DOI: 10.5061/dryad.3n6n6
title: Data from: Flower colour and visitation rates of Costus arabicus support the "bee avoidance" hypothesis for red-reflecting hummingbird-pollinated flowers

description: Floral colour mediates plant–pollinator interactions by often signalling
 floral resources. In this sense, hummingbird-pollinated flowers are
 frequently red-coloured, and there are two tentative hypotheses to explain
 this pattern: 1. hummingbirds are attracted to red due its easier
 detection and 2. bees are sensorially excluded from red flowers. The
 second hypothesis is based on bees’ red colour blindness, which lead them
 to be less frequent and less important than hummingbirds as pollinators of
 red-reflecting flowers. Here, we untangled the role of different flower
 traits mediating plant–pollinator interactions and empirically tested the
 above hypotheses. We chose Costus arabicus due to its synchronopatric
 white- and pink-flowered individuals and its bee and hummingbird
 pollination system. Although pink flowers are not totally achromatic as
 pure red ones, they show an achromaticity degree that could drive bee
 exclusion. Specifically, we tested whether differences on red reflectance
 work attracting hummingbirds or excluding bees and the consequent
 implications for the plant's reproduction. Flower colour morphs of C.
 arabicus do differ neither in morphology nor in nectar sugar content.
 Moreover, white and pink flowers can be discriminated by the bees’ and
 hummingbirds’ colour vision system. Both groups are able to discriminate
 the red colour variation morph on the flower petals, the white flowers
 being more easily detected by bees and the pink flowers by hummingbirds.
 Bees preferentially visited the white flowers, whereas hummingbirds
 visited both colours at the same rate – both patterns corroborating the
 second hypothesis. Pollen loads deposited on stigmas did not differ
 between flower colour morphs, indicating that bees and hummingbirds play a
 similar role in the overall pollen deposition. However, bees are more
 likely to self-pollinate than hummingbirds. Self-pollination limits C.
 arabicus reproduction, and red-reflecting flowers may be better pollinated
 by discouraging bee visitation. Therefore, the intraspecific colour
 variation is driving flowers to show colour-related different levels of
 generalization. Our results support the ‘bee avoidance’ rather than the
 ‘hummingbird preference’ hypothesis. Sensory exclusion of bees seems to be
 the pressure for red-reflecting flowers evolution, driving specialization
 in hummingbird-pollinated flowers due to the costs of bee pollination on
 plant reproduction.
description: Raw reflectance of
 Costus arabicus flowersReflectance at 300-700nm
 wavelength of white and pink flowers of Costus arabicus. Reflectance of
 petals, labellum and nectar guides.reflectance.txtFlower visitation of Costus arabicusFlower visitation by bees and hummingbirds on Costus arabicus flowers. Data regarding flower colour and pollinator behaviour.visitation_data.txtPollinator movement behaviour on Costus arabicusBees and hummingbirds movement between Costus arabicus individuals while foraging on flowerspollinator_movement.txtTraits of Costus arabicus white and pink flowersData regarding morphology, nectar traits, pollen deposition and colour in relation to the bee and hummingbird vision of Costus arabicus flowersflower_attributes.txtBee and hummingbird discrimination between Costus arabicus flowersEach data refers to the discrimination between a par of white and pink flower colour morphs to the bee and hummingbird vision. Data for petals, labellum and nectar guides.discrimination.txt