Blogpost #8: A Matter of Selection - Sydney Stitt

Introduction 

Natural selection seems to have affected plants for thousands - maybe millions, of years. Natural selection and adaptation allows specific traits best fit for the environment to succeed, as less-fit traits soon become extinct.

Brassica oleracea, the species we're currently working on, is no exception to natural selection. Like many other species on our planet, brassica plants came from a common ancestor - wild cabbage. Yet it's been hundreds to thousands of years since adaptions from wild cabbage began - leaving plenty of room (and time) for mutations, gene shuffling (caused by meiosis) and random assortment of genetic material to create different variations and traits.

The many different types of brassica plants clearly exemplify these variety of traits. As I studied the plants one day, I noticed how different these plants seemed to appear. The phenotypes of many of these plants were completely unlike one another! Some plants had spindly, purple spikes with a semblance of petals, while others were much more similar to their ancestors with large, thick leaves with a rounded physique.

Questions

1a) What part or characteristic of the Brassica oleracea plants seems to exhibit the most variation?

It was clear that the reproductive system, or the anatomical reproductive parts of each plant, seemed to differ the most. None of the different types of brassica displayed the same phenotype when it came to the reproductive system. Take this picture I took to the right, of one of the flowers (the reproductive system of one of the brassica plants). With soft yellow petals and long stalks, it's incredible different from one of the other plants. The second image above is of another brassica plant, with spindle petal-like parts and much shorter stalks. A third picture to the left shows another floral area of a different brassica plant, with a tan tone color and thinner spike-like sections. 

1b) What part of characteristic of the Brassica oleracea plants seems to show the greatest range of variation?

Despite these flowers having the most variation, the one part of each brassica plant that displayed the largest range of variation seemed to be the leaves. Some leaves were teeny tiny - others were huge and overwhelming (the cabbage leaves for sure).

Not only were the physical dimensions of the leaves full of variation, but the textures of the leaves' surfaces and the edges as well. The most common textures seemed to be smooth, bumpy, and a hybrid between both smooth and bumpy. As for the edges, ragged (or random sharp edges) and smooth were the most populous. Here is a table showing all of the varying leaves.

	Leaf
	Width	16 cm	13 cm	10 cm	1.5 cm	8 cm
	Length	19 cm	24 cm	14 cm	6 cm	6 cm
	Edge	Ruffled	Ragged	Ragged	Spiked	Smooth
	Texture	Bumpy	Bumpy	Bumpy	Smooth	Smooth

	Leaf
	Width	14 cm	8 cm	14 cm	8 cm
	Length	9 cm	22 cm	19 cm	11 cm
	Edge	Ragged	Ragged	Ragged	Ragged
	Texture	Smooth	Smooth/bumpy (mix)	Smooth/bumpy (mix)	Smooth/ bumpy (mix)

Here is an image of a graph I made to show the juxtaposing average surface areas of the leaves. As you can see, there are both very large and very small surface areas, as well as medium sizes.

2) Why is there so much variability in domestic forms of Brassica oleracea?

Species naturally evolve to adapt to their environment. Thus, domestic forms of Brassica oleracea must have evolved to naturally fit in their environment. Their ancestor, the wild cabbage, is typically in the northern areas of Western European. However, as the species moved from place to place, (most notably, from Northern Europe to North America), the species must've adapted to the massively different climates. Northern Europe's climate is quite colder, windier and overall receives more rain and snow. North America's climate is somewhat varied, with massive snowfall in some areas, yet more likely to have a drier, sunnier climate. Additionally, due to the survival aspect, the plants would likely die if they were unable to adapt to their environment. In this case, taller plants are likely to survive much better in a North American climate, because winds are less powerful and less likely to knock down a tall plant.

However, wild cabbage is quite similar to regular cabbage (one of the different types of Brassica oleracea, which happens to be my group's plant). This is likely due to the idea of descent with modification, when the descendants of a common ancestor have similar traits. This is also known as heredity, where the traits of the parent are passed down to their offspring.

As for natural variation and mutation in terms of how it affects variability in the species, they refer to more random alterations in the gene pool. Mutations can cause a random effect, such as leaf texture or color, to change the plant. If this change is favorable, then natural selection would choose it to be passed down to other generations. Natural variation changes the traits given, from crossing over and random assortment. This simply means descendants of the common ancestor may have different traits due to mutations and natural variations within the plant.

As technology furthers in complexity, artificial selection and selective breeding becomes more and more imminent. Both options are most likely caused by a desirable phenotype, such as large leaves, a certain hue of the plant, etc. For instance, many farmers prefer larger, more bountiful plants for agricultural means. Thus, they would definitely want to certain favorable traits and/or genes together. Cross breeding and other means are used to breed two different brassica plants together with said favorable traits. In this process, a cross-breeder may take the male sperm of a specific plant, such as pollen, and place it upon the female's reproductive system. This way, the chances of the favorable traits and/or genes to be passed down are higher than leaving to natural selection or genetic drift (random events that change the gene pool of a species).

3) Which part of the Brassica oleracea plants seems to be the most consistly the same in all of the examples of our garden, regardless of how extreme the differences between other parts of the same plants may be? Why do you think so? Again, use and include data collected from multiple measurements to support your answer.

The anatomical part of the Brassica oleracea that seems to be the most consistent is the hue, brightness and saturation of the plant. All of the plants seem to have a muted forest green color to it. Of course, all plants are usually green, but it is the hue of the color that truly matters. I mainly focused on the hues, saturation and brightness levels of the leaves, because it is the part of the plant with the most distinct colors.

	Plant
	Color	Forest green	Murky green	Murky green	Forest green	Forest green
	Brightness	Muted	Muted	Somewhat muted	Muted	Very muted
	Saturation	Medium hue	Medium hue	Medium/light hue	Medium hue	Medium/dark hue
	Additional Colors	N/A	Pale purple	Light yellow	Light yellow	Pale purple

	Plant
	Color	Forest green	Forest green	Forest green	Forest green
	Brightness	Muted	Muted	Muted	Muted
	Saturation	Medium hue	Medium hue	Medium hue	Medium hue
	Additional Colors	Light yellow	Pale purple	Light yellow	N/A

As you can see, while there are a few outliers in the group, most (7/9) of the plants have a forest green shade. 8 out of the 9 plants are muted to some degree, and all of them have a medium level of saturation (not too pale, not too saturated with color). While there are quite different additional colors (purple and yellow are the most common), it is simply the way the additional color appears. All of these colors are pale, as in, not too much saturation of color.

The most likely reasoning behind this similarity is natural selection, as well as the always-present chlorophyll in the plant. The chlorophyll gives the plant a similar green color. As for the brightness and saturation, natural selection probably found it best fit for the plant to have that level of brightness/saturation to survive. In terms of predation, the muted tone allows the plants to blend in better from predators.

4) What would plant breeders have to do in order to get the body part or characteristic you described above (in your response to question #3) to become much more different than it is presently?

Plant breeders would have to alter the levels of chlorophyll if they truly wanted to change the color and hue. Since much of this is dependent on natural selection, it is difficult for a breeder to easily alter it. They would have to find a plant that happens to not be a forest green color (quite difficult when most all plants in this species are forest green) and keep mating the non-forest green plants together until they discard of the forest green colors.