A species of tropical butterfly with unusually expanded brain structures shows a fascinating mosaic pattern of neuronal expansion linked to a cognitive innovation.
The study, published today in Current biologyinvestigates the neural foundations of behavioral innovation in heliconium butterflies, the only genus known to feed on both nectar and pollen. As part of this behavior, they demonstrate a remarkable ability to learn and remember spatial information about their food sources, abilities previously connected to the expansion of a brain structure called mushroom bodies, responsible for learning and memory.
Lead author Dr Max Farnworth, from the School of Biological Sciences at the University of Bristol, explained: “There is great interest in how larger brains may support greater cognition, behavioral precision or flexibility. But during brain expansion brain, it is often difficult to disentangle the effects of increases in overall ability. size due to changes in internal structure.”
To answer this question, the study authors delved into the changes that occurred in the neural circuits that support learning and memory in heliconium butterflies. Neural circuits are quite similar to electrical circuits, since each cell has specific targets with which it connects and forms a network with its connections. This network then triggers specific functions by building a circuit.
Through detailed analysis of the butterfly brain, the team discovered that certain groups of cells, known as Kenyon cells, expanded at different rates. This variation led to a pattern called mosaic brain evolution, where some parts of the brain expand while others remain unchanged, analogous to mosaics, all being very different from each other.
Dr Farnworth explained: “We predict that because we see these mosaic patterns of neural changes, these will be related to specific changes in behavioral performance, in line with the range of learning experiments showing that heliconium “They outperform their closest relatives only in very specific contexts, such as long-term visual memory and pattern learning.”
To feed on pollen, Heliconius butterflies need to have efficient foraging routes, as pollen plants are quite rare.
Project supervisor and co-author Dr Stephen Montgomery said: “Rather than having a random route to forage, these butterflies apparently choose fixed routes among floral resources, similar to a bus route. The planning and The memory required for this behavior is fulfilled by the ensembles of neurons within the mushroom bodies, hence we are fascinated by the internal circuits. Our results suggest that specific aspects of these circuits have been modified to achieve enhanced capabilities. heliconium butterflies.”
This study contributes to the understanding of how neural circuits change to reflect innovation and cognitive change. Examining neural circuits in tractable model systems, such as insects, promises to reveal genetic and cellular mechanisms common to all neural circuits, thus potentially closing the gap, at least at the mechanistic level, with other organisms such as humans.
Looking ahead, the team plans to explore neural circuits beyond the learning and memory centers of the butterfly brain. They also aim to increase the resolution of their brain mapping to visualize how individual neurons are connected at an even more granular level.
Dr Farnworth said: “I was very fascinated by the fact that we see such high degrees of conservation in brain anatomy and evolution, but then very prominent but distinct changes.”
“This is a really fascinating and beautiful example of a layer of biodiversity that we don’t normally see, the diversity of the brain and sensory systems, and the ways in which animals process and use information provided by the environment around them,” he concluded. Dr. Montgomery.