Lecture 1: Lizard Evolution (BIOL 214) — Notes on Lizards in an Evolutionary Tree Ecomorphs

Course Context and Goals

  • Course: BIOL 214 – Genes, Ecology & Evolution (Fall 2025)

  • Schedule: Tuesday/Thursday, Section 101

  • Instructional team (from transcript): Drs. Nancy DiIulio and Fritz Petersen (Instructors); Isabela Darling, Isabelle Todd, and Joe Terry (Graduate TAs); Misha Panchal and Emily Zhang (Supplemental Instructors)

  • Text/Resources cited in transcript: The Dynamic Science by Russell, Hertz, and McMillan (Cengage Learning); Course Canvas page

  • Purpose: Develop understanding of both the diversity and unity of life on Earth

  • Related online resources mentioned:

    • General concept resource: http://palaeos.com/systematics/tree/

    • Anole evolution resource (video/classroom): https://www.biointeractive.org/classroom-resources/origin-species-lizards-evolutionary-tree

Core Concepts: Diversity, Unity, and Evolutionary Framework

  • Genes, Evolution, and Ecology aim to explain how life varies and why there is a unity of life across the planet

  • Emphasis on evolutionary mechanisms that generate biodiversity while conserving underlying biological principles

  • Contextual link to Darwinian theory: foundational ideas about descent with modification and adaptive change over time

Case Study Introduction: Lizards in an Evolutionary Tree

  • Real-world example used to illustrate how evolutionary processes produce diversity in a connected, hierarchical fashion

  • Organisms studied: Anole lizards on Caribbean islands (Cuba, Hispaniola, Jamaica, Puerto Rico) as a model system for adaptive radiations

  • Visual cue: The documentary/figure set outlines how closely related populations diverge to fill different ecological niches

  • Key takeaway: Similar ecological roles (habitats) arise repeatedly in separate populations due to similar selective pressures, showing both convergence and lineage-specific diversification

Anoles on Caribbean Islands: Ecological Niches and Ecomorphs

  • Concept: Ecomorphs are groups defined by a combination of body form and habitat use, reflecting adaptation to specific ecological niches

  • Ecological niches depicted: high canopy, trunks and branches, narrow twigs, lower trunk and ground, grass/bush environments

  • Visual evidence: Six distinct ecomorphs are described with consistent habitat associations across the Caribbean islands

Table 1: Six Ecomorphs of Anole Lizards Found on the Caribbean Islands

  • Ecomorph: Crown-giant

    • Body length: 130-191 ext{ mm}

    • Limb length: short

    • Toe pad lamellae: Large

    • Tail length: Long

    • Color: Usually green

    • Habitat: High trunks and branches

  • Ecomorph: Trunk-crown

    • Body length: 44-84 ext{ mm}

    • Limb length: short

    • Toe pad lamellae: Very Large

    • Tail length: Long

    • Color: Green

    • Habitat: Trunks, branches, leaves

  • Ecomorph: Trunk

    • Body length: 40-58 ext{ mm}

    • Limb length: Intermediate

    • Toe pad lamellae: Intermediate

    • Tail length: Short

    • Color: Gray

    • Habitat: Trunks

  • Ecomorph: Twig

    • Body length: 41-80 ext{ mm}

    • Limb length: Very short

    • Toe pad lamellae: Small

    • Tail length: Short

    • Color: Gray

    • Habitat: Narrow twigs

  • Ecomorph: Trunk-ground

    • Body length: 55-79 ext{ mm}

    • Limb length: Long

    • Toe pad lamellae: Intermediate

    • Tail length: Long

    • Color: Brown

    • Habitat: Lower trunk and ground

  • Ecomorph: Grass-bush

    • Body length: 33-51 ext{ mm}

    • Limb length: Long

    • Toe pad lamellae: Intermediate

    • Tail length: Very Long

    • Color: Brown

    • Habitat: Bush and grasses

Figure and Conceptual Implication: Ecological Niches Drive Adaptive Differentiation

  • Figure 3 (caption paraphrase): Anoles occupy diverse ecological niches and have evolved adaptations enabling success in different microhabitats (e.g., different parts of trees, grasses, and bushes)

  • Conclusion from the figure: Six ecomorphs correspond to different ecological niches in the Caribbean islands, illustrating adaptive differentiation despite shared ancestry

Observations of Two Anole Species: Data and Inquiry (Species A vs Species B)

  • Species A:

    • Habitat: High Trunks and branches

    • Body length: 130-191 ext{ mm}

    • Limb length: Short

    • Toe-pad size: Large

    • Tail length: Long

    • Color: Green

  • Species B:

    • Habitat: Lower trunk and ground

    • Body length: 55-79 ext{ mm}

    • Limb length: Long

    • Toe-pad size: Intermediate

    • Tail length: Long

    • Color: Brown

  • Discussion prompts for students:
    1) Describe the differences between the two species
    2) Formulate hypotheses explaining why each difference may have evolved
    3) Propose an experiment to test one of the hypotheses

Experimental Approach: How Did Ecomorph Diversity Arise?

