Intracellular purine deposits in the gecarcinid land crabGecarcoidea natalis

Abstract

The terrestrial crab Gecarcoidea natalis stores large amounts of purine in the body. The major component of the purine deposits is urate (85% of the total purines). The other 15% is comprised of hypoxanthine, guanine, and xanthine. Microscopy studies reveal that these urate deposits are located intracellularly in spongy connective tissue cells throughout the body. Urate exists as numerous membrane-bound crystals 1 µm in diameter. Vesicles thought to represent urate vesicles at various stages of development are also present in the cytoplasm of the cell. Few organelles are visible in the urate storage cells, and it is unlikely that the urate is synthesized on site. Crabs (N 5 2) fed a high-nitrogen diet have greater numbers of urate storage cells at more connective tissue sites, and the cells are larger (36.3 6 1.8 µm (mean 6 SE) and 44.0 6 1.4 µm (mean 6 SE)) and contain more urate than urate storage cells in animals collected from the field (N 5 3) or maintained in the laboratory on a low-nitrogen diet (N 5 1). The mean diameter of urate storage cells in animals fed a diet low in nitrogen and field-collected animals ranges from (13.5 6 0.5 µm (SE) 2 22.3 6 1.0 µm (SE)). This histological study supports a strong correlation between purine accumulation and the nitrogen content of the diet.

Ammonia excretion in aquatic and terrestrial crabs

“…In Cardisoma guanhumi the fluid retained within the abdominal flap (~13.5·mmol·l -1 ) is contiguous with that in the branchial chamber (~6.5·mmol·l -1 ) and further NH 4 + excretion may occur via unknown mechanisms (Wolcott, 1991) but, even so, this would be unavailable to land crabs in the dry season. Purine is stored in large amounts in connective tissue cells throughout the bodies of some land crabs (Linton and Greenaway, 1997b). In Gecarcoidea natalis this stored purine is normally synthesized de novo, from excess dietary nitrogen (Linton and Greenaway, 1997a).…”

Terrestrial adaptations in the Anomura (Crustacea: Decapoda)

“…Purine is stored in large amounts in connective tissue cells throughout the bodies of Coenobita and B. latro, (Henry and Cameron, 1981;Greenaway and Morris, 1989) as well as other land crabs (Linton and Greenaway, 1997a). In the brachyuran land crab Gecarcoidea natalis (Pocock, 1888), this stored purine is synthesised de novo, and it is likely that synthetic ability is common to the brachyuran and anomuran land crabs that store purines (Linton and Greenaway, 1997b).…”

Subcuticular Urate Accumulation in an American Lobster (Homarus americanus)

“…6,12 Uric acid can be a precursor for urea following the actions of uricase, allantoinase, and allantoicase. 6,13 Urea can be subsequently hydrolysed by urease to ammonia and CO 2 . 6,12 American lobsters, as other aquatic crustaceans, are ammonotelic-ammonia is the main nitrogenous waste product, with only minimal amounts of urea and uric acid produced under normal conditions.…”

“…Intracellular urate deposits in the land crab Gecarcoidea natalis were found in spongy connective tissues throughout the body, including the subcuticular tissues, within specialized urate storage cells. 13 Accumulations could be quite extensive and were positively correlated with dietary nitrogen content. The authors speculated that the urates were being absorbed by and stored in the cells rather than being directly synthesized, as there was little in the way of cellular organelles present.…”

“…The authors speculated that the urates were being absorbed by and stored in the cells rather than being directly synthesized, as there was little in the way of cellular organelles present. 13 The deposits were also considered as a potential storage site for nitrogen reserves. Notably, these deposits did not deform the overlying exoskeleton.…”