Patterns of Intrafruit Seed Abortion and Variation in Seed Mass of the Guanacaste Tree (<scp><i>Enterolobium cyclocarpum</i></scp>, Fabaceae) in Populations From Mexico and Costa Rica

Abstract

Analyses of the variation in the abortion rate and mass of seeds of tropical trees are scarce, despite their importance in modulat- ing seed production, plant recruitment, and herbivore foraging patterns. We studied these reproductive processes in a tropical dry forest tree species. We studied the patterns of intrafruit abortion and seed mass in fruits of the Guanacaste tree, Enterolobium cyclocarpum, in samples of trees from 5 populations in Mexico and Costa Rica. We analyzed the effects of developmental phase, fruit and maternal tree effects, and seed position within the fruit on the abortion rate and mass of seeds from mature and im- mature fruits. Naturally pollinated flowers were studied to determine the patterns of ovule fertilization within the ovaries. Overdispersion of the abortion rate per fruit within trees and a higher frequency of abortions in the extreme positions of the fruit were common patterns in all populations. These patterns were observed from the beginning of fruit formation. Ovules in the sty- lar position do not have higher survival rates, despite their precedence in fertilization. A negative relationship was found between abortion events and seed mass. Fruit-­ specific fertilization and developmental conditions seem to be the main factors driving the fruit abortion rate and seed mass, causing high variability in seed survival and mass within maternal trees. The correlation be- tween the fruit abortion rate and seed mass may be related to the capacity of the fruit to drain maternal resources. These patterns are common to all studied Guanacaste tree populations.