CALCIUM PROVISION TO EGGS IN TWO POPULATIONS OF HELIX ASPERSA BY PARENTS FED A DIET HIGH IN LEAD

Abstract

The reproductive performance of two populations of Helix aspersa with different histories of exposure to lead was assessed by their egg production, hatching success and the metal content of the eggs. By using laboratory-bred parents raised in a Pb-free environment, the possibility of an inherited response to a high Pb exposure was assessed. Following a period of dormancy, six individuals in each population were paired for copulation and allowed to oviposit. During this time they were fed a diet with 500 pg.g-' Pb, for a total of 14 days. After oviposition, the egg mass from each pairing was weighed, counted and samples analysed. Metal concentrations in four tissue fractions of the parents (shell, hepatopancreas, reproductive system and 'rest') were also analysed. There was no significant transfer of Pb to the eggs in either population. There were differences in their egg masses-the population from an uncontaminated site, Rottingdean (RD), laid, on average, twice the number of eggs of the snails from Minera (MI), a contaminated site in North Wales. However the latter had a higher average percentage emergence (90% compared to 55% for RD). There was also considerable hatching asynchrony in the RD offspring, while hatching within each MI egg mass was completed within two days. This is discussed in relation to the Ca status of the parent and possible differences in reproductive strategy between the two populations.