Evaluation of anticoagulants and hemocyte-maintaining solutions for the study of hemolymph components in the spiny lobster Panulirus argus (Latreille, 1804) (Decapoda: Achelata: Palinuridae)

Functional studies on humoral or cellular responses in the hemolymph of crustaceans require the selection of suitable anticoagulant- and hemocyte-maintaining solutions. We studied the suitability of several anticoagulant- and hemocyte-maintaining solutions in the spiny lobster Panulirus argus (Latreille, 1804), with emphasis in the preservation of hemocyte number and viability. It was found that the modified Alsever solution was the ideal anticoagulant, while modified L-15 medium and Panulirus argus saline (PAS) were the best hemocyte-maintaining solutions. It is striking that whereas avoiding plasma clotting is relatively simple to achieve, avoiding lysis and aggregation of hemocytes could be challenging and variable among closely related crustaceans. The reasons are hardly known and might indicate different composition or sensitivity of both membrane-bound and soluble mediators in any of the three types of hemocytes identified among decapod crustaceans. Hemolymph volume average in P. argus was 10.5% of fresh body weight (more than 50 ml per adult individual), which makes this species an attractive model for functional studies of hemolymph components in crustaceans.

Sodium distribution predicts the chill tolerance of Drosophila melanogaster raised in different thermal conditions

Many insects, including the model holometabolous insect Drosophila melanogaster, display remarkable plasticity in chill tolerance in response to the thermal environment experienced during development or as adults. At low temperatures, many insects lose the ability to regulate Na+ balance, which is suggested to cause a secondary loss of hemolymph water to the tissues and gut lumen that concentrates the K+ remaining in the hemolymph. The resultant increase in extracellular [K+] inhibits neuromuscular excitability and is proposed to cause cellular apoptosis and injury. The present study investigates whether and how variation in chill tolerance induced through developmental and adult cold acclimation is associated with changes in Na+, water, and K+ balance. Developmental and adult cold acclimation improved the chilling tolerance of D. melanogaster in an additive manner. In agreement with the proposed model, these effects were intimately related to differences in Na+ distribution prior to cold exposure, such that chill-tolerant flies had low hemolymph [Na+], while intracellular [Na+] was similar among treatment groups. The low hemolymph Na+ of cold-acclimated flies allowed them to maintain hemolymph volume, prevent hyperkalemia, and avoid injury following chronic cold exposure. These findings extend earlier observations of hemolymph volume disruption during cold exposure to the most ubiquitous model insect ( D. melanogaster), highlight shared mechanisms of developmental and adult thermal plasticity and provide strong support for ionoregulatory failure as a central mechanism of insect chill susceptibility.

Water acquisition and partitioning inDrosophila melanogaster: effects of selection for desiccation-resistance

SUMMARYWe examined physiological features related to water balance in five replicate populations of Drosophila melanogaster that have undergone selection for enhanced resistance to desiccation (D populations) and in five replicate control (C) populations. Adult D flies contain 34 % more water than the control flies. We examined two hypotheses for increased water acquisition in the D flies: (i) that they accumulate more water early in development and (ii) that they have a reduced post-eclosion diuretic water loss. We found no evidence of differential water or dry mass acquisition between the C and D populations prior to adulthood. We also found no evidence of differential post-eclosion diuresis, i.e. both C and D groups showed insignificant changes in water volume in the 4 h period immediately after eclosion. In addition, we quantified water content in the intra- and extracellular compartments of the C and D populations and were able to identify the hemolymph as the primary storage site of the ‘extra’ water carried by the desiccation-resistant flies. We estimated that 68 % of the increased water volume observed in the D flies was contained in the hemolymph. Desiccation-resistance was strongly correlated with hemolymph volume and only weakly with intracellular water volume. Survival during desiccation was also strongly related to the carbohydrate content of the D flies. It has been presumed that the D flies accumulate carbohydrate primarily as intracellular glycogen, which would result in a significant increase in intracellular water volume. We found that carbohydrate content was weakly correlated with intracellular water volume and more strongly with hemolymph volume. The carbohydrate pool in the D flies may, therefore, be contained in the extracellular compartment as well as in cells. These results are suggestive of the importance of modifications in hemolymph volume and hemolymph solute concentrations in the evolution of enhanced desiccation-tolerance in populations of Drosophila melanogaster.

REGULATION OF PULMONARY BLOOD FLOW AND OF BLOOD PRESSURE IN A MANGROVE CRAB (GONIOPSIS CRUENTATA)

The air-breathing mangrove crab Goniopsis cruentata ventilates the branchial chambers with its scaphognathites (SG). Ventilation is predominantly in the forward direction, but is punctuated by bouts of reversed pumping. Reversals are more frequent when crabs are in air than in water, and yet more frequent during respiratory stress (hypoxia or exercise). Reversed SG pumping is tightly coupled with bursts of impulses to the dorsal-ventral muscles (DVM) which span the anterolateral thorax. Phasic contractions of the DVMs increase the hemolymph pressure in the dorsal sinuses. These pressure pulses help drive hemolymph through the lungs. The coupled SG reversed ventilation and DVM-assisted increases in lung perfusion appear to be an adaptation to increase gas exchange at the lungs. When crabs are made hyper- or hypotensive by changes in hemolymph volume, the EMG activity of the DVMs dramatically decreases or increases, respectively. The resultant expansion or constriction of the dorsal sinuses is an effective baroreceptor reflex producing short-term adjustments in hemolymph pressure.