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New Paper Friday

BUMBLEBEE DOUBLE-HEADER! SOCIAL LEARNING OF STRING-PULLING AND OPTIMISM

Patricia Jones

Two cool papers came out of the Chittka lab (Queen Mary University, London) this week and I can't help but talk about both of them. First, Sylvain Alem et al.'s paper in PLOS Biology demonstrates learning and social learning of string-pulling task in the European bumblebee, Bombus terrestris. Success at string-pulling tasks are a classic method of estimating intelligence in animals (especially birds) and have been used with ravens, keas (crazy smart parrots), dogs, and many more species. One of the big debates with string-pulling is whether the animal has the insight that pulling the string will bring the reward closer, or simply moves the string accidentally, which moves the treat closer (which is in itself rewarding), so they do it again, etc. One way to test for insight is to put the treat on the end of a line with lots of slack (a "coiled string") so that as the animal pulls the string the treat does not immediately move closer, but rather it takes insight to understand that if you keep pulling the string the treat will eventually move. Alem et al. show that bees fail the coiled string task, and rather learn to pull the string through matching each tug on the string with the rewarding blue flower moving closer to them. 

Next Alem et al. showed that naïve bees learn to solve this string-pulling task from watching experienced bees do it. This reminds me of the octopus that learns how to get crab treats out of puzzle boxes by watching another octopus do it (there is a totally hokey video). This string-pulling experiment raises the exciting possibility that one bee would learn a novel way to get food (and they did have some "innovator" bees in their tests), and then that method would spread through the bee colony or even across colonies of bees foraging in the same fields. Culture! It's for the bees. (Sorry about that, I couldn't resist). 

A Bombus terrestris with an optimistic outlook. Bee by Quiet Magpie. 

A Bombus terrestris with an optimistic outlook. Bee by Quiet Magpie

The second paper came out last Friday in Science. Perry et al. examined how experience of a reward affects how bees respond to novel situations. They used a "judgement bias paradigm" that is used in research on vertebrates. In this experimental design the animal is trained to associate one stimulus (a blue color in this case) with a reward, and another stimulus (green) with no reward. The theory is that animals in a positive emotional state (i.e. happy) will respond positively to an ambiguous stimulus (a teal or turquoise color). Similarly, a negative emotional state will make animals respond negatively to ambiguous stimuli. 

Makes you wonder what happiness really is, doesn't it? When you can't ask the bee if it is happy or not, and it does not smile or sigh contently, how could we ever determine if a bee is happy? Well, one possibility is to examine how humans that currently self-describe as happy respond to all kinds of different stimuli and situations and compare that to humans that currently say they are not happy. Wright and Bower (1992) demonstrated that people in happy moods expect more positive outcomes that people that are sad. A pessimistic outlook was previously demonstrated for honeybees by Wright et al. 2011who shook the hell out of honeybees to put them in a bad mood and then showed they were pessimistic about future rewards. Who can blame them.

The recent Science paper showed that bumblebees that had been trained to associate entering a blue tube with sugar water and entering a green tube with water (no reward) were then offered the ambiguous teal/turquoise color. Bees that were fed some sugar water just before being presented with the teal color entered the teal tube faster than bees not given the sugar water. They performed control experiments to rule out that bees fed sugar first had more energy and so were just moving faster, or that they were generally more exploratory. Additionally, bees that were fed a drop of sugar water and then attacked by a robotic spider (!) started foraging again sooner than bees that were not fed a sugar water drop. So not only does a reward make bees more optimistic, it also makes them less afraid.

Dopamine is one of the human brain chemicals associated with a happy feeling. Your brain releases dopamine after you eat a cupcake, or, for that matter ingest some cocaine. When bees were given the sugar droplet but also a chemical that blocks their response to dopamine, they were afraid of the robotic spider for longer. This shows that dopamine is likely the brain chemical responsible for the optimistic behavior of these bees. 

Clearly we should all eat more cupcakes. And understand that the consumption of those cupcakes may make us irrationally unafraid of robotic spiders.