Behavioural biology of buzz-pollinating bees and flies

Overview

More than 15,000 species of bees are capable of deploying powerful vibrations of their thorax to remove pollen from flowers with specialised morphologies. Pollination by these vibration-producing bees has given rise to the phenomenon of buzz pollination, which occurs in more than 20,000 species of flowering plants and includes important crops such as tomato, blueberries and kiwifruit. Previous work has shown that the use of vibrations to remove pollen from flowers is part of the behavioural repertoire available to some species of pollen-collecting insects, particularly bees. This project addresses two main questions (1) Why is buzz pollination is mostly restricted to a subset of bee species? (2) What determines when a bee capable of buzz pollination deploys vibrations to extract pollen from flowers?

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Image Captions

Hebridean bumblebee. (c) Mario Vallejo-Marin

Methodology

A hypothesis of why some insects do not employ vibrations to collect pollen is that they are unable to repurpose a behaviour (e.g., producing vibrations) from one context (flight, defence) to another (floral vibrations). In the first part of this project, you will investigate whether individuals that do not regularly buzz pollinate (including some bee species, flies and male bees) can learn to do vibrate flowers to access rewards. The general approach will consist on working with captive insects in a flight arena, using standard methods of experimental studies of insect cognition and behaviour.
Previous work has shown that, in buzz-pollinating bees, vibrating flowers is a last-resource when pollen cannot be obtained via other behaviours. This observation suggests that buzz-pollination is costly. In the second part of this project, you will develop a study to investigate the potential cognitive and physiological costs of buzzing flowers. For example, is there a cost in learning to use vibrations to extract pollen from flowers in terms of subsequent learning to extract other types of rewards (nectar or pollen from non-buzz-pollinated flowers)? What is the energetic cost of producing floral vibrations? You will use observation and manipulation of captive bumblebees to study the behaviour of naïve and experienced bees exposed to experimental flowers offering different types of rewards. Moreover, you will measure the energetic costs of buzzing by studying heat production and oxygen consumption in live bees buzzing flowers in flight arenas at different controlled temperatures.

Project Timeline

Year 1

Semester 1: Literature review and training on experimental approaches including designing behavioural tests and working with captive bees. Two-month residence at the University of St Andrews with co-supervisor Prof. Healy.
Semester 2: Behavioural experiment 1: Can bees that do not usually buzz-pollinate learn to deploy vibrations on flowers? Test whether male bumblebees can be conditioned to produce vibrations to access rewards.

Year 2

Semester 3-4: Behavioural experiment 2: Can other insects that do not usually buzz-pollinate learn to deploy vibrations on flowers? Test whether hoverflies can learn to vibrate to access floral rewards. Hoverflies deploy vibration behaviours in other contexts but little is known about their cognitive abilities and capacity to use novel behaviours to access rewards. Attendance to a UK-based scientific conference.

Year 3

Semester 5: Physiological experiment 1: Test the hypothesis that buzzing incurs in high physiological costs. Measure metabolic activity of buzzing bees across different temperatures.
Semester 6: Behavioural experiment 3: To what extent is buzz pollination a specialised behaviour within a bee colony? Study variation within bumblebee colonies in ability to buzz-pollinate (among female workers). Does specialisation in buzz-pollination comes at a cost in the ability to visit and extract floral rewards from other floral types? Attendance an international conference on behavioural biology.

Year 3.5

Semester 7: Design a public engagement activity to disseminate the findings of the PhD project to a broader audience. Present the activity as part of the Edinburgh Science Festival or similar event. Dissertation write-up.

Training
& Skills

Training on behavioural experiments
Development of skills on project development, experimental design, manuscript preparation and academic dissemination
Acquiring transferable skills on statistical analysis and quantitative methods
Training on biomechanics of insects and flowers
Development of public engagement activities and science communication to the public

References & further reading

Vallejo-Marin, M. (2019) Buzz pollination: studying bee vibrations on flowers. New Phytologist, 224, 1068.
Pritchard, D. J. & M. Vallejo-Marín (2020) Floral vibrations by buzz-pollinating bees achieve higher frequency, velocity and acceleration than flight and defence vibrations. The Journal of Experimental Biology, jeb.220541.
Whitehorn, P. R., C. Wallace & M. Vallejo-Marin (2017) Neonicotinoid pesticide limits improvement in buzz pollination by bumblebees. Sci Rep, 7, 15562.

Dr Mario Vallejo-Marin Lab: www.plant-evolution.org
Prof. Susan Healy Lab: https://cognitioninthewild.wp.st-andrews.ac.uk/
Dr. Gema Martin-Ordas: www.researchgate.net/profile/Gema_Martin_Ordas

Further Information
Mario Vallejo-Marin: mario.vallejo@stir.ac.uk

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