Abstract
How animals perceive, process and respond to environmental cues is tightly tuned to the species-specific demands imposed by their ecology and life history. This specialisation is likely reflected in neural systems that support sensory perception and memory recall. In the Neotropical butterflies, Heliconius, the mushroom bodies, insect integration, learning and memory centres, are significantly expanded in comparison with those of their closest relatives. The mushroom body calyx, which is innervated by projection neurons from primary sensory centres, is particularly expanded due to an increased volume processing visual information. This suggests that visually orientated behaviours explain selection for mushroom body expansion in this genus. Indeed, mushroom body expansion in Heliconius coincided with the evolution of a novel dietary shift towards active pollen feeding, and a spatial foraging behaviour, traplining, which is thought to require long term spatial memory of visual scenes.Here, I explore the relationships between sensory neuroanatomy and modality-specific shifts in behaviour across species in Heliconiini. I tested long-term olfactory memory using an assay of food–odour associations in Heliconius and non-Heliconius species, and compared visual and olfactory memory performance. There were no differences in the long-term olfactory memory across Heliconiini species. Combining data from olfactory and visual memory trials confirms a significant difference in performance among sensory modalities between Heliconius and outgroup genera. Analyses of eye structure, estimated visual acuity, neural investment in visual brain structures and the major tracts between them showed conservation of the sensory anatomy across Heliconiini. This further supports the evidence that, in Heliconius, the evolution of cognitively demanding trapline foraging behaviour has occurred as a result of a specific and localised specialisation of the mushroom bodies. These data provide a rare case where there is sensory-modality-specific brain evolution that has facilitated cognitive enhancements.
| Date of Award | 10 Dec 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Stephen H Montgomery (Supervisor), Max Farnworth (Supervisor) & Denise Dalbosco Dell'Aglio (Supervisor) |