Bees rewarded by instinctive and learned behaviours

From the instant that a newly hatched turtle begins heading toward the sea to the irresistible urge that salmon have to return to the stream of their birth, many animal behaviours are driven by hard-wired instincts that are impossible to resist. However, animals are also capable of learning a wide range of activities, and it is the similarities and differences between the mechanisms that underlie these two types of behaviour – instinctive and learned – that intrigues Gene Robinson, from the University of Illinois at Urbana-Champaign, USA. ‘Little is known about the degree to which related instinctive and learned behaviours rely upon similar molecular mechanisms’, says Robinson, who wanted to investigate the expression patterns of genes in the brains of honey bees embarking on instinctive searches for mates and those that have learned to forage for food to find out how they compare.

Knowing that male drones at the bee research facility in Urbana favour searching for mates in the afternoon, Robinson and Nicholas Naeger trained female foragers to seek out food at a nearby feeder at the same time of day. The duo then collected the brains of bees from both groups when on the verge of embarking on their afternoon flights and compared the gene expression patterns with those in the brains of bees collected the following morning.

Focusing on one region of the brain – the mushroom body – that is known to participate in learning and memory, Robinson and Naeger began analysing the differences in the gene expression patterns. Not surprisingly, a large number of the differences in gene expression – 5680 – were due to the sex difference between the male drones and the female workers. However, after filtering those differences out, the team identified 623 specific expression changes in genes associated with the drones’ instinctive mating flight behaviour, in contrast with the 473 gene expression changes that the duo found in the female workers that had learned to forage. And when Naeger and Robinson compared the gene expression patterns of both castes of bee just before initiating their flights with those of inactive bees the following morning, they identified 166 genes that were critical for both flight behaviours.

Classifying the genes that were common to both types of flight, the duo identified members of the family of ‘unfolded protein binders’ and heat shock proteins, which are usually expressed in response to stressful situations. In addition, genes that are involved in reward-conveying dopamine neurotransmission also contributed to both flight behaviours, and the duo comments, ‘The similarities suggest that reward-related instinctive and learned behaviours share common molecular architecture’.

However, the drones that were embarking on instinctive mating flights seemed to have primed transcription factors that would prepare the brain for navigational learning. Meanwhile, the foraging females that had already learned their flight path were modifying the expression of genes that contribute to brain remodelling and protein modification, which contribute to memory formation.

Pointing out that this is only the second study that has investigated similarities and differences between instinctive and learned behaviours, Naeger and Robinson say that these studies ‘show that there are common molecular substrates for both instinctive and learned behaviours’. Having identified that genes that contribute to reward (dopaminergic) sensations are activated in the altruistic behaviours of foragers gathering food on behalf of the entire colony, they also say, ‘These findings suggest that social evolution has relied on elements of reward processing, involving both innate and learned behaviours, which function at the level of the individual in order to build a social reward system’.