The Effects of Miniaturization on the Anatomy of Corynoneura scutellata Winnertz, 1846 (Diptera, Chironomidae), One of the Smallest Dipterans.

Miniaturization is a widespread trend in animal evolution. In insects, the effects of miniaturization have been described at all the levels of body organization, from major rearrangements of organ systems to fundamental changes at the cellular level. The results of studies on the anatomy of tiny beetles, wasps, booklice, thrips, and strepsipterans have contributed significantly to understanding the process of miniaturization in animals. However, not all the orders of microinsects have been sufficiently well investigated so far. In this paper, the internal structure of the adult male of one of the smallest nematocerans, the midge Corynoneura scutellata Winnertz, 1846 (Diptera: Chironomidae), is described in detail for the first time using 3D computer reconstructions based on serial histological sections. Despite the tiny body size, most organ systems retain the ground plan typical of the larger representatives of related groups. The tracheal system of C. scutellata has not lost its high level of organization, being represented by large tracheal trunks and a branching system of tracheae. The ganglia of the central nervous system are concentrated, while the head muscles and those associated with the intestine are reduced. The changes in the relative volumes of the organ systems in tiny dipterans are analyzed in comparison with microinsects from other orders. The previously revealed general patterns of organ allometry are valid for tiny dipterans as well, but the reproductive system of C. scutellata has a considerably smaller relative volume, as compared with that of microinsects from other orders. [ABSTRACT FROM AUTHOR]