Brain composition inHeliconiusbutterflies, 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 post-eclosion and experience-dependent plasticity between different brain regions.This analysis uncovers age-and experience-dependent post-eclosion 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.

The brain of a nocturnal migratory insect, the Australian Bogong moth

“…They possess a configuration of five neuropils that is shared across many species, consisting of the lamina, medulla, a lobula complex composed of the lobula and the lobula plate, and the accessory medulla. As expected from the nocturnal lifestyle of the Bogong moth, the total relative volume of the optic lobe is about 50% smaller than in the diurnal Monarch butterfly, consistent with data on other butterflies (Montgomery et al 2016). Interestingly, despite the overall size difference, the internal layout of each optic lobe neuropil is remarkably conserved between the two species.…”

“…These include a suboesophageal ganglion that is fused with the brain, well-developed optic lobes, large antennal lobes, a complex organization of the mushroom body with a multi-layered double calyx and an intricately organized lobe system. One feature of the mushroom body in particular appears to be a defining characteristic of moths and butterflies, namely the presence of the Y-tract with its associated lobelets (Heinze and Reppert 2012;Sjöholm et al 2005;Montgomery et al 2016;Homberg et al 1988). A second unusual feature of lepidopteran brains is that the PB of the CX is split across the midline, in contrast to other insects, in which this neuropil forms a continuous, midline-spanning structure (Heinze and Reppert 2012;Stöckl et al 2016;el Jundi et al 2009).…”

Mushroom bodies in crustaceans: Insect‐like organization in the caridid shrimp Lebbeus groenlandicus

“…Mushroom body elaboration in parasitoid Hymenoptera has been attributed not to the evolution of eusociality but to the evolution of olfactory spatial memory that informs the individual about the location and readiness of an intended host to receive the parasitoid's egg (Farris & Schulmeister, 2011). There is a direct relationship between the size of paired mushroom bodies and the ability to remember visual and olfactory cues used in the memory of locations during trap-line foraging (Montgomery, Merrill, & Ott, 2016), and comparisons of solitary bees showed those with foraging experience had the largest mushroom bodies (Withers, Day, Talbot, Dobson, & Wallace, 2008). In the ant Camponotus floridanus, experienced workers achieve about 50% enlargement of the mushroom bodies compared with base-line naïve workers (Gronenberg, Heeren, & Hölldobler, 1996).…”

Unraveling the functional organization of lobula complex in the mantis brain by identification of visual interneurons

“…Studying the response properties and morphology of LOX neurons in the mantis would provide us with fundamental knowledge for understanding the functional organization of the LOX. The LOX consists of two neuropils, the lobula plate and the lobula, in most holometabolous insects such as flies (Ito et al, 2014), beetles (Dreyer et al, 2010), and butterflies (Kinoshita, Shimohigashi, Tominaga, Arikawa, & Homberg, 2015;Montgomery, Merrill, & Ott, 2016). In contrast, the LOX consists of more than three neuropils in several hemimetabolous insects such as cockroaches, locusts, and mantises (Rosner et al, 2017).…”