Bees use invisible heat patterns to choose flowers

beeIn the hidden world of flower-pollinator interactions, heat can act not only as life-sustaining warmth, but can also be part of the rich variety of sensory signposts that flowers use to provide advertisement and information for their insect pollinators.

The majority of flowers examined, including many common in gardens, such as poppies and daisies, had complex patterns of heat across their petals, echoing the colourful patterns that we see with our own eyes.

On average these patterns were 4–5°C warmer than the rest of the flower, although the patterns could be as much as 11°C warmer.

We made artificial flowers that copied these heat patterns, but did not include the corresponding colour patterns.

While these artificial flowers look identical to human eyes, and we are not able to tell them apart, it is a different case for foraging bumblebees.

Bumblebees, who visit a wide range of different flowers, were found to be able to use these patterns to distinguish between different flowers and the rewards that they provide.

The study’s lead author, Dr Heather Whitney, from the University of Bristol’s School of Biological Sciences, said: “The presence of multiple cues on flowers is known to enhance the ability of bees to forage efficiently, so maximising the amount of food they can take back to sustain the rest of their colony.

“Climate change might have additional previously unexpected impacts on bee-flower interactions by disrupting these hidden heat patterns.”

The lead author of this publication, Mike Harrap, is a NERC-funded PhD student based at the University of Bristol. Heather Whitney was funded by the European Research Council.

(edited version of University of Bristol press release)

FURTHER READING

Harrap MJM, Rands SA, Hempel de Ibarra N & Whitney HM (2017). The diversity of floral temperature patterns, and their use by pollinators. eLife 6: e31262 | full text (open access) | dryad dataset | accompanying insight article by Bing & Kessler

Advertisements

arom’in around the flowers: how bees cope with a smelly environment

beeguest blog by David Lawson

Sensory overload happens to us all. Whether you’re in the centre of town or waiting for a train at a station, sometimes you’re bombarded by a cacophony of noises, images and even smells. Your mind can only do so much to sort out what’s relevant to you or what’s worth ignoring. People talking, music booming, buses passing, announcements blaring out into the air. You hear a phone ring and assume it’s someone else’s, but then you notice the vibrating of the phone in your pocket and know it’s yours. By matching up the ringing of the phone with the vibration, you’re certain that this information is relevant to you.

The environment of a foraging bee can be equally noisy, but not just with sound. These complex floral marketplaces are filled with the smells and colours of various flowers, some of which are more rewarding than others, but just like us and our phones, bees have a similar techniques to find the relevant flowers. In our recent publication in Royal Society Open Science, we have looked into the ways in which bumblebees find flowers while looking for nectar. Using artificial flowers, we recorded how quickly the bees can learn the difference between scented flowers when exposed to environments filled with different scents. We discovered that bees could differentiate between the flowers much faster when the flowers had visual aspects along with their scents.

These findings suggest that the visual aspects of flowers could be used as a backup for the scent of flowers when scent is compromised, ensuring that bees can find the most rewarding flowers in uncertain environments. This helps us understand how bees, and the pollination services they provide, might be affected in a rapidly changing world.

Further reading

Lawson DA, Whitney HM & Rands SA (2017). Colour as a backup for scent in the presence of olfactory noise: testing the efficacy backup hypothesis using bumblebees (Bombus terrestris). Royal Society Open Science 4: 170996 | full text (freely readable open access) | pdf

Bumblebees can tell each other apart using scent marks

We have discovered that bumblebees have the ability to use ‘smelly footprints’ to make the distinction between their own scent, the scent of a relative and the scent of a stranger.

beeBumblebees have the ability to use ‘smelly footprints’ to make the distinction between their own scent, the scent of a relative and the scent of a stranger. By using this ability, bees can improve their success at finding good sources of food and avoid flowers that have already been visited and mined of nutrients by recognising who has been there previously. A study conducted as part of Richard Pearce‘s PhD that shows this has been published in Scientific Reports today.

Bumblebees secrete a substance whenever they touch their feet to a surface, much like us leaving fingerprints on whatever we touch. Marks of this invisible substance can be detected by themselves and other bumblebees, and are referred to as scent marks.

