When you read the title of this post, did you say to yourself “Well, it’s green, of course, that is if it is alive.” Doug firs (Douglas fir, Pseudotsuga menziesii) have some parts that aren’t green, however, and those parts are a visual confirmation of an important property of life – genetic variation in a population.
If you look at the branch tips of a Douglas fir early in the spring, you may notice its cones. This is provided that it is making cones that year. These trees don’t make cones every year. Each year some will form a few cones, but in a cone year, almost all the trees in an area grow cones at the same time. I’m not sure how they manage this trick, but it is a good one for a wind-pollinated species.
Like other conifers, Doug firs have pollen cones and ovulate (aka seed) cones. Both pollen and seed cones grow on the same tree – the species is monoecious. I’ve noticed that the Doug firs where I live have different colors of cones. Some of my trees have deep rose ovulate cones, while others have lemon yellow ones. The pollen cones on the tree match the color of the ovulate cones, but they aren’t quite as intensely colored.
As the ovulate cones develop, their characteristic three-pointed bracts protrude from between the cone scales. Most Doug firs around here have straight bracts, but some have curly bracts. The straight or curly feature remains after the cones have dried and fallen from the tree.
Why should Doug firs have different colors of cones and different types of bracts? I certainly can’t tell you the exact advantage, but I do know that variations in every population are important. They are that species’ library of solutions to life’s problems. Life tinkers – tries this and that. Some traits may work better for some situations, while others may be an advantage in different conditions.
No organism can predict the future, so the best survival strategy is to have lots of genetic diversity. This is the reason for cross pollination and sexual reproduction. The species that shuffles its genes and deals them out in all combinations has the best change of continuing on, whatever the environmental conditions.
Certainly there are some species that don’t seem to change, at least on the surface, but they just change more slowly. I prefer the term “slow-evolving species” to “living fossil” because the latter gives the false impression that the species doesn’t have variations and doesn’t change. Today’s ginkgoes are not the same as the Triassic ones, even if the leaves look the same.
When you are out in the field with your children, point out the variations that you can see. There may be an albino among a stand of blue flowers or some that have different shades of color. These are outward manifestations of genetic diversity in the population. Many more traits that we can’t see have variations in a natural population, and that’s a good thing for long term survival. Hurray for being different – diversity is an important characteristic of life.