Neutral Lipids in Snail Conditioned Water from Two Strains ofHelisoma trivolvis(Gastropoda: Planorbidae)

Abstract

Densitometric thin-layer chromatography (TLC) was used to study neutral lipids in snail conditioned water (SCW) from two strains ofHelisoma trivolvis(Colorado and Pennsylvania strains). Snail conditioned water with feces (SCW-WF) and snail conditioned water without feces (SCW-WOF) were analyzed. Free sterol was the major lipid fraction released during the first 2 h of incubation by the Colorado (CO) and the Pennsylvania (PA) strains. The major neutral lipid fraction in SCW-WF released by the CO strain within 4 h postincubation was free sterol, while the major fraction released within 4 h by the PA strain was free fatty acid. The mean ± SE of free sterol released within 4 h by the CO and PA strains, 0.6 ± 0.1 and 3 ± 2 μg per snail per ml of water, respectively, was not significantly greater than that released within 2 h, 0.5 ± 0.2 and 0.1 ± 0.5 μg per snail per ml of water, respectively. The free fatty acid released within 4 h by the CO and PA strains, 0.3 ± 0.1 and 4 ± 2 μg per snail per ml of water, respectively, was significantly greater than that released within 2 h, 0.04 ± 0.01 and 0.10 ± 0.02 μg per snail per ml of water, respectively. The major neutral lipid in SCW-WOF at 2 h postincubation was free sterol for both strains. The mean ± SE of free sterol released within 4 h by the CO and PA strains, 0.7 ± 0.2 and 0.9 ± 0.8 μg per snail per ml of water, respectively, was not significantly greater than that released within 2 h, 0.6 ± 0.2 and 0.7 ± 0.2 μg per snail per ml of water, respectively. By 4 h postincubation, the major neutral lipid in SCW from both strains was free fatty acid. The mean ± SE of free fatty acids released within 4 h by the CO and PA strains was 0.7 ± 0.5 and 3.1 ± 0.5 μg per snail per ml of water, respectively. The free fatty acid fraction released within 2 h by the CO and PA strains was below the quantification level of the experiment, 0.12 μg per snail per ml of water for each strain. Snails also released a hydrocarbon fraction that was not quantified. The lipids in the fecal and mucous extracts of both snail strains were analyzed qualitatively by TLC, and the zones were similar to those seen in the analyses of SCW-WF. However, the zones were more intense in fecal than in mucous extracts. The significance of these neutral lipids as chemoattractants remains to be determined.