SEASONAL-VARIATION IN SIZE AND NUTRIENT CONTENT OF EGGS OF THE LAND SNAIL ARIANTA-ARBUSTORUM

Variation in size and nutrient content of eggs deposited in successive batches is a life-history aspect that has received little attention. We examined the size and nutrient content of eggs laid in successive b atches by the land snail Arianta arbustorum. Snails from three populat ions (a lowland, a subalpine and an alpine locality in Switzerland) di ffered in number of batches produced, clutch size, egg size and nutrie nt concentration and energy content of eggs. This was partly due to di fferences in shell size, since reproductive characters of A. arbustoru m scale with shell size. In the first batch snails from the lowland an d subalpine population laid eggs that had a higher protein concentrati on (28.1%) than snails from the alpine population (25.6%). Similarly, eggs from the first batch did not differ in carbon concentration in th e lowland and subalpine population, whereas eggs from the alpine popul ation had a lower concentration. Clutch size tended to decrease in suc cessive egg batches in all populations. Egg size increased over the re productive season in snails from the lowland population, whereas no se asonal change was observed in the subalpine and alpine population. Pro tein concentration decreased in successive batches in the lowland and alpine population but tended to increase in the subalpine population. Carbon concentration decreased over the season in the lowland populati on but not in the other two populations. This indicates (1) egg charac teristics show different changes in successive batches in different sn ail populations, and (2) the trade-off clutch size vs. egg size can be influenced by alterations of the nutrient concentration and energy co ntent of eggs.