A fascinating mosaic pattern of neural expansion in a tropical butterfly species with unusually expanded brain structures is linked to cognitive innovation. The study, published today in Current Biology, delves into the neural foundations of behavioral innovation in Heliconius butterflies. These butterflies, the only genus known to feed on both nectar and pollen, exhibit a remarkable ability to learn and remember spatial information about their food sources.
This ability has been associated with the expansion of a brain structure called the mushroom bodies, which are responsible for learning and memory.
“There is huge interest in how bigger brains may support enhanced cognition, behavioral precision, or flexibility. But during brain expansion, it’s often difficult to disentangle effects of increases in overall size from changes in internal structure,” Lead author Dr Max Farnworth from the University of Bristol‘s School of Biological Sciences explained.
In order to address this inquiry, the researchers delved into the alterations within the neural circuits that support learning and memory in Heliconius butterflies. Neural circuits are analogous to electrical circuits, with each cell forming specific connections and constructing a network to elicit specific functions through circuitry.
Upon conducting a detailed analysis of the butterfly brain, the team identified varying expansion rates among certain groups of cells known as Kenyon cells. This variability resulted in a pattern termed mosaic brain evolution, where some brain areas expand while others remain unchanged, similar to mosaic tiles differing from one another.
“We predict that because we see these mosaic patterns of neural changes, these will relate to specific shifts in behavioral performance – in line with the range of learning experiments which show that Heliconius outperform their closest relatives in only very specific contexts, such as long-term visual memory and pattern learning,” Dr. Farnworth explained.
Heliconius butterflies must establish efficient feeding routes due to the scarcity of pollen plants. This study significantly advances our understanding of how neural circuits adapt to drive cognitive innovation.
This research significantly advances our understanding of how neural circuits adapt to drive cognitive innovation and change. By studying neural circuits in easily studied model systems like insects, we can uncover genetic and cellular mechanisms that are common across all neural circuits. This has the potential to narrow the gap, at least on a mechanistic level, to other organisms, including humans.
In the future, the team aims to expand their study of neural circuits beyond the butterfly brain’s learning and memory centers. They also plan to enhance the resolution of their brain mapping to visualize how individual neurons connect at an even more detailed level.
“I was really fascinated by the fact that we see such high degrees of conservation in brain anatomy and evolution, but then very prominent but distinct changes,” Dr Farnworth said.
“This is a really fascinating and beautiful example of a layer of biodiversity we don’t usually see, the diversity of brain and sensory systems, and the ways in which animals are processing and using the information provided by the environment around them,” concluded Dr. Montgomery.
Journal reference:
- Max S. Farnworth, Theodora Loupasaki, Antoine Couto, Stephen H. Montgomery. Mosaic evolution of a learning and memory circuit in Heliconiini butterflies. Current Biology, 2024; DOI: 10.1016/j.cub.2024.09.069
