Seedling Establishment from One- and Two-Seeded Fruits of Cryptantha flava: A Test of Parent-Offspring Conflict

Abstract

This study uses the relative performance of one- and two-seeded fruits of the semidesert perennial Cryptantha flava to evaluate an earlier hypothesis that the parent plant and its offspring conflict over optimal seed number per fruit (brood size). Under this hypothesis, parents should favor large brood sizes in order to increase offspring number and reduce the amount of pericarp required per seed, whereas each offspring should favor increasing its own mass at the expense of other brood members. The fruits of C. flava, like most multiovulate, indehiscent fruits, commonly mature a single seed, but a few mature more than one. This pattern of seed production has been viewed as evidence that the offspring have won the conflict. The current study shows that in C. flava, a seed (nutlet) initially benefits by being the only one in the fruit. Emergence was greater from seeds of one-seeded fruits than from the smaller seeds of two-seeded fruits, but two-seeded fruits were more likely to yield at least one seedling. On the basis of these data, the parent and offspring have different optimal brood sizes. However, the number of offspring resulting from the multiplicative effects of emergence and survival did not differ for the two fruit types. At one of two sites, higher mortality occurred among individuals growing in pairs than among single individuals. Several reasons are presented, in addition to the possibility of sibling competition, for why the parent could also favor bearing mostly single seeds. Whether a trade-off exists between brood size and number of fruits per plant must be determined before the potential for parent-offspring conflict can be fully evaluated.