According to research recently published in in the journal Science, humans aren’t the only creatures who get a good buzz from caffeine. It turns out that plants produce caffeine-laced nectar to attract honeybees and to keep the insects keep coming back for more. The psychoactive drug enables organisms rooted to the ground to influence the behavior of their moving pollinators. Not only does this new information shed light on how plants and pollinators have co-evolved, but it explains similarities in brain chemistry across the animal kingdom.
Thanks to a study by Geraldine Wright and her colleagues at Newcastle University in England, we now have little more insight on why bees are such hard workers and why they favor certain flowers. While some plants may choose to produce large amounts of nectar or blooms that resemble potential pollinator mates, others synthesize chemicals to ensure that their flying friends visit often. Wright did not set out to examine the evolutionary strategies of plants, but rather to use the honeybee as a model of investigating how certain drugs are commonly abused. Eight or nine years ago, she ran across a paper that mentioned caffeine in floral nectar, and it piqued her interest.
There are several varieties of citrus and coffee plants that produce toxic levels of caffeine in their leaves and tissues, but have low concentrations similar to that of coffee in their nectar. While the toxic levels are thought to ward off predators, the nectar may be a means of offering an incentive to pollinators. Wright conducted learning experiments with bees where she offered a treat associated with an odor. The reward consisted of either plain sugar water, or sugar water laced with caffeine. While the effect of the chemical was not obvious at first, she found that it soon produced profound changes to the insect’s memory, and that they were able to remember the smell associated with the caffeine. After 24 hours, three times as many bees remembered the odor associated with the caffeine mixture, and twice as many after 72 hours.
When they looked at the effects of caffeine on the bees’ brains, they found that it affected the sensitivity of neurons called Kenyon cells which are associated with learning and memory. The effects of caffeine on human memory remains unclear, but it raises fascinating questions on how the processes of learning have been effected by evolution over vast spans of time.