Seasonal variation in size and nutrient content of eggs of the land snailArianta arbustorum

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Abstract
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 batches by the land snail Arianta arbustorum. Snails from three populations (a lowland, a subalpine and an alpine locality in Switzerland) differed in number of batches produced, clutch size, egg size and nutrient concentration and energy content of eggs. This was partly due to differences in shell size, since reproductive characters of A. arbustorum scale with shell size. In the first batch snails from the lowland and subalpine population laid eggs that had a higher protein concentration (28.1%) than snails from the alpine population (25.6%). Similarly, eggs from the first batch did not differ in carbon concentration in the lowland and subalpine population, whereas eggs from the alpine population had a lower concentration. Clutch size tended to decrease in successive egg batches in all populations. Egg size increased over the reproductive season in snails from the lowland population, whereas no seasonal change was observed in the subalpine and alpine population. Protein 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 population but not in the other two populations. This indicates (1) egg characteristics show different changes in successive batches in different snail populations, and (2) the trade-off clutch size vs. egg size can be influenced by alterations of the nutrient concentration and energy content of eggs.