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Christie Wilcox
Caffeine has been a part of human cultural heritage for more than
five thousand years. From ancient teas and coffees to todays energy
drink craze, you could say that as a species, we’re hooked. But we’re
not the only ones — a new study published in Science today has found
that pollinators get a daily buzz off caffeine, too, and it keeps them
coming back for more.
It was originally thought that plants
produced caffeine as a pesticide, which is, in part, true. Caffeine in
leaves and seeds can paralyze and kill some insects that feed on plant
parts, preventing damage. Some plants, like
Coffea arabica or
Mountain Coffee, also release caffeine into the soil around them that
inhibits the growth of other seeds, thus giving their seedlings a
competitive advantage. For the past few decades, these were thought to
be the uses of caffeine to plants: keep insects away, enhance seedling
survival. Yet, scientists have found low levels of caffeine in plant
nectars, which seems a puzzling place for an insecticide. Caffeine has a
bitter taste, so not only is it dangerous to produce in nectar because
it might harm the pollinators the plant relies on, it could simply deter
them. After all, bees are adept at
detecting and avoiding toxins.
Yet the team, led by Dr Geraldine Wright from Newcastle University,
found that citrus and coffee plants produced low levels of caffeine in
their nectar — almost as much caffeine as a cup of instant coffee. What
benefits, they wondered, could this caffeine be providing?
In humans, caffeine is a central nervous system stimulant, making us
feel more alert and awake. Some early studies suggested that it also
improves short and long term memory, but findings have been
inconsistent. Most importantly, though, low doses of caffeine activate
the reward system in our brains, contributing to its addictive nature.
So, the team wondered if the same was true for bees.
They trained bees to associate a floral scent with tasty sugar
solutions dosed with different amounts of caffeine. Even low doses of
caffeine had a profound effect on the bees’ long tem memory: when given
nectar-levels of caffeine, three times as many bees remembered the
conditioned scent a day later and responded to it as if expecting their
sugary reward, and twice as many still remembered three days later.
But to really understand why, the scientists examined honeybee
brains. They found that doses of caffeine primed neurons in the bees’
brains associated with learning and memory formation, making it easier
for them to fire. The overall result is that the bees are able to pair
scent with location faster and more easily. The caffeine boosts their
memory-making ability.
The scientists believe that the low levels of caffeine found in
citrus and coffee nectars have an important ecological role, providing
pollinators with a jolt that helps them remember where a plant is and
return more often. “Remembering floral traits is difficult for bees to
perform at a fast pace as they fly from flower to flower” explains Dr.
Wright. But, the scientist found, caffeine-spiked nectars enhance the
bees’ memory. “Our experiments suggest that by affecting a pollinator’s
memory, plants reap the reproductive benefits arising from enhanced
pollinator fidelity,” conclude the authors. The enhanced memory is a win
for the bees, too. “Caffeine in nectar is likely to improve the bee’s
foraging prowess” says Dr. Wright.
Today, honeybees are in decline worldwide, losses which are being
felt strongly by the agricultural industry. This study gives us a better
understanding of how bees find and choose plants to pollinate, which
may prove vital information for farmers. Planting species like coffee
and citrus amongst crops might improve pollination, or, genetic
modification might be able to help make crops that bees prefer. The more
we know about bee foraging, the better a chance we have at keeping them
around and healthy, both for their sake and ours.
Studies like this one not only teach us more about bee brains — they
also shed light on our own. While human brains are significantly more
complex than those of pollinating insects, there are many similarities.
As co-author Dr. Julie Mustard explains, “Although human and honeybee
brains obviously have lots of differences, when you look at the level of
cells, proteins and genes, human and bee brains function very
similarly. Thus, we can use the honeybee to investigate how caffeine
affects our own brains and behaviors.” “What we see in bees could
explain why people prefer to drink coffee when studying,” added Dr.
Wright.
Citation:
Wright G.A. et al. (2013). Caffeine in Floral Nectar Enhances a Pollinator’s Memory of Reward, Science
