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We report the novel discovery of anucleate neuron cells in a miniature wasp.
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A mostly anucleate CNS is capable of sustaining many functions exhibited by other insects with nucleated neurons.
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Smallest insects have only about 7,400 cells in their central nervous system.
The smallest insects are comparable in size to unicellular organisms. Thus, their size affects their structure not only at the organ level, but also at the cellular level.
Here we report the first finding of animals with an almost entirely anucleate nervous system.
Adults of the smallest flying insects of the parasitic wasp genus Megaphragma (Hymenoptera: Trichogrammatidae) have only 339–372 nuclei in the central nervous system, ie. their ganglia, including the brain, consist almost exclusively of processes of neurons. In contrast, their pupae have ganglia more typical of other insects, with about 7,400 nuclei in the central nervous system. During the final phases of pupal development, most neuronal cell bodies lyse. As adults, these insects have many fewer nucleated neurons, a small number of cell bodies in different stages of lysis, and about 7,000 anucleate cells.
Although most neurons lack nuclei, these insects exhibit many important behaviors, including flight and searching for hosts.
[Keywords: miniaturization, Megaphragma, Trichogrammatidae, anucleate neurons]
…A detailed study of the nervous system based on serial histological sections using 3D computer modeling and transmission electron microscopy shows that the central nervous system of adult M. mymaripenne displays considerable oligomerization and concentration of ganglia, with the thoracic ganglia merged into a single synganglion positioned mostly in the metathorax, and the abdominal ganglia merged into a single synganglion. The brain of M. mymaripenne occupies a large part of the space within the head capsule (Figure 2). The brain and other ganglia consist almost exclusively of neuropil (Figure 3–D) similar in appearance to that of larger insects.
The central nervous system contains only 339–372 (M = 361, n = 3) nuclei, with 179–253 (M = 215, n = 3) of them in the brain (Figure 2C, D). These numbers are extremely low compared to adults of larger wasps in the genus Trichogramma of the same family that have about 37,000 nucleated neurons in the brain. The central nervous system of M. mymaripenne occupies 6% of the body volume, 2.9% by the brain. This ratio is markedly different form larger hymenopterans (eg. Apis, honeybees) in which the brain occupies 0.35%–1.02% of body volume and 0.57% in ants of the genus Formica (1976; 1953) and 3.2% in Chalcidoidea, a parasitic wasp of the genus Hemiptarsenus.