Multiple origins of lipid‐based structural colors contribute to a gradient of fruit colors in Viburnum (Adoxaceae)

Abstract

Summary Structural color is poorly known in plants relative to animals. In fruits, only a handful of cases have been described, including in Viburnum tinus where the blue color results from a disordered multilayered reflector made of lipid droplets. Here, we examine the broader evolutionary context of fruit structural color across the genus Viburnum. We obtained fresh and herbarium fruit material from 30 Viburnum species spanning the phylogeny and used transmission electron microscopy, optical simulations, and ancestral state reconstruction to identify the presence/absence of photonic structures in each species, understand the mechanism producing structural color in newly identified species, relate the development of cell wall structure to reflectance in Viburnum dentatum, and describe the evolution of cell wall architecture across Viburnum. We identify at least two (possibly three) origins of blue fruit color in Viburnum in species which produce large photonic structures made of lipid droplets embedded in the cell wall and which reflect blue light. Examining the full spectrum of mechanisms producing color in pl, including structural color as well as pigments, will yield further insights into the diversity, ecology, and evolution of fruit color.

Self-assembled, disordered structural color from fruit wax bloom

“…The dissolved epicuticular wax is transparent in (chloroform) solution over the visible range. Spectrophotometry shows a strong absorption in UV below 300 nm for blueberry wax, absent in other (11), Elaeocarpus angustifolia (12), Pollia species (13,14), Margaritaria nobilis (15), Viburnum species (16,17), and Lantana strigocamara (18). species (fig.…”

“…A handful of other known blue fruits have been identified as structurally colored (see Fig. 1) (11)(12)(13)(14)(15)(16)(17)(18).…”

“…( E ) Confirmed occurrence of bloom disseminules across phylogeny. Previously known structurally colored (multilayer) fruits are shown in dark blue: Delarbrea michieana ( 11 ), Elaeocarpus angustifolia ( 12 ), Pollia species ( 13 , 14 ), Margaritaria nobilis ( 15 ), Viburnum species ( 16 , 17 ), and Lantana strigocamara ( 18 ).…”

Evidence of fruit syndromes in the recently diverged wild tomato clade opens new possibilities for the study of fleshy fruit evolution

“…Research across many species has established that fruit traits do not vary independently. Instead, certain suites of traits tend to occur together (for example small size, bright colors, and high sugar content) and often involve correlations between external appearance and internal chemical composition (Nevo et al, 2019; Schaefer et al, 2014; Sinnott‐Armstrong et al, 2020; Sinnott‐Armstrong et al, 2023; Valido et al, 2011). Repeatedly observed associations of certain traits are often referred to as fruit or dispersal syndromes (Rojas et al, 2022; Valenta & Nevo, 2020; van der Pijl, 1969).…”

“…Instead, certain suites of traits tend to occur together (for example small size, bright colors, and high sugar content) and often involve correlations between external appearance and internal chemical composition Schaefer et al, 2014;Sinnott-Armstrong et al, 2020;Sinnott-Armstrong et al, 2023;Valido et al, 2011).…”