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1. Haemolymph amino acid, sugar and glycerol levels in the Namib Desert tenebrionid Physadesmia globosa (Coleoptera: Tenebrionidae) during dehydration and rehydration

Creator:
Naidu, Strinivasan
Type:
article, model:article, and TEXT
Subject:
Osmoregulation, Physadesmia globosa, Tenebrionidae, Namib Desert, amino acids, trehalose, and glycerol
Language:
English
Description:
Haemolymph levels of amino acids, sugars and glycerol were investigated in the tenebrionid Physadesmia globosa during dehydration and rehydration. The absolute amount of amino acid decreases during dehydration and increases during rehydration, indicating active regulation of this solute (the osmolal contribution of amino acids is large - approx. 25%). Changes in the amino acid content of the haemolymph during dehydration are not the result of interchange with soluble protein; the possibility exists during rehydration (between 1 h and 48 h). Trehalose and glucose are the only sugars found in appreciable quantity in the haemolymph of this species. Their osmolal contributions (total sugar: 2.6%), and contributions to osmoregulation, are not great. Glycerol is a minor osmolar effector in the haemolymph of Physadesmia, and changes in its levels do not contribute importantly to the regulation of haemolymph osmotic pressure.
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

2. Why does the Namib Desert tenebrionid Onymacris unguicularis (Coleoptera: Tenebrionidae) fog-bask?

Creator:
Naidu, Strinivasan G.
Type:
article, model:article, and TEXT
Subject:
Water balance, osmoregulation, lipid, Tenebrionidae, Onymacris unguicularis, Namib Desert, and glycerol
Language:
English
Description:
Dehydration of Onymacris unguicularis (Haag) for 10 days at 27°C resulted in a weight loss of 14.9%, and a 37% decrease in haemolymph volume. Although there was an overall decrease in the lipid content during this period, metabolic water production was insufficient to maintain total body water (TBW). Rehydration resulted in increases in body weight (6.2% of initial weight), TBW (to normality), and haemolymph volume (sub-normal at the end of rehydration). Despite an increase of 44.0 mg in the wet weight of O. unguicularis after drinking for 1h, there was little change in the water content at this time, although the total lipid content increased significantly. Increases in haemolymph osmolality, sodium, potassium, chloride, amino acid and total sugar concentrations during dehydration were subject to osmoregulatory control. No evidence of an active amino acid-soluble protein interchange was noted during dehydration or rehydration. Haemolymph trehalose levels were significantly increased at the end of rehydration (relative to immediate pre-rehydration values), indicating de novo sugar synthesis at this time. Osmotic and ionic regulation was evident during rehydration, but control of OP during haemolymph-dilution is poor and accomplished largely by the addition to the haemolymph of free amino acids and solute(s) not measured in this study. There was little mobilization of sodium and chloride ions from storage sites at this time. The lesser osmoregulatory ability of Onymacris unguicularis and perhaps earlier susceptibility to osmotic stress, a significantly high normal blood glycerol level (relative to other diurnal adesmiine tenebrionids), and a water storage mechanism associated with synthesis of fat, probably all contribute to the development of fog-basking behaviour in this species. Water gain in O. unguicularis during periods of relative drought is probably largely accomplished by a greater food consumption.
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public