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How evolutionary miniaturization in insects influences their organs

May 17, 2017

Scientists from the Faculty of Biology of the Lomonosov Moscow State University have studied out, how organs of microinsects change their sizes in the process of miniaturization -- reduction in sizes of incest bodies in the process of evolution. Looking ahead, principles and regularities of miniaturization, revealed in animals, could be applied in biotechnology and robotization. The researchers have presented their project in Scientific reports journal.

Alexey Polilov, Doctor of Biological Sciences and the article author says: "The project idea was to estimate how different insect organs react on body size changes. We focused on miniaturization -- namely, evolutionary reduction in body sizes up to extremely small sizes. We wanted to study out what happens to the structure of organs when insect body sizes decrease from one centimeter up to tenths of a millimeter. This is necessary to understand what remains the same and what changes in an insect body".

Miniaturization or reduction in body sizes appears to be one of the main tendencies of insect evolution, as a result of which they become the size of unicellular organisms. One of the smallest insects are Coleoptera and Hymenoptera, Mymaridae. Their size is about fractions of a millimeter and it's very difficult to see them with an unaided eye. These insects emerged hundreds of millions years ago and they have been evolving all this time -- up to present day.

Microinsects are around us: they fly in cities, in parks, mountains and forests. They are represented in Moscow, but in low latitudes and tropics there are more of them. These insects have specific wings, made not as a blade like in dragonflies but like a vein with bristles along the edges, looking like a feather.

The biologists have analyzed a vast amount of data, obtained during last ten years, devoted to the studies of structure of tiny insects. The scientists have created 30 complete and 26 partial 3D computer reconstructions for 22 insect species of 11 families¸ belonging to five orders (Thysanura, Psocoptera, Thysanoptera, Coleoptera, and Hymenoptera). Insects of various sizes have been studied -- their body volume differed by a factor of more than 150 000. On the basis on these models the biologists have analyzed relative volumes of insect organs.

Alexey Polilov shares: "We've revealed the fact that the majority insect organ systems demonstrate great opportunities for scaling, namely they constrain constant proportions by multiple changes of body sizes. Organ systems keep structure and some of them -- even constant relative volume, despite multiple reductions in sizes."

The scientists have found out that metabolic systems, tissues of internal environment and tracheal system decrease proportionally to the reduction in body sizes even in the smallest insects. However, reproductive and nervous systems, on the contrary, demonstrate multiple increase in relative volume as the body sizes decrease.

The scientist clarifies: "It seems that these very systems limit minimal body sizes in insects. Our results, being compared together with scientific literature on vertebrate animals, show that at the same allometry scales most organs in vertebrates change non-proportionally. So, we've shown that insect structure is better adapted to scaling and especially, to reduction in body sizes".

In the future the researchers are going to expand a range of studied objects due to covering insects from different orders, for instance, Collembola, Acari and other arthropods.

Lomonosov Moscow State University

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