INLUENCE OF SAMPLING DATE ON REPRODUCTION IN THE LAND SNAIL HELIX APERTA KEPT UNDER CONTROLLED CONDITIONS OF TEMPERATURE AND PHOTOPERIOD

International audienceReproductive traits of Helix aperta snails were investigated snider four combinations of temperature and photoperiod (20 degrees C/16hL:8hD; 20 degrees C/8hL:16hD; 15 degrees C/16hL:8hD and 15 degrees C/ 8hL:16hD). Three samples were used: Sample 1 and Sample 2 collected from Annaba (Northeastern Algeria) during and after hibernation respectively; Sample 3, previously studied (unpublished data), collected from Bejaia (near Northeastern Algeria) during aestivation. All the snails began to mate on the first week and to lay on the 3(rd)-4(th) week of setting under conditions of reproduction. Sample 1 and Sample 2 were characterized by shorter reproduction periods (4-6 weeks) than Sample 3 (5-7 weeks). Strikingly, although most of the snails collected during and after hibernation mated at a high rate (56-87 %) in comparison with those collected during aestivation (32-92 %), their rates of egg-laying were drastically lower (6-25 % against 12-80 %). Among the snails that had mated, only 11-36% laid eggs in Samples 1 and 2 against 38-87% in Sample 3. The mean numbers of eggs per clutch were higher in Sample 1 (293-323) and Sample 3 (337-348) than in Sample 2 (237-248) (P < 0.05). Inversely, the mean egg weights per clutch were heavier in Sample 2 (17.5-17.8 mg) than in Sample 1 (16.1-16.3 mg) and Sample 3 (16.3-16.6 mg) (P < 0.05). After the reproduction period, as a consequence of differential reproductive yields, the mean weights of snails very significantly increased in Sample 1 and Sample 2 (P < 0.001) and significantly decreased in Sample 3 (P < 0.05). Reproductive performances were more affected and lethality rates higher under low temperature and short day photoperiod: The best combination of temperature and photoperiod was mostly 20 degrees C/16hL:8hD, conditions closer to those in the field during autumn, especially overnight, the phase of snail activity. After the reproduction period, the lethality was becoming higher and higher and the surviving snails were less active or trying to burrow themselves into the soil of the egg-laying pots. All these arguments plead that H. aperta snails are better adapted to reproduce in autumn (decreasing days and higher temperatures) after a long aestivation stimulating gametogenesis than in spring (increasing days and lower temperatures) after hibernation inhibiting gametogenesis