Self-fertility variation and paternal success through outcrossing in Douglas fir

Douglas fir trees, Pseudotsuga menziesii, vary greatly in their self-fertility, but little is known about the relationship of self-fertility to outcrossing success. If low self-fertility pollen donors have lethal recessive alleles that are widespread, then in crosses with other trees they should have poor paternal success competing with high self-fertility donors that have few recessive lethals. We compared Douglas fir trees with high and low self-fertility for differences in pollen grain size, pollen number per milligram, and respiration rate. Pair-wise mixtures of pollen from individuals with high and low self-fertility were applied in controlled pollinations. Electrophoretic markers identified seed paternity. The pollen donors did differ in all three pollen traits but, as a class, the low self-fertility donors had neither inferior pollen nor low paternal success in outcrossing. Paternal success depended upon the identity of the competing pollen donors and the seed parent. It was not related to pollen grain number or respiration rate, but donors with the smaller pollen grains in a mixture had greater success.