Lecture Notes: Evolutionary Adaptation in Pocket Mice

Introduction

• Location: Valley of Fire, New Mexico
• Landscape: Golden deserts with patches of black volcanic rock
• Historical Context: Volcanic eruptions ~1,000 years ago created a lava flow over 40 miles long

Ecological Setting

• Camouflage and Survival: Evolutionary struggle between visibility and concealment
• Species in Focus: Rock pocket mouse
  • Habitat: Desert sands and dark lava rocks
  • Threats: Predators include foxes, coyotes, rattlesnakes, owls, and hawks

Evolutionary Observations

• Predation and Natural Selection:
  • Light-colored mice blend in with sand but are visible on lava rock
  • Predators drive the color change in mice
  • Dark mice on lava have a selective advantage due to better camouflage

Genetic Basis of Fur Color

• Mutation and Natural Selection:
  • Dark mice originate from mutations, which are rare and random
  • Mutations in the MC1R gene responsible for dark pigmentation
  • Mutations are neither inherently good nor bad; outcomes depend on environmental conditions

Laboratory Findings

• DNA Analysis:
  • Genetic differences between dark and light mice traced to four chemical letters in MC1R gene
  • Mutation gives dark mice an advantage on lava

Speed of Evolution

• Rapid Adaptation:
  • New mutations can spread rapidly
  • Mathematical models show that even a small advantage can lead to significant population changes over time
  • A 5% advantage can lead to a majority dark population in 1,000 years
  • A 10% advantage can achieve this in just 100 years

Broader Implications

• Demonstrating Natural Selection:
  • Simple ecological model with clear selective pressures
  • Genetic basis of adaptation is documented
  • Example of Darwinian natural selection in action

Misconceptions about Evolution

• Evolution is not entirely random:
  • Mutation is random
  • Natural selection is non-random and drives evolutionary change

Repeated Evolutionary Outcomes

• Convergent Evolution:
  • Different populations of rock pocket mice adapt similarly on separate lava flows
  • Different genetic mutations lead to similar phenotypic adaptations
  • Proof that natural selection can produce similar results under similar conditions

Conclusion

• Infinite Evolutionary Process:
  • Environments continuously change, driving species to adapt
  • The rock pocket mice illustrate ongoing evolutionary change and adaptation
  • Evolution repeats itself, adapting life forms to ever-changing conditions