Changes in the Hepatopancreas Metabolic Reserves of Porcellio laevis Latreille During Starvation and the Moult-Cycle

Abstract

The cycle of growth and moulting in Porcellio laevis is described. The criteria developed for distinguishing the moult-stages of the adult are based on gross and obvious morphological changes occurring in the cuticle prior to, during and just after exuviation. Porcellio laevis undergoes at least eight moults to reach maturity. During the nymphal life, the body length increases regardless of moulting. After maturity, the increase in the body length occurs only after exuviation. The major portion of the glycogen present in the hepatopancreas is stored inside the mature epithelial cells, while the lipids are contained in both the mature and the transitional epithelium. The effect of prolonged starvation (of 20 28 days) is to lower the hepatopancreatic glycogen contents to approximately 5 7% of the values observed in fully fed adults. The lipid contents, however, remain unaffected. Evidence is presented to show that the hepatopancreatic lipid reserves, built up during anecdysis, represent the major energy source in this crustacean during its moult-cycle. The significance of these findings is discussed. INTRODUCTION The cyclical accumulation of organic reserves is a significant feature of crustacean physiology (Adiyodi, 1969). These reserves for the most part stored inside the hepatopancreatic cells subsequently are used extensively for the formation of the new exoskeleton prior to periodic moulting. Many reports on the interrelationship of the accumulation of the organic reserves inside the hepatopancreatic cells and the moult-cycle in decapod crustaceans have been published (Huggins and Munday, 1968). However, studies on the moult physiology of isopods are scattered, fragmentary and often inconclusive; and, indeed, no complete study of any one species has ever been done. The present investigation is concerned with the study of the process of moulting in, and the moult physiology of a terrestrial isopod, Porcellio laevis Latr. MATERIALS AND METHIODS Porcellio laevis used in this study were drawn from a stock colony, and maintained on pieces of carrot in a glass tank at 21 C and 100%l relative humidity. For biochemical analysis, 10th-12th instar woodlice were dissected in 0.85% iced saline. After the removal of unwanted adhering tissue, the hepatopancreas were dried in vacuo over calcium chloride until no weight change was recorded. Lipid contents were determined by the technique of Steeves (1969), and the glycogen levels were estimated by the colorimetric micromethod of Kemp and Kits van Heijningen (1954). Both lipid and glycogen estimates are