Abstract
Flower color has been studied in different ecological levels of organization, from individuals to communities. However, it is unclear how color is structured at the intrafloral level. In bee-pollinated flowers, the unidirectional gradient in color purity and pollen mimicry are two common processes to explain intrafloral color patterns. Considering that floral traits are often integrated, usually reflecting evolutionary modules under pollinator-mediated selection, we hypothesize that such intrafloral color patterns are structured by intrafloral color modules as perceived by bee color vision system. Here, we studied the tropical bee-pollinated orchid Cattleya walkeriana, given its intrafloral color complexity and variation among individuals. Considering bee color vision, we investigated if intrafloral color modules arose among intrafloral patches (tip or base of the sepals, petals, and labellum). We expected a separate color module between the labellum patches (the main attractive structure in orchids) and petals and sepals. We measured the color reflectance and calculated the photoreceptor excitation, spectral purity, hue, and the chromatic contrast of the floral structures in the hexagon color model. Spectral purity (saturation) was higher in the labellum tip in comparison to petals and sepals, generating a unidirectional gradient. Labellum base presented a less saturated yellow UV-absorbing color, which may reflect a pollen mimicry strategy. C. walkeriana presented three intrafloral color modules corresponding to the color of petals and sepals, the color of the labellum tip, and the color of labellum base. These color modules were unrelated to the development of floral structures. Given the importance of intrafloral color patterns in bee attraction and guidance, our results suggest that intrafloral patterns could be the outcome of evolutionary color modularization under pollinator-mediated selection.
Highlights
Floral color is one of the most important signals in plant-pollinator communication, usually increasing pollinators efficiency in detecting flowers in nature and improving their efficacy in obtaining floral resources and pollinate the flower (Wester and Lunau, 2017)
We investigated the intrafloral color patterns of the tropical bee-pollinated orchid Cattleya walkeriana Gardner focusing on interindividual variation of hue and spectral purity taking into account the bee-color vision system
The loci of sepals and petals were in the blue section of the hexagon, while labellum tip loci fell in the UV-blue section and labellum base loci were in blue-green section (Supplementary Figure S2)
Summary
Floral color is one of the most important signals in plant-pollinator communication, usually increasing pollinators efficiency in detecting flowers in nature and improving their efficacy in obtaining floral resources and pollinate the flower (Wester and Lunau, 2017). Plants will adapt to the perception of pollinators, and pollinators will adapt to floral signals These processes can generate floral color patterns structured on different ecological organization levels, from communities (Shrestha et al, 2014; Bergamo et al, 2018; Camargo et al, 2019), populations (Mascó et al, 2004; Newman et al, 2012), to the inter-individual level within a population, i.e., color polymorphisms (Bergamo et al, 2016; Jiménez-López et al, 2019; Aguiar et al, 2020). Intrafloral color patterns are especially common in bee-pollinated flowers (Camargo et al, 2019), and are important features favoring legitimate visits (Medel et al, 2003; Leonard and Papaj, 2011; Papiorek et al, 2016)
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