Lecture Notes: Evolutionary Adaptation of Rock Pocket Mice

Introduction to the Valley of Fire

• Location: New Mexico
• Geological Feature: Volcanic eruptions 1,000 years ago created black lava patches amid the desert.
• Environmental Impact: Changed the natural habitat, affecting species dependent on camouflage.

Rock Pocket Mouse Adaptation

• Natural Camouflage:
  • Light-colored mice blend into desert sands.
  • Stand out against dark lava, making them prey to visual predators (e.g., foxes, coyotes, rattlesnakes, owls).
• Evolutionary Pressure: Predators exert selective pressure, favoring mice that blend in with their background.

Evolutionary Mechanics

• Role of Mutation:
  • Mutations are random changes in genetic material.
  • A mutation led to dark fur, advantageous on black lava.
• Natural Selection:
  • Non-random process determining survival based on advantageous traits.
  • Dark fur provides a competitive edge on lava, leading to population-wide adaptation.

Genetic Basis of Fur Color

• Research by Michael Nachman:
  • Extracted and compared DNA from light and dark mice.
  • Identified the Mc1r gene as responsible for dark fur due to four chemical letter changes.
• Rapid Adaptation:
  • Mutation spread due to reproductive advantage associated with camouflage.
  • Mathematical Model: A minor competitive advantage can lead to widespread adoption within 1,000 years.

Evidence of Repeated Evolution

• Multiple Lava Flows:
  • Different genetic mutations led to similar dark fur adaptations on separate lava flows.
  • Indicates evolution can repeat under similar conditions.
• Common Misconception: Evolution is not purely random; natural selection directs advantageous traits' propagation.

Conclusion

• Illustration of Natural Selection: The mice provide a clear example of Darwin’s concept of natural selection.
• Evolution’s Predictability: While mutations are random, the selective process is not, leading to predictable adaptation outcomes.
• Endless Evolutionary Process: As environments change, species must continually adapt, demonstrating evolution’s dynamic and ongoing nature.