Structural homology of identified motoneurones in larval and adult stages of hemi‐ and holometabolous insects

Abstract

The set of neurones innervating the dorsal longitudinal muscles was studied with cobalt and nickel backfills in: (1) larval and adult locusts (Schistocerca gregaria and Locusta migratoria), (2) the larval and adult beetle (Zophobas morio), and (3) various segments of these insect species. In all specimens 11 neurones were encountered, which can be subdivided into a group of 7 motoneurones that stem from the next anterior ganglion and 4 neurones located in the ganglion of the segment containing the muscles. The latter group comprises 2 contralateral and 2 medial somata, of which one is a dorsal unpaired median neurone. The results were analysed under different aspects. This neural set and the basic structure of the dendritic fields is similar in: (1) different segments (serial homology), (2) the larval stage and imago of the same species with or without a pronounced metamorphosis (ontogeny), and (3) the studied hemi- and holometabolous insects (phylogeny). Our results support the notion that the structure of these neurones is conserved irrespectively of changes in the periphery and strategy of postembryonic development.

Crustacean – Insect Relationships: The Use of Brain Characters to Derive Phylogeny amongst Segmented Invertebrates

“…It is also significant that these early 20th Century researchers focused on brain structures, not ganglia, presumably recognizing from Retzius's work and confirmed by modern studies [e.g. Breidbach and Kutsch, 1994;Wolf, 1995] that ventral segmental ganglia were likely to show relatively fewer taxon-specific traits than brains. Indeed, 40 years before Holmgren, Flögel [1878] had compared the brains of flies, beetles, dragonflies, moths, and hemipterans, observing that although each brain comprised the same basic set of neuropils, the architecture of these neuropils in each family of insects appeared to have their own conserved and distinguishing characters.…”

Efferent neurons and specialization of abdominal segments in grasshoppers

“…Of the six motor neurons, five were contralateral and, of these, three were ovipositor motor neurons (protractors). Based on its cell body location and path of primary neurite, the single ventral medial motor neuron may be a common inhibitor (Watson et al, 1985;Breidbach and Kutsch, 1990). The effDUM neuron was distinguished by its paired axons, one in each tergal nerve.…”

On the Origin of Grasshopper Oviposition Behavior: Structural Homology in Pregenital and Genital Motor Systems

“…Segmental repetition and homology are widespread within insects and across insect species [Breidbach and Kutsch, 1990]. The A8 segment, however, is missing one of the usual 15 paired muscles in both males and females.…”