I already talked a bit about goldenrod hybrids and chromosomes. I will talk later about goldenrod reproductions, but briefly, they produce seeds that blow around (sexual reproduction) and rhizomes that spread underground (asexual reproduction). As a result of mutation, sexual reproduction, and hybridization, there is considerable genetic variation within any one species of goldenrod, and within any one population of a single species.
The photos at the top of this post are an example (all three are Solidago juncea, early goldenrod, July 30, 2021). They are growing on the same side of the same road, all within the same five-meter stretch of roadside. One is almost done blooming, one is in the middle of blooming, and one has yet to bloom. Yes, there could be some environmental differences between the locations of these plants, but it is highly unlikely that such minor differences would account from the considerable differences in phenology. No, the differences are mostly genetic, and are representative of the amount of genetic variation in goldenrods.
As it turns out, genetic variation has a measureable effect on what goes on in a field of goldenrods. Among the early goldenrod plants along my road, the differences might make it impossible for the earliest and the latest blooming plants to cross pollinate.
But there is more.
Gregory Crutsinger and his colleagues examined the significance of genetic diversity in an excellent field experiment published in 2006. First, they had to find a variety of goldenrods and clone them (they used tall goldenrod, S. altissima). Goldenrods are easy to clone because they spread vegetatively, but it takes time to grow enough clones. This experiment required long-term planning. And they didn’t merely assume that the different plants were genetically different. They compared the DNA of the different clones using a method called amplified fragment length polymorphism (AFLP). As expected, and confirmed, there were differences in the DNA between clones.
They planted the goldenrods in plots at a density of stems equivalent to those in many goldenrod fields in northeastern North America (12 stems per square meter). All plots had the same number of stems, but some plots had only one genotype, while others had three, or six, or twelve genotypes. They replicated each type of plot many times, and scattered each type of replicate throughout their test field to avoid bias by location. In short, they did it right.
They identified the arthropods (insects and arachnids) on the plants during the growing season, and measured the growth of the plants.
So what happened? The graphs show us what happened.
On average (the horizontal black bars among the circles), the greater the genetic diversity of the plants, the more species of herbivores, the more species of predators, and the more species of all arthropods were found in the plots (richness means the number of species). And the greater the genetic diversity, the greater the total growth of the plants in the plots (they measured growth as above-ground net primary production, ANPP).
The graphs show a lot of variation among the plots, and that the effects were statistically significant. Increased genetic diversity resulted in 20-35% increases in the average values of various measurements, which I would say is functionally significant.
I would not have predicted this much of an effect of the genetic differences among goldenrods of the same species, so I am delighted that someone else took the time to test it.
And I think it is highly likely that genetic variation within other plant species is also significant. Back in the 1970s, Janus Antonovics cloned a bunch of grasses that he collected in the wild, and checked to see whether the clones grew differently, whether alone or in competition with other clones. They did.
So genetic variation matters within a species.
When we talk about biodiversity (how many species in a habitat, region, or the planet), we need to include genetic diversity. Genetic diversity is the foundation for all diversity.
Gregory M. Crutsinger et al 2006. Plant genotypic diversity predicts community structure and governs an ecosystem process. Science 313: 966-968
You might have noticed the green sphere-like structures among some of the flowers in the pictures. Those are galls were produced by a species of gall midge (tiny flies). I hope to explore those in a future post.