Variation in the mineral composition of eggs of the snail, Helix aspersa between populations exposed to different levels of metal contamination Original Research

The eggs of terrestrial gastropods represent a major investment of resources by the parent, not least in the provision of essential metals. In this experiment 11 populations of Helix aspersa were collected from habitats with different histories of lead exposure and allowed to reproduce in the laboratory. After 4 months on a low metal diet, five four-egg samples were taken from a single clutch of each population and analysed for their metal content. Within-clutch and between population variation in the eggs were measured. No Pb or Cd was detected in any of the eggs. Both trace and essential metals show considerable variation between eggs within the same clutch. Cu levels were consistent across populations while egg Zn was closely correlated with soil Zn. Median Ca and Mg levels show little relation to soil concentrations. However, Ca provision declines with soil Pb across the populations. While the metal content of the eggs appears to be closely regulated, an interaction between Pb and Ca in the parental tissues may mediate the supply of Ca to the eggs.