1. Many insular plant species inhabiting different archipelagos worldwide present typical ornithophilous floral traits (e.g., copious nectar, red-orange colours), but most of them are visited by insectivorous/granivorous birds and lizards, which act as generalist pollinators. Oceanic islands promote these ecological interactions mainly due to the scarcity of arthropods. Our goal is to understand how these generalist interactions contribute to the shift of floral traits from entomophily (mainland) to ornithophily or saurophily (island), where specialist nectar-feeding birds have not inhabited. 2. We used the well-known pollination interactions occurring in the Canary Islands to evaluate two proposed ecological hypotheses, bee-avoidance or bird-attraction, explaining evolutionary transitions of floral traits. Specifically, we studied the flower colour conspicuousness of bird-pollinated Canarian species visited by birds and lizards with their closest relatives from the mainland mainly visited by bees. We analysed the chromatic contrast of flower colours using visual models of bees, birds, and lizards and the achromatic contrast in visual models of bees. We also compared reflectance spectra marker points of flowers with available spectral discrimination sensitivities of bees and birds. 3. Using a phylogenetically corrected framework of independent plant lineages, our results revealed that bird-pollinated Canarian species showed lower chromatic contrast according to bees and lizard visual models than their mainland relatives, but similar chromatic contrast for bird vision. In addition, reflectance spectra marker points of the Canarian species were displaced to the longest wavelengths, far from the wavelengths of maximum discrimination of bees, but close to birds. 4. We conclude that the avoidance of bees would be a primary ecological strategy explaining the evolutionary transitions of flower colours from melittophily to ornithophily. The lower conspicuousness of bird-pollinated Canarian flowers in lizards is perhaps a side effect of the bee-avoidance strategy rather than an independent evolutionary strategy. Together, these findings provide insights into how vertebrate generalist pollinators can also lead to divergence of floral traits in insular habitats, but also in other arthropod-poor habitats.

1. Description of methods used for collection/generation of data: The flower reflectance spectra were made with USB-2000 and Jaz A1465 Ocean Optics spectrophotometers (Duiven, The Netherlands) equipped with a top sensor system deuterium-halogen standardized light source, DT-MINI-GS-2 and DH-2000 lamps, respectively, and a coaxial fibber cable (QR-400-7-UV-VIS-BX; Ocean Optics). Reflectance corresponds to the proportion of a standard white reference tile (WS-1-SS; Ocean Optics). For all measurements, we kept the distance between the petals and the measuring probe constant and with an angle of illumination and reflection fixed at 45°. Spectra data were processed with OceanView software (version 2.0.8; Ocean Optics) and calculated in 5-nm wide spectral intervals in the range of 300–700 nm. 2. Methods for processing the data: We used the ‘getspec’ function of the ‘pavo’ R-package to load the colour spectral data between 300 and 700 nm of each flower. To reduce noise, the data was smoothed with a span of 0.25 and negative values were corrected by setting the minimum value to zero and scaling other values accordingly (‘procspec’ function). 3. Instrument- or software-specific information needed to interpret/reproduce the data, please indicate their location: USB-2000 and Jaz A1465 Ocean Optics spectrophotometers (Duiven, The Netherlands) equipped with a top sensor system deuterium-halogen standardized light source, DT-MINI-GS-2 and DH-2000 lamps, respectively, and a coaxial fibber cable (QR-400-7-UV-VIS-BX; Ocean Optics). Reflectance corresponds to the proportion of a standard white reference tile (WS-1-SS; Ocean Optics). Spectra data were processed with OceanView software (version 2.0.8; Ocean Optics). 4. Standards and calibration information, if appropriate: Reflectance corresponds to the proportion of a standard white reference tile (WS-1-SS; Ocean Optics).

Fundación CajaCanarias/La Caixa (2022CLISA29), Spanish Ministry of Science and Innovation (PID2020-116222GB-100).

Flower reflectance data

Peer reviewed