Polilov Alexey A
Department of Entomology, Faculty of Biology, Lomonosov Moscow State University, Moscow, Russia.
PLoS One. 2017 May 3;12(5):e0175566. doi: 10.1371/journal.pone.0175566. eCollection 2017.
The body size, especially in cases of extreme reduction, is an important characteristic that strongly determines the morphology, physiology, and biology of animals. Miniaturization is a widespread trend in animal evolution and one of the principal directions of evolution in insects. Miniaturization-related features of insect morphology have been subject to intensive studies during the last few years, but the structure of the smallest insects remains insufficiently known. It is especially important to study hymenopterans of the genus Megaphragma, which include the smallest flying insects and a species in which an almost anucleate nervous system was recently discovered. This article is the first detailed study of the external and internal morphology of adults of Megaphragma mymaripenne and M. amalphitanum using histological methods, 3D computer modeling and other techniques. It is shown that in spite of the extremely small size the organization of Megaphragma retains a considerkable level of structural complexity. On the other hand, miniaturization leads to re-organizations of several organ systems. Unique structural features related to miniaturization have been found in both species: lysis of cell bodies and nuclei of neurons at late stages of pupal development, absence of the heart, and considerable reductions in the set of muscles. Comparative analysis of structure in the smallest insects representing different taxa has revealed common features of the evolutionary process of miniaturization in insects.
体型大小，尤其是在极度缩小的情况下，是一个重要特征，它强烈地决定着动物的形态、生理和生物学特性。小型化是动物进化中的一个普遍趋势，也是昆虫进化的主要方向之一。在过去几年里，昆虫形态学中与小型化相关的特征受到了深入研究，但最小昆虫的结构仍然了解不足。研究膜翅目巨膜翅属昆虫尤为重要，该属包含最小的飞行昆虫，且最近在其中一个物种中发现了几乎无核的神经系统。本文首次运用组织学方法、三维计算机建模及其他技术，对米氏巨膜翅和阿玛尔菲塔巨膜翅成虫的外部和内部形态进行了详细研究。结果表明，尽管体型极小，但巨膜翅的组织结构仍保持着相当程度的结构复杂性。另一方面，小型化导致了几个器官系统的重新组织。在这两个物种中都发现了与小型化相关的独特结构特征：蛹发育后期神经元细胞体和细胞核的溶解、心脏缺失以及肌肉数量的大幅减少。对代表不同分类群的最小昆虫的结构进行比较分析，揭示了昆虫小型化进化过程的共同特征。
