1. Ecology
  2. Plant Biology
Download icon

Pollination: Solar flower power

  1. Julia Bing
  2. Danny Kessler  Is a corresponding author
  1. Max Planck Institute for Chemical Ecology, Germany
Insight
  • Cited 0
  • Views 1,783
  • Annotations
Cite this article as: eLife 2017;6:e33591 doi: 10.7554/eLife.33591

Abstract

Bumblebees use invisible temperature patterns on flowers to make foraging decisions.

Main text

Most species of flowering plant cannot produce seeds without help from animals, like insects and birds, who transfer pollen between the flowers of different plants – often in return for a reward, such as a drink of sugar-rich nectar. In order to forage efficiently, pollinators seek out flowers with traits that they associate with a higher chance of getting a reward.

Some floral traits like color, shape and scent are obvious to our human senses, and as early as the 18th century scientists had worked out that these signals attract insects (Sprengel, 1793). However, the majority of floral traits have been discovered just recently, using modern technology. Indeed, we now know that pollinators use many different traits to find and evaluate flowers including: CO2 emission (Goyret et al., 2008); ultraviolet-absorbing pigmentation (Sheehan et al., 2016); humidity surrounding the flower (von Arx et al., 2012); fluorescence (Thorp et al., 1975); nectar color (Johnson et al., 2006); and even floral temperature (Dyer et al., 2006; Whitney et al., 2008).

Bees, for example, can use heat detectors on their legs and antennae to tell the difference between two flowers that differ in temperature by just two degrees (Heran, 1952). Now, in eLife, Sean Rands and colleagues from the Universities of Bristol and Exeter – including Michael Harrap as first author – report that bumblebees can also detect temperature differences within a single flower (Harrap et al., 2017).

Thermal images of more than 100 species of flowering plant taken in sunlight revealed a wide range of temperature patterns, reminiscent of the diversity of multi-colored petals we see with our own eyes (Figure 1A). More than half of the tested species had flowers in which some parts of the petals were at least 2°C warmer than the rest. Based on these findings, the researchers hypothesized that pollinators could use these temperature patterns to decide which flowers to visit.

Floral temperature patterns and their role in bumblebee foraging.

(A) Schematic examples of the diversity of floral temperature patterns in the sunlight. By using thermal imaging, Harrap et al. show that more than half of the species they tested have temperature differences within flowers that are big enough to be detected by bumblebees (color indicates temperature as shown in gradient). Experiments with (B) small and (C) large artificial flowers tested if bumblebees could associate a certain temperature pattern with a reward, in this case a sugar solution (blue cup symbol). Bumblebees were presented with two variants of temperature patterns, one containing the sugar reward and the other just water (top and middle rows). As a control, flowers without temperature patterns were used as both rewarding and non-rewarding flowers (bottom row). The position of the bumblebee in B and C shows which floral temperature pattern was visited the most after 60 visits, demonstrating that bumblebees were able to use these patterns to increase their foraging success.

Harrap et al. tested if bumblebees (Bombus terrestris audax) could learn to associate a reward, in this case a drop of a sugary solution, with a certain temperature pattern. They presented two types of artificial flowers containing heating elements to naïve bumblebees. The artificial flowers in the first experiment had either a warm center or a warm periphery (Figure 1B), while those in the second had warmer centers in two different shapes (Figure 1C). In all experiments, one variant contained a drop of sugar, while the other just offered water. Flowers with disconnected heating elements were used as controls.

The bumblebees did recognize different temperature patterns and, in fewer than 20 visits, had learned to forage from those flowers that would give them the reward. Importantly, when there were no temperature patterns, as is in the controls, the bumblebees could not discriminate rewarding from non-rewarding flowers. Also, once the bumblebees had learned to associate a certain temperature pattern with a sugary reward, they continued to prefer this type of flower even when the reward was removed. These results indicate that the bumblebees were using the flower temperature patterns (and not other cues) to make an informed decision when foraging.

