The Dynamic Wind-Pollinated Mating System

Summary

The dynamic wind-pollinated mating system in conifers is more than a random game of pitch and catch; orderly forces work towards maximizing chances of pollen capture while minimizing selfing and interspecific hybridization. Aerodynamics of moving branches, leaves and female strobili favor pollen movement into ovules while more cryptic molecular mechanisms influence paternal parent choice from pollination onward to seed maturity. Outcrossing is the general outcome for most conifers but a few interesting exceptions include mixed mating systems, selfing, hybridization, reproductive sterility and the singular case of paternal apomixis. Self-pollination occurs at moderate rates yet few selfed seed are recovered in some of the Pinaceae; most selfed embryos die before reaching maturity so this is known as the embryo lethal system. Hybrid matings can be blocked by a few pre-zygotic barriers but more often matings between close relatives produce viable, fertile F1 offspring without a change in ploidy. Conifer reproduction is often abundant to the point of nuisance; it is not unusual for a conifer's wind-pollinated mating system to have a genetic footprint extending tens or even hundreds of kilometres from adult trees. At the other extreme, rare cases of reproductive steri lity are reported for both the Pinaceae and the Cupressaceae.