Floral temperature patterns can function as floral guides

Abstract

Floral guides are signal patterns that lead pollinators to floral rewards after they have located the flower, and increase foraging efficiency and pollen transfer. Patterns of several floral signalling modalities, particularly colour patterns, have been identified as being able to function as floral guides. Floral temperature frequently shows patterns that can be used by bumblebees for locating and recognising the flower, but whether these temperature patterns can function as a floral guide has not been explored. Furthermore, how combined patterns (using multiple signalling modalities) affect floral guide function has only been investigated in a few modality combinations. We assessed how artificial flowers induce behaviours in bumblebees when rewards are indicated by unimodal temperature patterns, unimodal colour patterns or multimodal combinations of these. Bees visiting flowers with unimodal temperature patterns showed an increased probability of finding rewards and increased learning of reward location, compared to bees visiting flowers without patterns. However, flowers with contrasting unimodal colour patterns showed further guide-related behavioural changes in addition to these, such as reduced reward search times and attraction to the rewarding feeder without learning. This shows that temperature patterns alone can function as a floral guide, but with reduced efficiency. When temperature patterns were added to colour patterns, bees showed similar improvements in learning reward location and reducing their number of failed visits in addition to the responses seen to colour patterns. This demonstrates that temperature pattern guides can have beneficial effects on flower handling both when alone or alongside colour patterns.

Keywords: Floral displays; Floral guides; Multimodality; Plant-pollinator evolution; Pollination; Temperature patterns.

Fig. 1

The colour and temperature patterns applied across artificial flower variants. a A test flower with no colour patterns and no control panels, as used in Plain Control, Unimodal Warm and Hot artificial flower variants. b A test flower with a blue colour panel, in front of the rewarding feeder, as used in test groups Unimodal and Multimodal Blue flower variants. c A test flower with a pink colour panel, in front of the rewarding feeder, as used in test groups Unimodal and Multimodal Pink flower variants. d A test flower with no colour pattern but with control panels, as used in the group ‘Panels Control’ flower variant. Note that the control panels are barely visible, but are present in front of all of the blue feeder tunnels in panels b–d. e–f Thermal images showing the heating that occurs when the ‘Hot’ (c) and ‘Warm’ (f) guide heating elements are turned on. The temperature scale in panels e and f is given in the colour scale to the right of each panel in °C. Note that both thermal images have the same temperature scale to allow comparison of the spread and amount of heating each thermal pattern generates

Fig. 2

The relationships between each handling metric and experience (focal visit number) across bees that foraged on different artificial flower variants, different test groups. a The mean proportions of failed visits (proportions are calculated for the previous ten focal visits at ten, twenty and thirty focal flower visits) for bees in each test group. Error bars indicate ± one standard error of the mean. b A summary of the best fitting model for proportions of failed visits for bees foraging across all flower test groups. Points plotted are the mean proportions of failed visits for bees presented with different pattern or pattern combinations, as predicted by the best fitting model. Error bars indicate ± one standard error of the model mean estimates. c The mean proportion of first-feeder visits for bees in each test group. Error bars indicate ± one standard error of the mean. d A summary of the best fitting model for proportions of first-feeder visits for bees foraging across all flower test groups. Points plotted are the mean proportions of first-feeder visits for bees presented with different pattern or pattern combinations, as predicted by the best fitting model. Error bars indicate ± one standard error of the model mean estimates. e Solid lines indicate the mean reward search times for bees in each test group as predicted by the best fitting search time model. Dashed lines indicate ± one standard error of the model mean estimates. f A summary of the best fitting model for reward search times of bees foraging across all flower test groups. Solid lines indicate the mean reward search times for bees presented with different patterns or combinations of patterns, as predicted by the best fitting model. Dashed lines indicate ± one standard error of the model mean estimates. Across panels b, d and f, colours and labels indicate the patterns presented to bees: ‘blue + warm’ and purple colour, bees presented with both Warm temperature and Blue colour patterns together; ‘blue’ and blue colour, indicates bees presented with blue colour patterns; ‘warm’ and orange colour, bees presented with warm temperature patterns; ‘hot’ and red colour, bees presented with Hot temperature patterns; ‘base’ and black colour, bees not presented with patterns (control groups) or patterns not indicated by any other line, thus ‘base’ includes bees whose responses were indistinguishable from control bees