According to museum collections from the early 1900s, the population of one beetle species in California’s central valley used to have individuals with different colors, including red, blue, yellow and brown. The beetles were found feeding on various native plants. 50 years after almond farming became widespread, most beetles were brown-colored and found living on the bark of almond trees. Observations indicate that birds are the primary predators of beetles. Question: How and why did the population of beetles evolve to be primarily brown in color?Sentence 1: Describe the variability that was initially present in the population. Sentence 2: State which individuals in the population had the highest fitness during the event or change (if any), and why. Sentence 3: Explain what evolutionary force acted on the population, and why and how it acted. Sentence 4: Describe how the population evolved in response. Be as specific as you can (e. g., say "increased" or "decreased", rather than just "changed".)

Answer and Explanation:

Data:        

How and why did the population of beetles evolve to be primarily brown in color?

The populations probably went through a process of directional selection, turning mostly to the brown-color, probably due to a better capability of camouflaging on vegetation and hiding from birds.

Sentence 1: Describe the variability that was initially present in the population.

Initially, there were many colors of the invertebrate, such as red, blue, yellow, and brown. These beetle populations used to feed on many vegetable diversity, which probably also had a great variety of colors.

Sentence 2: State which individuals in the population had the highest fitness during the event or change (if any), and why.

Brown individuals were the ones with the highest fitness, as they were able to camouflage on the new widespread almonds. The fact was probably that this dark-colored farming became bigger each time, occupying areas where there used to be native vegetable species of many colors. Due to this change in the vegetation color, all the colored beetle species were highly exposed and in a very disadvantageous position that directed them to be predated by birds, who could see them better. Brown individuals, on the other hand, were capable of escaping from predation because they were able to hide on the almonds.

Sentence 3: Explain what evolutionary force acted on the population, and why and how it acted.

Directional selection was the force acting on the population. Directional selection increases the proportion of individuals with an extreme phenotypic trait; in the exposed example this trait is the brown color. This selection occurs more frequently in those cases in which interactions between living organisms and the environment modify in the same direction. Initially, native vegetable species of many colors were living in an area where, after a few years, almond invaded. The general color of the space then changed. In order not to be seen by the birds that preyed on them, directional selection acted on the beetles to turn them brown-colored, so they camouflaged better with vegetation and avoided being eaten by birds.    

Sentence 4: Describe how the population evolved in response. Be as specific as you can (e.g., say "increased" or "decreased", rather than just "changed".)

Probably there was an initial decrease in the number of individuals due to an increase in their predation. After this event of predation, only brown individuals got to survive, which suggests an important decrease in the total population size. If the survival individuals got to adapt, probably their reproductive rate increased enough to stabilize the population again.