Storage and translocation of integumentary calcium during the moult cycle of the terrestrial isopod Oniscus asellus (L.)

Abstract

The calcium content of pieces of integument of standardized size from various regions of the body was measured at all 15 stages of the intermoult cycle. Calcium resorbed from the posterior integument during premoult is stored mainly in the sternal calcium deposits of the anterior region, which contain 20% of total body calcium in late premoult. Earlier arguments that the deposits are not a store of calcium are refuted. These deposits are similar to gastroliths in both structure and function. After posterior ecdysis, calcium in the deposits is resorbed rapidly and employed in calcification of the new posterior exocuticle. Calcium is then resorbed from the general anterior integument within 24 h and may accumulate transiently in the haemolymph. During this period resorption of integumentary calcium and calcification proceed simultaneously in the anterior and posterior regions of the animal. Ecdysis of the anterior region then occurs, and calcium from the haemolymph is employed in calcification of the new anterior exocuticle. Forty-eight percent of intermoult calcium content is conserved. However, both exuviae are eaten and it is argued that further calcium is conserved by resorption from the exuviae within the gut. It is suggested that this calcium, together with dietary calcium, is employed in calcification of the endocuticle after ecdysis. It is proposed that comparable events occur in all crustaceans that conserve calcium, but are rendered especially dramatic in isopods, owing to the unusual biphasic pattern of cuticle secretion.

Amorphous and crystalline calcium carbonate distribution in the tergite cuticle of moulting Porcellio scaber (Isopoda, Crustacea)

“…A study on the hemolymph calcium concentration of P. scaber revealed that calcium remains elevated after the anterior moult, suggesting another source for calcium ions (Ziegler and Scholz, 1997). P. scaber ingests the exuviae after each half moult, suggesting that the intestinal epithelium resorbs mineral from the exuviae that still contains considerable amounts of calcium carbonate (Steel, 1993). It is of interest that in the mineralizing cuticle many pore canals can be seen that are devoid of mineral.…”

“…This biphasic moult allows the animals to reduce the loss of CaCO 3 by shifting it between the anterior and poster integument. This mode is generally utilized in terrestrial isopod species (Oniscidea) that developed large CaCO 3 -deposits within the ecdysial space between the new and old cuticle of the first four anterior sternites (Messner, 1965;Steel, 1993;Strus and Compere, 1996;Ziegler and Miller, 1997;. Deposition and resorption of the deposits is well studied in the common woodlouse Porcellio scaber (Ziegler, 1996(Ziegler, , 1997Hagedorn and Ziegler, 2002;Ziegler et al, 2002Ziegler et al, , 2004Fabritius and Ziegler, 2003).…”

“…During this premoult stage calcium and carbonate ions are resorbed from the posterior cuticle into the hemolymph and are then transported into the ecdysial space of the anterior sternites where it forms the deposits. When the sternal deposits are well developed, additional CaCO 3 is stored within the anterior cuticle as indicated by a change in color resulting in a whitish appearance of the anterior dorsal part of the body including the anterior thoracic segments (tergites) (Steel, 1993;Strus and Blejec, 2001). After moult of the posterior, but before the moult of the anterior half of the body (intramoult) calcium and carbonate ions from the deposits and the anterior dorsal integument are transported back to the hemolymph and are used to mineralize the new posterior cuticle (Messner, 1965;Steel, 1993;Ziegler et al, 2007).…”

Calcite distribution and orientation in the tergite exocuticle of the isopods Porcellio scaber and Armadillidium vulgare (Oniscidea, Crustacea)

“…Like all Crustacea, in a process called moulting, isopods regularly shed the old cuticle and produce a larger one in order to grow. During the moulting cycle terrestrial isopods resorb ACC from the cuticle and store and recycle it to mineralise the new cuticle Numanoi, 1934;Steel, 1993;Ziegler, 1997;. Since ACC is about 10 times more soluble than crystalline calcium carbonate phases (Brečević and Nielsen, 1989), high relative amounts of ACC within proximal layers make perfect sense, when large amounts of calcium carbonate need to be stored and recycled in order to quickly restore the protective function of a thick cuticle (Hild et al, 2008).…”

Expression and polarity reversal of V-type H+-ATPase during the mineralization–demineralization cycle in Porcellio scabersternal epithelial cells

“…Isopods molt by shedding first the posterior and then the anterior half of their mineralised cuticle and replace it by a new larger one to allow for growth. About 1 week before the molt, terrestrial species resorb Ca 2+ and HCO3 -from the posterior cuticle and store it between the old cuticle of the first four anterior sternites and the anterior sternal epithelium (ASE) as large CaCO3 deposits (Messner, 1965;Steel, 1993). For this to occur, Ca 2+ and HCO3 -are transported from the hemolymph across the ASE to form the deposits.…”