BIOCHEMICAL EVALUATION OF AESTIVATION AND STARVATION IN BULINUS GLOBOSUS AND BULINUS ROHLFSI SNAIL SPECIES

Abstract

There is resurgence in incidence of schistosomiasis in Nigeria with attendant socio-economic and health impact. The agents transmitting this disease are the Bulinus snails which employ aestivation to survive conditions of unfavourable weather such as lack of food and water. The mechanism of aestivation under aridity and drought is not clear. This study therefore investigated the effects of aestivation and starvation on endogenous metabolic reserves in tissues and haemolymph of two snail species namely Bulinus globosus (morelet) and Bulinus rohIfsi (Clessin). Aestivation, starvation and control experiments were set up for 30 days in the laboratory by placing three groups of snails collected in dry and rainy seasons from Oyan dam, Abeokuta in standard aestivation slope (30 B. globosus and 19 B. rohlfsi), aquarium (30 B. globosus and 23 b. rohifsi) while control slope had 20 B. globosusl. and 15 B. rohlfsic. Aestivation and control slopes contained water and mixture of sand and clay (3:1) while aquarium contained water only for starvation. All the snails were fed on lettuce and libitum for 28 days during which water was completely drained out in the aestivation slope. The aestivation slope and aquarium were left for another 30 days without lettuce. Snails were thereafter sacrificed and protein, carbohydrate and lipid contents in tissues and haemolymph determined. Haemolymph creatinine, urea, total protein, glucose, total cholesterol and triglyceride were also determined. lsozyme expressions and activities of lipase, α-amylase, NADP-dependent isocitrate dehydrogenas, alanine amino transferase (ALT) and aspartate amino transferase (AST) were determined. Thin Layer Chromatography (TLC) for detection of free Fatty acids was conducted. Physicochemical properties of water samples from the sites were determined using standard methods. Data were analysed using ANOVA. Tissue macromolecules decreased in aestivating and starving snail during dry and rainy seasons compared with controls but was significant (p<0.05) for lipid and carbohydrate. Lipid content in B.globosus and B.rohlfsi (28.92±8.00% versus 76.36±16.00%) in dry season and (72.02±8.00% versus 72.12±9.00%) in rainy season respectively. Carbohydrate contents for B.globosus and B. rohlfsi were similarly depressed (64.64±11.00% versus 70.19±11.00%) in dry season and (41.79±9.00% versus 83.00±7.00%) in rainy season respectively. In aestivating and starving B.globosus, haemolymph creatinine, urea, total protein, glucose, ALT and AST were were significantly decreased while haemolymph concentrations of total cholesterol, triglyceride and cc-amylase activity increased significantly (p<0.05). In B.rohlfsi, creatinine, urea, ALT and AST were significantly dcereased compared with controls (p<0.05). No genetic polymorphisms in NADP-dependent isocitrate dehydrogenase, α-amylase and lipases were observed. There was an increase in lipase activity during aestivation and starvation suggesting lipolysis. Among both species, TLC detected cholesterol and triglyceride during aestivation but not starvation. Physicochemical analysis of water showed that all the snails thrived better in oxygenated, slightly acidic (pH 5.6), low turbidity and low saline water. B.globosus seems a better aestivator than B.rohlfsi in terms of physiological adaptations to aestivation induced stress. Aestivation rather than starvation seems a better way of preserving snails under unfavorable conditions as lipids and carbohydrates are more efficiently utilized compared with starvation.