Life History of the Land Snail Arianta arbustorum Along an Altitudinal Gradient

SUMMARY (1) The life history of the polymorphic land snail Arianta arbustorum was investigated in five natural populations along an altitudinal gradient from 1220 to 2600 m in the Swiss Alps. In order to assess the environmentally-induced variation of reproductive characters snails were transplanted to the lowlands. (2) Adult size decreased from 19-9 to 16-0 mm (mean shell breadth) with increasing altitude, age at maturity increased from 1-9 to 5-0 years, but median adult longevity and adult survival rates were approximately the same at all altitudes. (3) Clutch number, clutch size, egg size and reproductive investment per year decreased with increasing altitude in resident snails, whereas reproductive investment per egg increased. Within populations, clutch number, number of eggs produced per year and egg size scaled allometrically with shell size indicating a size-specific fecundity. (4) Transplanted snails laid 1-3-11-5 times more clutches than did resident snails. However, no differences in clutch size, egg dry weight and hatching success were found between transplanted and resident snails, except in one population, in which transplanted snails laid smaller clutches with larger eggs and scored a lower hatching success. (5) Transplanted snails were less variable in reproductive characters than resident ones, except for hatching success. (6) In general, life-history characters did not appear to be correlated with shell or body colour. (7) Although proximate factors like temperature explain most of the variation in life history, evidence was obtained also for genetic divergence among populations. The results match the predictions of the adversity selection model well, rather than those of bet