Differential rates of seed abortion among trees of Dalbergia sissoo: role of post-dispersal sibling competition

Abstract

It has been suggested that production of a high frequency of few-seeded pods in most trees of Dalbergia sissoo is due to the enhanced dispersal efficiency and reduced sibling competition among the seeds of such pods. However, a few trees exhibit a relatively low seed abortion and hence, a relatively lower frequency of one- and two-seeded pods. Such reduced seed abortion in one such tree (T-9) is shown to be due the lack of establishment of a strong dominance by the early fertilized over the late fertilized ovules. Unlike in the pods of the normal trees, the early fertilized ovules in this tree do not inhibit the metabolic activity of the late fertilized ovules. We show that such reduced abortion in such trees is favoured due to reduced gains to the survivor in the few-seeded pods. While the dispersal advantage of the single-seeded over many-seeded pods in this tree remains the same as in others, the post-dispersal negative interactions among the seeds of a pod are significantly lesser in it than that in the pods of normal trees. We discuss these results in the context of sibling rivalry among, and inclusive fitness of, the seeds developing within the pods of D. sissoo.