Anatomical reconfiguration of the optic lobe during metamorphosis in the blow fly Calliphora vicina (Diptera: Calliphoridae) revealed by X-ray micro-computed tomography

Abstract

Unlike most larval organs and tissues, the central nervous system of holometabolous insects persists into the adult stage, although profoundly remodelled and with some neuropils largely newly formed during metamorphosis. Among the neuropils, those forming the optic lobes are particularly relevant as they are the visual processing centres and comprise more than half of the neurons of the adult insect brain. Using micro-CT, we document the morphological remodelling of the optic lobe during metamorphosis in the blow fly Calliphora vicina Robineau-Desvoidy, and provide quantitative measures of volumetric changes in its neuropils. In addition, we compare these qualitative and quantitative changes to those in two neuropils of the central brain: the antennal lobe and the central complex. The most profound reconfigurations occur between the pupal stage and the beginning of the pharate adult stage, when the neuropils of the optic lobe rotate 90°, and during the pharate adult stage, when the lamina unfolds and extends below the newly formed retinular cells. There is a slow increase in volume of the neuropils of the optic lobe during the pupal stage and the beginning of the pharate adult stage, followed by a major increase in volume during the second half of intra-puparial development.