Lecture Notes: Evolution of Rock Pocket Mice in the Valley of Fire

Introduction

• Location: New Mexico's Valley of Fire
  • Southwestern desert landscape interrupted by black volcanic rocks
  • Volcanic eruptions ~1,000 years ago created a 40-mile lava flow

Evolutionary Context

• Camouflage and Predation
  • Rock pocket mouse: light-colored fur blends with desert sands
  • On dark lava rocks, light fur makes them vulnerable to predators
  • Predators include foxes, coyotes, rattlesnakes, owls, and hawks

Adaptation of Rock Pocket Mice

• Biologist Michael Nachman's Findings
  • Dark mice evolved to blend in with black rocks
  • White underbelly remains due to no selection pressure from above
  • Predators drive color change by weeding out poorly camouflaged mice

Genetic Basis of Dark Fur

• Mutation and Natural Selection
  • Dark mice arise from rare genetic mutations
  • Mutations are random but selection is non-random
  • Effectiveness of mutation depends on environmental conditions

Laboratory Research

• DNA Analysis by Nachman’s Team
  • Goal: Identify mutations causing dark coloration
  • Found differences in four chemical letters of the MC1R gene
  • MC1R gene controls dark pigment production

Spread of Dark Fur Mutation

• Rapid Evolutionary Change
  • Despite being a recent lava flow (~1,000 years), dark mice prevail
  • Minimal advantage (e.g., 5%) can quickly dominate population
  • Mathematical modeling confirms rapid spread of advantageous traits

Illustration of Natural Selection

• Example of Natural Selection
  • Simple ecological system: dark rocks, light rocks, dark mice, light mice
  • Clear identification of predators and selective forces
  • Demonstrates Darwin’s process of natural selection

Misconceptions About Evolution

• Random vs. Non-random
  • Mutation is random; natural selection is not
  • Selection determines survival based on advantageous traits

Repeated Evolution Across Regions

• Comparison of Lava Flows
  • Different genetic mutations in separate lava regions result in similar dark mice
  • Similar conditions favor similar adaptations
  • Demonstrates evolution can repeat itself in different settings

Conclusion

• Ongoing Evolutionary Change
  • Evolution is a constant adaptive process
  • As environments change, species must adapt to survive
  • Demonstrates the dynamic nature of evolutionary processes