that light and dark morphs may achieve fitness through different means—dark morphs appear to have a pollen advantage whereas light morphs have an ovule advantage—helping to explain the maintenance of pollen colour variation.

Geographic Variation in Floral Color and Reflectance Correlates With Temperature and Colonization History

“…Thus, the color metrics of petals from this study cannot be easily compared to the pollen color scored in Koski and Galloway (2018) . Regardless, given the strong longitudinal cline in pollen color, there is the potential that historical colonization has played a role in structuring pollen color as well as petal color despite a lack of genetic correlation between the two ( Koski et al., 2020 ).…”

“…Thus, color variation has the ability to impact pollinator choice. Pollen color and petal color are not genetically correlated (Koski et al, 2020).…”

“…It is pollinated by bumblebees which are very effective at pollen transfer, and small solitary bees that are relatively ineffective pollinators ( Koski et al., 2018 ). It displays variation in pollen coloration that is genetically uncorrelated with petal color ( Koski and Galloway, 2018 ; Koski et al., 2020 ). Geographic patterns of petal coloration have not been evaluated.…”

Map-based cloning of the APRR2 gene controlling green stigma in bitter gourd (Momordica charantia)

“…There is general agreement that the diversity of flower colors in angiosperms is mostly determined by variation in the interactions with pollinators via natural selection, in part because pollinators tend to enhance assortative mating ( Gervasi and Schiestl, 2017 ; Trunschke et al., 2021 ). In addition to the most visible petal color, other types of flower colors include pollen, gynoecium and inflorescence colors polymorphisms ( Carlson and Holsinger, 2010 ; Koski et al., 2020 ). The color of stigma may also differ across plant varieties and be distinguishable from the petal background to attract pollinators, such as tulip, melon, and sunflower, which may further enhance the crop production ( Miklič et al., 2002 ; Miller et al., 2011 ; Lv et al., 2022b ).…”

Interactive effects of changes in UV radiation and climate on terrestrial ecosystems, biogeochemical cycles, and feedbacks to the climate system

“…There is also evidence that greater accumulation of flavonoids in pollen grains improves their germination (e.g. in Clarkia unguiculate ; [ 181 ]) and flavonoids function in UV screening in pollen, which is essential to maintain viability [ 182 , 183 ]. Additionally, flavonoid glycosides (quercetins and kaempferols), hydroxycinnamic acids and anthocyanins in leaves and pollen act as strong antioxidants, and, as such, they scavenge reactive oxygen species (ROS) produced by abiotic stressors such as excessive solar radiation, including UV-B radiation [ 178 , 184 ].…”