The nitrogen requirements and dietary nitrogen utilization for the gecarcinid land crab Gecarcoidea natalis

The nitrogen requirements for tissue maintenance, moulting, and oogenesis were determined experimentally for the herbivorous land crab Gecarcoidea natalis. The maintenance nitrogen requirements for intermoult animals was very low (4.83 ± 1.68 mmol N kg-1 dry body wt d-1), but during oogenesis the total requirement was much higher (8.6 mmol N kg-1 dry body wt d-1). Gecarcoidea natalis could potentially assimilate enough nitrogen from rain forest leaf litter or leaves of Ficus of Erythrina to satisfy not only the maintenance nitrogen requirements but the observed rate of incorporation of nitrogen into the ovaries during oogenesis. The ovaries developed slowly over a period of 2 mo (mid-July to late September) and had a final nitrogen content of 359 ± 15.9 (n = 18) mmol kg-1 dry body wt. This was equivalent to 9.3% ± 0.4% of the total body nitrogen. A substantial nitrogen debt was incurred during ecdysis (658 ± 126 mmol kg-1 dry body wt). This nitrogen debt could be satisfied slowly, from leaf litter, over a period of 1-3 mo. After ecdysis, the majority of the nitrogen and urate within the animal prior to moulting was retained within the soft crab (85.0% ± 1.2% total nitrogen, 82.0% ± 1.2% nonurate nitrogen and 99.56% urate), while only a minority was lost with the exuviae (18.0 ± 1.2% total nitrogen, 14.7 ± 1.2% nonurate nitrogen, and 0.4% ± 0.4% urate). The urate deposits in G. natalis were not mobilized as a source of nitrogen in animals maintained on a nitrogen-free diet.