Intrafloral Color Modularity in a Bee-Pollinated Orchid

João Marcelo Robazzi Bignelli Valente Aguiar; Artur Antunes Maciel; Pamela Cristina Santana; Francismeire Jane Telles; Pedro Joaquim Bergamo; Paulo Eugênio Oliveira; Vinicius Lourenço Garcia Brito

doi:10.3389/fpls.2020.589300

Intrafloral Color Modularity in a Bee-Pollinated Orchid

Front Plant Sci. 2020 Nov 9:11:589300. doi: 10.3389/fpls.2020.589300. eCollection 2020.

Authors

João Marcelo Robazzi Bignelli Valente Aguiar¹, Artur Antunes Maciel², Pamela Cristina Santana³, Francismeire Jane Telles², Pedro Joaquim Bergamo⁴, Paulo Eugênio Oliveira⁵, Vinicius Lourenço Garcia Brito⁵

Affiliations

¹ Programa de Pós-Graduação em Entomologia, Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brazil.
² Programa de Pós-Graduação em Ecologia e Conservação dos Recursos Naturais, Instituto de Biologia, Universidade Federal de Uberlândia, Uberlândia, Brazil.
³ Programa de Pós-Graduação em Ecologia, Departamento de Ecologia, Universidade de São Paulo, São Paulo, Brazil.
⁴ Jardim Botânico do Rio de Janeiro, Rio de Janeiro, Brazil.
⁵ Instituto de Biologia, Universidade Federal de Uberlândia, Uberlândia, Brazil.

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.

Keywords: Orchidaceae; bees; color properties; color signaling; integration.