Why did plants evolve such incredibly complex and diverse floral traits? Plants often have to compete for pollinators, either with other plant species or with other members of their own species. Any trait that enables a flower to attract more pollinators than its competitors will give it an evolutionary advantage (in other words, more seeds or higher quality offspring). Of course, plants do not invent new traits with the intention of manipulating pollinators. Instead, small mutations occur in each generation and those that change floral traits offer a chance to bring the interaction between pollinator and flower closer to perfection. Hence, it is not surprising that so many floral traits are important and act together at the same time in a single plant species.

It is exciting that sunlight is needed to turn 'on' these temperature patterns and guide pollinators to flowers. Many other floral traits are hidden from our eyes and we have just started to unveil the ways in which pollinators are able to perceive and use floral signals. Combining 'old-fashioned' natural observations with new tools, such as thermal imaging cameras or 3D printers (Campos et al., 2015), allows us to unearth the wealth of strategies that pollinators and plants use to successfully interact with each other. Floral temperature patterns triggered by sunlight to signal to bumblebees are yet another example of an impressive feat of evolution.

References

    1. Heran H
    (1952)
    Untersuchungen über den Temperatursinn der Honigbiene (Apis mellifica) unter besonderer Berücksichtigung der Wahrnehmung strahlender Wärme
    Zeitschrift Für Vergleichende Physiologie 34:179–206.
  1. Book
    1. Sprengel CK
    (1793)
    Das entdeckte Geheimniss der Natur im Bau und in der Befruchtung der Blumen
    Berlin: Vieweg.

Article and author information

Author details

  1. Julia Bing

    Julia Bing is in the Department of Molecular Ecology, Max Planck Institute for Chemical Ecology, Jena, Germany

    Competing interests
    No competing interests declared
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-9428-9172
  2. Danny Kessler

    Danny Kessler is in the Greenhouse Department, Max Planck Institute for Chemical Ecology, Jena, Germany

    For correspondence
    dkessler@ice.mpg.de
    Competing interests
    No competing interests declared
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-0410-116X

Publication history

  1. Version of Record published: December 19, 2017 (version 1)

Copyright

© 2017, Bing et al.

This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited.

Metrics

  • 1,783
    Page views
  • 166
    Downloads
  • 0
    Citations

Article citation count generated by polling the highest count across the following sources: Crossref, PubMed Central, Scopus.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Download citations (links to download the citations from this article in formats compatible with various reference manager tools)

Open citations (links to open the citations from this article in various online reference manager services)

Further reading

    1. Ecology
    2. Microbiology and Infectious Disease
    Silvia Brochet et al.
    Research Article

    Ecological processes underlying bacterial coexistence in the gut are not well understood. Here, we disentangled the effect of the host and the diet on the coexistence of four closely related Lactobacillus species colonizing the honey bee gut. We serially passaged the four species through gnotobiotic bees and in liquid cultures in the presence of either pollen (bee diet) or simple sugars. Although the four species engaged in negative interactions, they were able to stably coexist, both in vivo and in vitro. However, coexistence was only possible in the presence of pollen, and not in simple sugars, independent of the environment. Using metatranscriptomics and metabolomics, we found that the four species utilize different pollen-derived carbohydrate substrates indicating resource partitioning as the basis of coexistence. Our results show that despite longstanding host association, gut bacterial interactions can be recapitulated in vitro providing insights about bacterial coexistence when combined with in vivo experiments.

    1. Ecology
    Yutao Xiao et al.
    Research Article

    Bacillus thuringiensis (Bt) crops have been widely planted and the effects of Bt-crops on populations of the target and non-target insect pests have been well studied. However, the effects of Bt-crops exposure on microorganisms that interact with crop pests have not previously been quantified. Here, we use laboratory and field data to show that infection of Helicoverpa armigera with a densovirus (HaDV2) is associated with its enhanced growth and tolerance to Bt-cotton. Moreover, field monitoring showed a much higher incidence of cotton bollworm infection with HaDV2 in regions cultivated with Bt-cotton than in regions without it, with the rate of densovirus infection increasing with increasing use of Bt-cotton. RNA-seq suggested tolerance to both baculovirus and Cry1Ac were enhanced via the immune-related pathways. These findings suggest that exposure to Bt-crops has selected for beneficial interactions between the target pest and a mutualistic microorganism that enhances its performance on Bt-crops under field conditions.