Sibling Competition and Evolution of Pollen Unit, Ovule Number, and Pollen Vector in Angiosperms

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Abstract
The pollination biology of angiosperms affects the quantity and quality of seeds produced by an individual. The amount of genetic variability present in the seeds of a single fruit is dependent on the number of male parents involved in fertilization. The variation in genetic relatedness of developing siblings in an ovary may lead to varying degrees of competition among young seeds for maternal nutrients. Kin selection theory predicts that closely related seeds resulting from fertilization by a single paternal parent will compete less with each other than seeds fertilized by different fathers. Random dispersal of single pollen grains characteristic of wind pollination tends to produce less closely related seeds in multi-ovulate ovaries. Pollen transferred between flowers in large aggregations by specialized animal pollinators gives rise to seeds that are full siblings. The evolution of animal pollination, large pollen unit size, and multi-ovulate ovaries in some angiosperms may be understood in terms of competitive interactions among the developing seeds.