Influence of aestivation on the survival of Galba truncatula (Mollusca : Gasteropoda) populations according to altitude

Field and laboratory studies on 11 populations of Galba truncatula were per formed to determine the survival rate of snails after aestivation, to speci fy the range of their shell heights, and to establish the percentage of G. truncatula which burrowed in soil when summer drying occurred. These invest igations were performed using six lowland populations living in central Fra nce (alt. 206-282 in) and five highland populations, located in the Massif central (alt. 806-900 in). The survival rate of G. truncatula after floodin g dried soil with water was significantly higher in the highland than in th e lowland populations (69.5-80.7 % in road ditches, for example, instead of 29.3-33.0 %). The mean shell heights of surviving snails and the durations of snail re-activation in water did not show any significant variation, wh atever the origin of snail population. The percentages of snails buried in drying soil were higher in the highland population (13.0 and 15.0 % of juve nile snails, for example, instead of 4.0 % and 7.7 % in lowland snails). In the lowland population only young snails buried, whereas 5.8-8.3 % of adul ts in the highland population were partially burrowing. The local climate o f the sites studied in the Massif central, and the ability of snails to bur row into the mud when stagnant water disappeared in July, might explain the higher survival rate during aestivation.