Ultrastructure of the fat body in the soil centipedes Lithobius forficatus (Lithobiidae) and Geophilus flavus (Geophilidae) according to their seasonal rhythms

Abstract The behavior, metabolism and physiology of animals are regulated by seasonal and/or circadian rhythms. The main aim of this study was to describe all of the alterations that are connected with the structure, ultrastructure and histochemistry in the fat body according to the seasonal cycles in centipedes. We selected the common European and long-living centipedes Lithobius forficatus and Geophilus flavus (Myriapoda, Chilopoda) as the material for this study. The fat body, which is the organ that is responsible for the accumulation of organic and non-organic material, was isolated from adult males and females in three seasons – spring, summer and autumn. However, some of animals that were collected in the autumn, were placed in aquaria and kept in a refrigerator (the temperature was about 0–4 °C) in order to stimulate the winter. The analysis revealed that the fat body in both of the species of centipedes formed irregular lobular masses that were composed of adipocytes, which fill the hemocoel and surround the internal organs. The adipocytes are responsible for the accumulation of the reserve material; the main reserve material are lipids. However, some polysaccharides, mucopolysaccharides and proteins were also detected. Seasonal changes, which are primarily connected with the accumulation of the reserve material and organelles that are responsible for synthesis, occurred in the cytoplasm of the adipocytes. Additionally, there was a distinct relationship between the amount of reserve material, the number of vacuoles and the intensity of autophagy in the cytoplasm of the adipocytes.