Macroecological patterns in flower colour are shaped by both biotic and abiotic factors

Abstract

There is a wealth of research on the way interactions with pollinators shape flower traits. However, we have much more to learn about influences of the abiotic environment on flower colour. We combine quantitative flower colour data for 339 species from a broad spatial range covering tropical, temperate, arid, montane and coastal environments from 9.25°S to 43.75°S with 11 environmental variables to test hypotheses about how macroecological patterns in flower colouration relate to biotic and abiotic conditions. Both biotic community and abiotic conditions are important in explaining variation of flower colour traits on a broad scale. The diversity of pollinating insects and the plant community have the highest predictive power for flower colouration, followed by mean annual precipitation and solar radiation. On average, flower colours are more chromatic where there are fewer pollinators, solar radiation is high, precipitation and net primary production are low, and growing seasons are short, providing support for the hypothesis that higher chromatic contrast of flower colours may be related to stressful conditions. To fully understand the ecology and evolution of flower colour, we should incorporate the broad selective context that plants experience into research, rather than focusing primarily on effects of plant-pollinator interactions.

Changing How Biologists View Flowers—Color as a Perception Not a Trait

“…evidences an effect of both experience and conditioning on perception of floral color difference by a pollinating bee. This result thus indicates that though a flower's reflectance spectrum can be considered as a functional trait in some circumstances (Dalrymple et al, 2020), its interpretation by the brain of a pollinator cannot. Therefore, the color sensation experienced by a bee is frequently context dependant, and as such, cannot be quantified and compared as other purely physical traits.…”

“…When applied to plants, such as comparative studies testing for an association between colors and pollinator groups, some authors refer to color through visual attributes defined by human perception, such as brightness, saturation, and hue (Smith, 2014;Reverté et al, 2016). Whilst the use of these attributes has provided interestingly insights into the distribution of plant colors along spatial gradients (Gray et al, 2018), and its association with biotic and abiotic factors (Dalrymple et al, 2015(Dalrymple et al, , 2020Reverté et al, 2016), it is still unclear if color attributes applicable to human vision are universal among animals and relevant for all species. Brightness, for example, is a confound to color perception (Kelber et al, 2003) and in primates during the early stages of visual processing the chromatic and achromatic information are separated (Livingstone and Hubel, 1988;Nassi and Callaway, 2009) into the magnocellular and pavocellular pathways.…”

Fragmentary Blue: Resolving the Rarity Paradox in Flower Colors

“…However, few studies have considered pollinator perception in such analyses, and below we attempt to synthesize available evidence to bridge the potentially contributing abiotic and biotic factors that might influence flower coloration. In this regard, recent work evaluating potential abiotic or biotic factors for the Australian continent reveals that both may be important, but biotic factors modeled with appropriate bee pollinator color space appear to be the main evolutionary driver of flower coloration (Dalrymple et al, 2020).…”

“…In addition, other factors can also be at play, as recent evidence suggests that increased pollinator competition may also promote convergence toward the most preferred colors (Shrestha et al, 2019a;Tai et al, 2020), which is discussed in depth below. Accordingly, in harsher conditions, with less competition, higher divergence of flower colors is observed (Dalrymple et al, 2020). Surprisingly, it is not only humans for which short wavelength blue coloration has a special allure: honeybees (Morawetz et al, 2013), bumblebees (Gumbert, 2000), and stingless bees (Dyer et al, 2016a) have innate preferences for short wavelength blue colors.…”

How biotic and abiotic effects colour flowers in a land Down Under

“…In addition to pollinators as agents of selection, abiotic factors may also shape floral coloration. In this issue of New Phytologist , Dalrymple et al (2020; pp. 1972–1985) examine how common biotic and/or abiotic factors shape floral coloration in Australia.

‘An important finding of their study is that flowers tend to be more colourful in stressful growing conditions.’

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