Brain composition in Heliconius butterflies, posteclosion growth and experience-dependent neuropil plasticity

Abstract

Behavioral and sensory adaptations are often reflected in the differential expansion of brain components. These volumetric differences represent changes in cell number, size, and/or connectivity, which may denote changes in the functional and evolutionary relationships between different brain regions, and between brain composition and behavioral ecology. Here we describe the brain composition of two species of Heliconius butterflies, a long-standing study system for investigating ecological adaptation and speciation. We confirm a previous report of a striking volumetric expansion of the mushroom body, and explore patterns of differential posteclosion and experience-dependent plasticity between different brain regions. This analysis uncovers age- and experience-dependent posteclosion mushroom body growth comparable to that in foraging Hymenoptera, but also identifies plasticity in several other neuropils. An interspecific analysis indicates that Heliconius display a remarkably large investment in mushroom bodies for a lepidopteran, and indeed rank highly compared to other insects. Our analyses lay the foundation for future comparative and experimental analyses that will establish Heliconius as a valuable case study in evolutionary neurobiology.Grant sponsor: Research Fellowships from the Royal Commission for the Exhibition of 1851 and Leverhulme Trust; Grant sponsor: Royal Society; Grant number: RG110466; Grant sponsor: British Ecological Society Early Career Project Grant (all to S.H.M.); Junior Research Fellowship from King’s College, Cambridge, and an Ernst Mayr Fellowship from Smithsonian Tropical Research Institute (STRI) (both to R.M.M.); Grant sponsor: University Research Fellowship from the Royal Society,London (UK); Grant sponsor: BBSRC (UK); Grant number: BB/L02389X/1 (both to S.R.O.)