Lecture Notes: Evolution and Diversity of Anole Lizards

Introduction

• Diversity of animals on Earth is vast, with millions of species.
• Evolutionary biology seeks to understand how such diversity arose.
• Jonathan Losos studies evolutionary processes using Caribbean lizards, specifically anoles.

Anole Lizards in Puerto Rico

• Anoles are divided by habitat:
  • Grass-Bush Anole: Lives in grasses and bushes; slender with long tails.
  • Trunk-Ground Anole: Found on tree trunks and the ground; stockier with longer legs.
  • Twig Anole: Lives on twigs; very small with short legs.
  • Canopy Anole: Larger, green lizard with big toe pads for living high in trees.
• Differences in leg length and toe pad size are adaptations to their specific habitats.

Experiments on Anole Adaptations

• Leg Length Test:
  • Comparison between long-legged ground lizards and short-legged twig lizards.
  • Long legs are advantageous for speed on broad surfaces.
  • Short legs provide a firm grasp on twigs, where long legs are a disadvantage.
• Toe Pad Test:
  • Investigates climbing abilities on slick surfaces like leaves.
  • Larger toe pads help canopy lizards grip surfaces better than ground lizards.
  • Toe pad size is an adaptation to avoid falls from high places.

Observing Evolution

• Hurricanes temporarily clear islands of lizards, providing natural laboratories.
• Introduction of long-legged lizards to treeless islands:
  • Initial introduction of mating pairs.
  • Over generations, lizard legs shortened, showing rapid adaptive evolution.

Speciation and Reproductive Isolation

• Speciation requires reproductive isolation, often through geographical separation.
• Anoles use a dewlap for mating displays, with variations in color leading to speciation.
• Dewlap color changes improve mating success in different environments, contributing to isolation.

Macroevolution and Habitat Differentiation

• Microevolution within populations can lead to macroevolution (formation of new species).
• Competition among species in the same area drives diversification into different habitats.
• Anoles on different Caribbean islands evolved similar body types independently.

Phylogenetic Analysis

• DNA sequencing reveals that lizards on each island are more closely related to each other than to similar lizards on other islands.
• This suggests parallel evolution of similar traits on different islands.

Broader Implications

• The diversity of species is linked to the variety of habitats available.
• Different environments support species with adaptations suited to their specific niches.

Conclusion

• The study of anoles provides insights into evolutionary processes and why there is such a diversity of species globally.
• Environmental diversity leads to numerous survival strategies, fueling the evolution of varied species.