  • Experimental setup used by Losos and team: nearby Caribbean islands served as natural laboratories

  • Island conditions: Islands largely free of Anoles after hurricanes removed lizards; a small number of Anoles were left behind on some islands

  • Experimental design: Revisit islands one year later to observe recolonization and potential rapid adaptation to available habitats

  • Core idea: Test whether new populations will diverge in body form and habitat use in response to novel ecological opportunities

The Results: Habitat, Distribution, and Inference

  • On different islands, the six ecomorphs appear in various combinations and occupy corresponding habitats

  • Example mapping (selected from transcript data):

    • Twig: Puerto Rico; also observed in Cuba, Hispaniola, Jamaica across multiple habitats

    • Canopy: Puerto Rico; Canopy in Cuba, Hispaniola, Jamaica

    • Grass: Puerto Rico; Grass in Cuba, Hispaniola, Jamaica

  • Overall inference: The appearance of similar ecomorphs on different islands implies repeated evolution of similar body types in response to analogous ecological pressures

Phylogenetic Interpretations: Reading the Figure (Left vs Right Trees)

  • The transcript presents a set of paired statements for interpretation of phylogenetic trees (Figure with left and right trees) and asks students to select which pairs accurately describe the trees

  • The options describe different scenarios:

    • A: Twig lizard as the ancestor across islands, with canopy and grass lizards evolving from twig lizard

    • B: Body types evolved repeatedly and independently on each island; the same body type ends up on different islands

    • C: Body types evolved only once, with populations spreading to different islands; there are two ancestors (twig and canopy lizards) to all lizards

    • D: Puerto Rico as the origin for all three body types, with independent repeated evolution on each island

  • Note: This section encourages careful reading of phylogenetic patterns and understanding of concepts like shared ancestry, monophyly, and repeated evolution

The Results (Revisited): Most Likely Hypothesis for Evolutionary Pathways

  • Question prompts: Which tree most plausibly represents how the Caribbean anole species evolved? Students are asked to explain their reasoning

  • Core takeaway: The data support adaptive radiations within islands, with close relatedness among island populations and repeated, convergent evolution of similar ecomorphs across islands

Conclusions: Key Takeaways about Island Biogeography and Evolutionary Patterns

  • Main conclusion: Lizards on each island are more closely related to each other than to similar lizards on other islands, indicating island-specific diversification

  • Implication: The same types of lizards evolved independently on different islands due to similar ecological opportunities and selective pressures (parallel/parallel adaptive radiations)

  • This case study illustrates the broader pattern of biodiversity arising from layered, interacting processes over time

Broader Context: Darwin, Biodiversity, and Course Emphasis

  • The materials connect to Darwin’s legacy: descent with modification and adaptive change across lineages

  • BIOL 214 aims to review and build on Darwin’s framework to deepen understanding of how processes and interactions generate the unity and diversity of life on Earth

  • Real-world relevance: Understanding speciation, adaptive radiations, and ecological niches informs conservation, ecology, and evolutionary biology

Connections to Foundational Principles and Real-World Relevance

  • Conceptual links:

    • Evolution by natural selection explains how environmental pressures shape form and function

    • Adaptive radiations show how rapid diversification can occur in response to newly available ecological space

    • Convergent evolution can produce similar forms in distinct lineages facing similar niches

  • Real-world relevance:

    • Island biogeography studies inform biodiversity management and conservation strategies

    • The anole model demonstrates how microhabitats influence morphology and behavior, with implications for understanding speciation and ecological resilience

Formulas, Numbers, and Key References (LaTeX-formatted)

  • Ecomorph body length ranges (examples):

    • Crown-giant: 130-191\ \mathrm{mm}

    • Trunk-crown: 44-84\ \mathrm{mm}

    • Trunk: 40-58\ \mathrm{mm}

    • Twig: 41-80\ \mathrm{mm}

    • Trunk-ground: 55-79\ \mathrm{mm}

    • Grass-bush: 33-51\ \mathrm{mm}

  • Habitat categories (textual): High Trunks and branches; Trunks, branches, leaves; Trunks; Narrow twigs; Lower trunk and ground; Bush and grasses

Additional References and Resources

  • General evolution and systematics resource: http://palaeos.com/systematics/tree/

  • Anole evolution classroom resource: https://www.biointeractive.org/classroom-resources/origin-species-lizards-evolutionary-tree

  • These resources provide visuals and supplementary context for the observed patterns and interpretations discussed in BIOL 214