Lecture Notes: The Diversity and Evolution of Anoles in the Caribbean

Introduction

• Millions of species adapted to various habitats.
• Evolution of species is a major quest in biology, highlighted by Darwin's work.
• Focus on a specific study by Jonathan Lossus on Caribbean lizards.

Overview of Anoles in Puerto Rico

• Jonathan is studying lizards called anoles.
• Uses clues from their bodies, lifestyles, and DNA to understand origins and species formation.
• Anoles in Puerto Rico are divided by habitat:
  • Grass Bush Anole: Long-tailed, slender, lives in grasses and bushes.
  • Trunk-Ground Anole: Stockier, lives on tree trunks and the ground.
  • Twig Anole: Small, short-legged, lives on twigs and branches.
  • Canopy Anole: Large, green with big toe pads, lives high in the canopy.

Habitat and Adaptations

• Each species occupies a different vertical space, analogous to apartment dwellers.
• Differences in leg length and toe pad size indicate adaptations to their habitats:
  • Long-legged lizards (e.g., ground lizards) are faster on broad surfaces.
  • Short-legged lizards (e.g., twig lizards) excel at balancing on thin branches.

Experiments Conducted

• Jonathan conducts experiments comparing running ability and climbing on various surfaces.
  • Running Ability: Long legs advantageous on broad surfaces for ground lizards; short legs beneficial for twig lizards on narrow surfaces.
  • Climbing Ability: Different sized toe pads impact the lizards' ability to climb slick leaves.
  • The larger canopy lizard uses microscopic hairs on toe pads to grip surfaces effectively.

Evolutionary Studies

• Jonathan's team experiments with lizards on hurricane-depleted islands:
  • Captured tree-dwelling anoles and introduced them to cleared islands.
  • Observed that the populations adapted over generations, developing shorter legs for navigating thin branches.
  • Evolution can occur rapidly under strong natural selection.

Speciation and Reproductive Isolation

• New species arise when populations are reproductively isolated:
  • Isolation can happen geographically or due to changes in traits (e.g., dewlap color in males).
  • Dewlap differences help prevent interbreeding between different populations.

Insights on Evolution

• Connection between microevolution (changes within populations) and macroevolution (formation of new species).
• Competition among species for resources leads to diversity in body types:
  • Similar body types of anoles observed across Caribbean islands (e.g., Puerto Rico, Jamaica, Cuba, Hispaniola).
• DNA sequencing shows that similar traits evolved independently on each island.

Conclusion

• The abundance of species is linked to the variety of habitats.
• Each habitat provides unique survival strategies, contributing to biodiversity:
  • Example of resource partitioning in the Serengeti (zebras, wildebeest, Thompson's gazelles).
  • Different environments host various creatures, each adapted to their specific niche.