Mushroom body variation in beetles (Coleoptera): A challenge for future research

Abstract In insects, attention has only been focused on the neural underpinnings of learning and memory in some model species such as the fruit fly Drosophila melanogaster or the bee Apis mellifera . Current literature also includes a detailed description of the mushroom bodies (MBs), the part of the brain that is responsible for these abilities. An interesting group for similar studies in insects could also be beetles (Coleoptera); they are probably the largest animal group in terms of species, with an extraordinary morphological and ecological diversity that is also reflected at the neurobiological level. The morphological complexity of the MBs does not appear to be directly related to the position of the beetle family in the evolutionary tree, as taxa across evolutionary ranks have similar MB structures when exposed to similar adaptive pressures and lifestyles. Different levels of MB complexity are evident among related species across various families. In beetles, the entire spectrum of MB organisation can be observed: from simple (or absent) calyxes, with a small number of Kenyon cells and undivided MB lobes, through various degrees of compartmentalisation and enlargement of the synaptic surface, to an MB structure similar to Hymenoptera, some of whose representatives exhibit an exceptional level of associative learning. The structure of the MB can be regarded as an adaptive trait, evolving in response to selection pressures dictated by the efficiency and flexibility of behavioural output during information processing in the MB, which results from the interaction of the brain, the body and the environment.