Question

Background: 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?

Your answer:

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 1

The population of beetles evolved to be primarily of brown color, as described below;

• During early 1900, when the almond cultivation was not widespread, the species of beetle had individuals with different color such as- red, blue, yellow, brown, all having equal chances of survival.
• But during the event of cultivation of almond trees, the brown coloured beetles were found to have higher fitness and greater chances of survival.
• Due to extensive and widespread cultivation of almond trees and loss of the native plants, the evolutionary force of natural selection acted upon the brown coloured beetles to increase their chances of survival, as they could not be easily spotted and caught by the predator birds, due to resemblance of their color with that of the bark of almond tree where they inhabit.
• Hence, gradually the number of brown coloured beetles increased during the course of evolution, to have a population of beetles primarily of brown color.