Developmental mechanisms, homology and evolution of the insect peripheral nervous system

Abstract

Segmentally homologous neurogenesis and neuronal differentation processes characterize the formation of th insect peripheral nervous system. These processes have been analyzed at the level of identified neurons and nerv branches in the grasshopper. During early embryogensis a simple peripherial nerve scaffolding is established in each body segment. This scaffolding consists of serially reiterated segmental nerves, which are pioneered by homologous sensory neurons differentiate in a stereotyped spatiotemporal pattern in each segment and project their axons onto these nerves. Data on serial homology in the development of the peripheral nervous system, which were obtained on the basis of comparative structural and developmental data in the grasshopper, are supported by a large body of developmental and genetic data abtained using Drosophila wildtype and mutants. Indeed, a comparison of the results obtained in the grasshopper with those obtained from Drosophila shows that virtually the same pattern of peripheral nerves and major structures is formed in both species. These findings indicate that the construction of the peripheral nervous system in extremly divergent modern insects relies on conserved developmental mechanisms that evolved in ancestral insects over 300 million years ago.