Adaptive Radiations

Page 1: Adaptive Radiations

  • Focus on examples from fish.

  • L2A Theme: "Radiations and Extinctions" by Dr. Kathryn Elmer.

Page 2: Modes of Speciation

  1. Definition of Speciation:

    • Evolution of reproductive isolation within an ancestral species leading to two or more descendant species, characterized by no longer interbreeding in nature.

  2. Geographical Modes of Speciation:

    • Different environments and gene flow potential drive divergence leading to reproductive isolation:

      • Allopatric (vicariant, peripatric)

      • Parapatric

      • Sympatric

  3. Causal Drivers of Speciation:

    • Ecological speciation arises from barriers to gene flow evolving due to ecological divergent selection.

  4. Genetic Modes of Speciation:

    • Involvement of cytoplasmic or genetic incompatibility between diverging populations. Can be slow (genetic drift) or instantaneous (polyploidy).

  • Homework: Example of cytological or recombinational speciation?

Page 3: Adaptive Radiation

  1. Speed of Speciation Factors:

    • Time (neutral evolutionary divergence)

    • Geography (selection for speciation)

    • Lineage effects

  2. Adaptive Radiations:

    • Exemplars of speciation mode and process.

Page 4: Reproductive Isolation

  • Speed to Speciation: A graph showing time to speciation across lineages:

    • 1.0 indicates prezygotic isolation, gradually increasing with time, while postzygotic isolation follows.

  • Genetic Distance (D):

    • Acts as a molecular clock showing the strength of isolation increasing over time.

Page 5: Testing Time to Speciation

  • Allopatric Speciation:

    • Gradual accumulation of prezygotic and postzygotic reproductive isolation as populations diverge.

  • Coyne & Orr:

    • Analyzed Drosophila through numerous experiments; found behavioral prezygotic isolation typically develops fastest.

Page 6: Geography and Speciation

  • Prezygotic Isolation Comparison:

    • Sympatric taxa show earlier prezygotic isolation than allopatric taxa due to reinforcement by natural selection.

Page 7: Biological Speciation Interval (BSI)

  1. Varied Rates of Speciation: Different lineages have distinct rates of speciation.

  2. Bivalve Molluscs, Conifers, Angiosperms: Speciation rates observed within these groups.

  3. Malawi Cichlids: Specific case studies on adaptive radiation showcasing rapid speciation particularly driven by sexual and ecological selection.

Page 8: Process of Speciation

  1. Factors Influencing Time to Speciation:

    • Time, geography, lineage effects.

  2. Adaptive Radiations:

    • Key examples in speciation processes.

Page 9: Understanding Adaptive Radiations

  • Evolution's Processes:

    • Viewed through the lens of adaptive radiation (G.G. Simpson).

Page 10: What are Adaptations?

  • Adaptive Trait: Enhances fitness compared to alternatives.

  • Adaptation/Adaptive Evolution: Changes allowing organisms to survive in environments, involving structural, behavioral, or physiological changes.

Page 11: What are Radiations?

  • High rates of speciation, leading to diverse groups of organisms.

Page 12: Defining Adaptive Radiations

  • Definition:

    • Evolution of ecological and phenotypic diversity within a rapidly multiplying lineage.

  • Example:

    • Adaptive radiation in Galapagos finches with various species adapted to different resources (e.g., seeds, insects).

Page 13: Process of Adaptive Radiation

  1. Phenotypic Differentiation:

    • Caused by environmental differences and resource competition.

  2. Ecological Speciation:

    • Reproductive isolation linked to distinct ecologies enhancing divergence.

Page 14: Testing for Adaptation

  • Comparative Method:

    • Using common-garden experiments, functional morphology, ecological physiology, and reciprocal transplant experiments.

Page 15: How to Test Adaptive Radiations?

  • Comparative Method:

    • Comparison of species sets for hypotheses on adaptations while considering phylogenetics.

Page 16: Common Elements of Adaptive Radiation

  • Criteria:

    • Single common ancestor

    • Colonization of new environments

    • New ecological niches

    • Outcomes of competition

    • Often occurs in "island" habitats.

Page 17: Criteria of Adaptive Radiations

  1. Common ancestry.

  2. Phenotype-environment correlation.

  3. Trait utility.

Page 18: Criteria of Adaptive Radiations Continued

  1. Common ancestry.

  2. Phenotype-environment correlation.

  3. Trait utility.

  4. Rapid speciation observed in unique ecological settings.

Page 19: Cichlid Fish Adaptive Radiations

  • Great Lakes of Africa:


    • 300 species in Lake Victoria and >1000 in Lake Malawi due to ecological niche divergence and sexual selection.

Page 20: Video Resource

  • Cichlids of Lake Malawi:

    • Online video resource link provided.

Page 21: Adaptive Radiations in Crater Lakes

  • Cichlids:

    • Evolution of benthic and limnetic ecomorphs with variations across lakes illustrating adaptive differentiation.

Page 22: Criteria of Adaptive Radiations

  1. Common ancestry.

  2. Rapid speciation processes demonstrated.

Page 23: Genomic Model for Adaptive Radiation

  • Overview of genomic changes contributing to speciation in cichlids.

  • Environmental opportunities and sexual selection lead to significant diversification.

Page 24: Key Points on Adaptive Radiations

  • Common ancestry and rapid speciation are essential.

Page 25: Genomic Evidence

  • Cichlid fish show a unique propensity for diversification rooted in both neutral and adaptive mechanisms of speciation.

Page 26: Summary of Findings

  1. Speeds of speciation depend on time, geography, and lineage effects.

  2. Prezygotic reproductive isolation arises more quickly than postzygotic.

  3. Adaptive Radiations defined by ecological and phenotypic diversity evolution in rapidly multiplying lineages.

  4. Criteria include common ancestry, phenotype-environment correlation, trait utility, and rapid speciation.

  5. Notable adaptive radiations span diverse taxa such as Darwin’s finches and various cichlid species in African lakes.

Page 27: Final Thoughts

  • Encouraging inquiries regarding the mechanisms and outcomes of adaptive radiation and speciation patterns.