Anatomy of the smallest coleoptera, featherwing beetles of the tribe nanosellini (Coleoptera, Ptiliidae), and limits of insect miniaturization

Abstract

The internal structure of Nanosella sp., Primorskella sp., and Porophila sp. was described from serial sections and total preparations using light and transmission electron microscopy. The most important structural features related to miniaturization are the absence of midgut muscles, abortion of two Malpighian tubes, a decrease in the number of abdominal spiracles, strong reduction of the tracheal system, the absence of the heart, reduction of the circulatory system and its substitution by the fat body, strong oligomerization and concentration of the nervous system, a decrease in the size and number of neurons, and reduction of the left testis and left ovary. The internal structure of featherwing beetles was analyzed for the first time using 3D computer models, which allowed us to demonstrate changes in the relative volume of organs accompanying the body diminution. The excretory and digestive systems change isometrically, while others change allometrically. The relative volume of the musculature decreases, and that of the nervous and reproductive systems increases. The skeleton mass also increases. The possible factors limiting further diminution in Ptiliidae (egg size, the volume of the reproductive and nervous systems, and the skeleton mass) are discussed. © 2008 MAIK Nauka.