We performed three separate experiments with bumblebees, where they were repeatedly exposed to rewarding and unrewarding flowers simultaneously that had footprints from different bees attached to them.

Each flower type either carried scent-marks from bumblebees of differing relatedness (either their own marks, sisters from their nest, or strangers from another nest), or were unmarked.

We discovered that bees were able to distinguish between these four different flower types, showing that not only can bees tell the marks of their own nest mates from strangers, but also that they can discriminate between the smell of their own footprints and those of their nest mate sisters.

This is the first time it has been shown that bumblebees can tell the difference between their scent and the scent of their family members. This ability could help them to remember which flowers they have visited recently.

Bumblebees are flexible learners and, as we have discovered, can detect whether or not it is they or a different bumblebee that has visited a flower recently. These impressive abilities allows them to be more clever in their search for food, which will help them to be more successful.

This work, published today in Scientific Reports, was funded by the EPSRC, through the Bristol Centre for Complexity Science. This blog posting is an edited version of the University of Bristol press release.

further reading

Pearce RF, Giuggioli L & Rands SA (2017). Bumblebees can discriminate between scent-marks deposited by conspecifics. Scientific Reports 7: 43872 | full text

Pollinator movement through fragmented landscapes

beeMany pollinators live in complex and changeable environments. The location of of their food sources changes with time of year (as plants flower), time of day (as flowers open and close or nectar flows) and physical location (for although plants may not move very much during a flowering season, the places that flowers may be found may differ dramatically with time). Natural selection has shaped the behaviours of pollinators so that they have a suite of behaviours that allow them to exploit their environment: although it is unlikely that they know exactly when and where food will be available, they are able to couple clues from the environment with a repertoire of behaviours that will allow them to find food.

Agriculture and other human-generated change is altering the enviroment that pollinators live within, and it is very likely that the rules they are following are not ideal for the changed landscape. Because pollinators are essential for crop production, agricultural policies often dictate that there is some concession to the pollinators. This could be through leaving set-aside ‘wild’ land for nests and wild flowers, or by adding corridors of uncropped land or hedgerows where beneficial species can travel between environments. However, the pollinators will still be following their evolved rule sets, which means that we need to consider whether our concessions to them are of any use. This is something that is difficult to measure, and we need to use a wide range of techniques to ask whether particular manipulations are of benefit to some or many helpful species.

As a behavioural ecologist, I’m interested in how the behavioural decisions made by individual animals allow them to interact with the environment. For most animals, the environment that they live in is highly complex and frequently unpredictable, and it is often a challenge for us to understand how a particular decision gives the animal an advantage over an alternative behaviour. As well as conducting experiments and making observations of behaviour, we can also use theoretical techniques for exploring how simple behaviours could be the best solutions for dealing with complex environments. Simulation techniques are particularly useful for understanding how particular sets of decision allow an animal to cope with changes at the landscape level (bringing together two very different disciplines: landscape ecology and behavioural ecology).

In a paper that has just been published in PeerJ (Rands 2014), I describe a series of models describe a framework for considering how landscape alterations affect the foraging success of a pollinator nesting within the environment. These models build on earlier ideas presented by Rands and Whitney (2010, 2012, discussed in an earlier blog entry), where we simulated landscapes with simple geometries and allowed pollinators to forage within them. In the new PeerJ paper, I describe how hedgerow removal and set-aside field creation may affect the movement of pollinators. The models demonstrate that decreasing either landscape connectivity (be removing hedges) or wild land availability (through having lots of fields of unusable crops) affect how often pollinators have to switch between different environmental types. This may be important for how they find and collect food: for example, swapping between habitats may lead to a temporary reduction in nectar uptake if the pollinator has to work out how to collect it from a newly-encountered shape of flower.

The models are a first step, and are presented as a means of discussing how we can manipulate the environment in a reproducible way within a model. What needs to be done now is to identify a suitable set of behavioural rules to follow (for those presented in the models are basic, and are very likely to be improved upon!). Ongoing work should be able to demonstrate whether particular environmental manipulations are of value to some of our threatened pollinator species.

