Sources of Variation in Seed Mass in Arum italicum

Abstract

Models on seed size/number trade-off predict a uniform size of seeds and a decrease in seed size with an increase in seed number. However, substantial between- and within-plant variation in seed size has been found. This study examined the accommodation of Arum italicum to predictions of models. Seed mass variation at population, plant, fruit and within-fruit levels and the existence of a size/number trade-off were examined. Considerable within-plant variation was found in seed mass. Seeds in upper fruits were smaller than seeds in lower fruits and caused variation in seed size. An unequal mass partition between seeds in multiseeded fruits was another source of within-plant variation in seed size. Seed number per fruit is likely to be determined by resource or pollen limitation, not by seed-packaging costs. No size/number trade-off was found at the single plant level. Seedling performance was positively related to seed size. Nevertheless, a maximum seed size seems to exist in this species, instead of a minimum size.