Altitudinal variation in size and composition of eggs in the land snail Arianta arbustorum

Egg size and egg provisioning are crucial for the survival of offspring in invertebrates without postlaying egg care. The effects of elevation and siz e of the mother on egg size and on nitrogen and carbon concentrations in eg gs were examined in eight populations of the land snail Arianta arbustorum over an altitudinal gradient from 370 to 2340 m in Switzerland. The dry mas s of single eggs ranged from 1.48 to 2.79 mg and decreased with increasing altitude. Adult snail size (shell volume) also decreased with increasing el evation as did clutch size and reproductive investment (clutch size x egg d ry mass) of mothers. Hatching success of eggs varied among populations, but showed no altitudinal pattern. When differences in parental shell size wer e taken into account, correlations between altitude and egg size, clutch si ze, and reproductive investment disappeared. Thus, the altitudinal decrease s in egg size, clutch size, and reproductive investment were mainly due to smaller snail sizes at higher elevations. The nitrogen concentration in egg s ranged from 3.3 to 4.5% and decreased with increasing elevation. In contr ast to egg and clutch size, the altitudinal variation in nitrogen concentra tion of eggs cannot be explained by differences in snail size. The carbon c oncentration in eggs ranged from 31.1 to 33.1%, but showed no altitudinal v ariation. Nitrogen and carbon concentrations in the eggshell and egg fluid in eggs from four populations were examined separately. The nitrogen concen tration in the eggshell ranged from 0.7 to 1.8% and was lower than that of the egg fluid (5.1-5.8%). Similarly, the carbon concentration in the eggshe ll was lower (20.2-22.8%) than that in the egg fluid (35.8-40.2%). Interpop ulation differences in egg composition may affect growth, size, and surviva l of hatchlings and the extent of egg cannibalism in A. arbustorum.