Further reading

Rands SA (2014). Landscape fragmentation and pollinator movement within agricultural environments: a modelling framework for exploring foraging and movement ecology. PeerJ 2: e269 | full text | pdf

Rands SA & Whitney HM (2010). Effects of pollinator density-dependent preferences on field margin pollination in the midst of agricultural monocultures: a modelling approach. Ecological Modelling 221: 1310-1316 | abstract | pdf (postprint version)

Rands SA & Whitney HM (2011). Field margins, foraging distances and their impacts on nesting pollinator success. PLoS One 6: e25971 | full text | pdf

How do pollinators respond to the shape of agricultural landscapes?

beeThe global debate rumbles on about pollinator decline. In the UK, the recent European Commission directive banning neonicotinoid pesticides has at least partly been a catalyst for some very public debate on why decline is happening, and what could be done about it (with the BBC rushing out a nicely-balanced edition of their science programme Horizon, exploring a few of the factors that may be driving the disappearance of pollinators).

This posting ties in with my talk at INTECOL 2013 in London (if you’re there, it’s in the Ecosystem Services session in Capital Suite 13 on Wednesday 21st at 2.15pm).

Aside from disease and poisoning, one factor that is frequently pointed to is the huge changes that have been made to the landscape in recent years.  The intensification of agriculture has meant that the ‘wild’ bits of the landscape have been taken away through changes in field management, and the steady creep of urbanisation.  These wild bits, even if they’re simply hedgerows and the other untidy bits at the edges of fields, are hugely important for providing nesting sites, refuge and food for wild pollinators and the other beasties that contribute to making agricultural systems work.  If we take these messy little spaces away, not only do we remove the resources that these beneficial species use, but we also make it much more difficult for those existing beneficial species already present to gain access to the parts of our managed agricultural species that are not close to these refuge areas.

Working with Heather Whitney (University of Bristol), I’ve done some work looking at how the shape of the agricultural environment affects the ability of pollinators to access it. In a paper published in Ecological Modelling, we considered a simple case where the environment was considered to be a square grid of hedgerows, with pollinators nesting in the hedgerows. The pollinators were considered to only fly a set distance from their nest (realistic, since many solitary bees fly a maximum  of about a kilometre from their nest), and the model demonstrated that if this distance was small, and kind of environmental manipulation that increased the size of fields beyond a certain point may have a detrimental effect upon the amount of wild space available to a pollinator.

However, the model was extremely simplistic.  Although I believe very strongly in keeping exploratory models as simple as possible, it felt like there was too many rigid assumptions made when we assumed that the landscape was a square grid.  In order to make the landscapes more realistic, we took two approaches: firstly, simulating random landscapes filled with hedgerows, and secondly, using landscape data from the UK, where there is a large amount of variation in wild refuge space within the landscape, as you can see from the four sample landscapes given below.

Examples of British field structures used within the model
Examples of British field structures used within the model

These landscape-informed models, published in PLoS One, demonstrated again that pollinators that only fly short distances from their nest (less than about 125 metres, which is relevant for some solitary bees such as Andrena hattorfiana) are affected heavily by landscape manipulations, but are unlikely to benefit from having wild land added to the environment unless it is targetted specifically for them (the equivalent of trying to help an isolated island community by building a new hospital for them on the mainland.  For species travelling more than 125 metres, adding wild space into the (British) landscape is a good thing, regardless of the exact distance the species travels.

So, we should maybe consider how far specific pollinators are able to travel when we are considering their conservation.  Lots of work is being conducted by  research groups across the world to quantify and observe the lengths of these commuting distances, and many research teams are finding that pollinators are thriving in response to many unexpected resources such as urban gardens. We still have a lot of work to do to explore how different species choose to move through the environment, and how this can be manipulated to benefit them and us.

Further reading

Rands SA & Whitney HM (2010). Effects of pollinator density-dependent preferences on field margin pollination in the midst of agricultural monocultures: a modelling approach. Ecological Modelling 221: 1310-1316 | abstract | pdf (postprint version)

Rands SA & Whitney HM (2011). Field margins, foraging distances and their impacts on nesting pollinator success. PLoS One 6: e25971 | full text | pdf