Organismal Biology, Ecology, and Evolution

Evolution: Biology’s Unifying Framework

  • Importance of evolution in explaining biological diversity

  • Evolutionary processes occur over time

  • Relevance of evolution in organismal biology

  • Understanding organismal traits requires an evolutionary context

  • Evolution serves as the link between:

    • Form

    • Function

    • Diversity

    • Ecology

Case Study: Anole Lizards

  • Genus Anolis:

    • Native to the Americas

    • Taxonomic variance: between 45 and 425 species identified

    • Characteristics: small, mainly insectivorous, color-changing for camouflage or mood

    • Males exhibit a dewlap for attracting mates or deterring rivals

Tree of Life

  • Organisms are classified into three domains:

    • Bacteria

    • Archaea (first proposed in the 1970s by Carl Woese through ribosomal RNA gene analysis)

    • Eukarya which includes:

    • Protists

    • Fungi

    • Plants

    • Animals

Defining Evolution

  • Evolution Defined:

    • Result of random mutations

    • Change in heritable traits over generations

    • Change in the allele frequency in populations over time

    • Key Terms:

    • Population: Group of members from the same species within a geographic location

    • Example of a species:

    • Species: Panthera tigris

    • Classification:

      • Genus: Panthera

      • Family: Felidae

      • Order: Carnivora

      • Class: Mammalia

      • Phylum: Chordata

      • Kingdom: Animalia

What is a Species?

  • Observations:

    • Similarities among individuals within a species

    • Offspring resemble their parents closely

  • Historical Definition:

    • Developed by Carolus Linnaeus (1700s), based on visual similarities

  • Modern Definition:

    • Biological Species Concept (BSC): Organisms that interbreed and produce fertile offspring constitute the same species

    • Note: BSC limitations in certain groups (e.g., Anolis carolinensis & Anolis porcatus)

Clarification on Evolution

  • What Evolution Is:

    • Change in heritable characteristics across generations

    • Involves allele frequency changes in populations over time

  • What Evolution Isn’t:

    • Local changes in individuals

    • A linear process, as it branches in many directions

    • A constant path of improvement or forward progression

Avoiding Teleological Thinking

  • Teleology: The belief that evolution has a defined purpose or goal

    • Example: An acorn evolving to become an oak tree

    • Misconception: Organismal ancestors “wanted” certain traits to evolve

    • Important to recognize and avoid teleological thinking in this course

Mechanisms of Evolution: Natural Selection

  • Natural Selection: Key evolutionary mechanism characterized by the following conditions (4 Pillars):

    • Variation exists within nature

    • Heritability of some variations

    • Overproduction leads to competition for resources

    • Favorable adaptations are naturally selected for survival and reproduction

Natural Selection in Action: Case Studies

  • Brown Anole (Anolis sagrei):

    • Rapid evolutionary adaptations for better grip during strong winds, as observed after hurricanes Irma and Maria (2017)

    • Data showed surviving lizards had:

    • Larger toepads

    • Longer front limbs

    • Shorter hind limbs

    • Pass on advantageous traits to subsequent generations

Evidence for Evolution

  • Clues from history indicate all organisms are derived from a common ancestor

  • Evidence types showing how species are related:

    • Life arose approximately 3.8 billion years ago

    • Adaptations accumulate over time leading to today's diversity

Adaptations

  • Definition: Heritable changes that enhance survival and reproductive success

    • Adaptations enhance fitness

  • Example: Four phenotypes of Bahamian Anolis lizards based on ecology:

    • Crown specialist (e.g., A. equestris):

    • Characteristics: Large body, short legs, large toepads

    • Trunk-crown specialist (e.g., A. carolinensis):

    • Characteristics: Short legs, large toepads, long head

    • Trunk specialist (e.g., A. distichus):

    • Characteristics: Small body, medium legs, short head

    • Trunk-ground specialist (e.g., A. sagrei):

    • Characteristics: Large body, small toepads, medium head

How Adaptations Arise

  • Random mutations introduce new traits

  • Individuals with beneficial traits are more likely to survive and reproduce

    • These advantageous traits increase in population frequency over generations

    • Over time, organisms become well-adapted to their environments

  • Types of adaptations:

    • Structural: Physical features

    • Behavioral: Actions taken by organisms

    • Physiological: Internal processes

Evidence from the Fossil Record

  • Fossils: Imprints or remains of past organisms; provide critical evidence for evolution

  • Paleontology: Study of fossil remains to understand past life

  • Importance of fossils in showing relationships among organisms over time

Types of Fossil Evidence: Body Fossils

  • Include various body parts: pollen, leaves, flowers, seeds, bones, teeth, shells, fur

  • Fossilization methods include:

    • Permineralization: Minerals replace organic material

    • Entombing: Preserved in amber or resins

    • Mummification: Dehydration without decay possible in cold or dry environments

    • Preservation in specific conditions: Tar pits and peat bogs

Fossil Formation Process

  • Sequence:

    • Organism leaves footprints or dies, flesh rots, bones remain

    • Erosion exposes bones, sediment buries the remains

    • Accumulation of sediments results in fossilization

Types of Fossil Evidence: Trace Fossils

  • Evidence indicating biological activity includes:

    • Tracks

    • Eggshells

    • Waste materials (coprolites)

Analyzing Fossil Evidence

  • The stratigraphy of rock layers reveals the relative age of fossils

  • Relative dating: Assumes lower layers are older than upper layers; shows the order of organism occurrence without providing exact dates

Understanding Fossil Ages

  • Relative Dating: Infers age based on the layer depth

  • Examples of ages discussed include:

    • 40,000 years

    • 100 million years

    • 500 million years

    • 67 million years

    • 45 million years

Absolute Dating Techniques

  • Provides exact dates of occurrence using radiometric dating

  • Key Concepts:

    • Radioactive elements undergo decay at known rates

    • The half-life concept is essential to determine ages of substances

Carbon-14 Dating

  • Carbon-14 Dating:

    • Living organisms maintain a balance of C-14

    • After death, C-14 intake ceases but decay continues

    • Example:

    • Half-life of C-14 = ~5,700 years

    • Proportional decay allows for dating

Limitations of Carbon Dating

  • Only effective for dating objects less than approximately 50,000 years old

  • Not applicable for dating dinosaur fossils (which are older)

  • Alternative isotopes like Uranium and Potassium have longer half-lives (>1 million years) but were not present in dinosaur remains; igneous rocks or volcanic ash dated instead

Transitional Fossils

  • Provide evidence supporting relationships between different species

    • Example:

    • Whales' descent from four-legged land animals

    • Relatedness of birds and certain dinosaurs

    • Insights into human evolution

    • Evolution of horses

    • Example of horse evolution over time includes:

    • Mesohippus: 35 MYA

    • Pliohippus: 8 MYA

    • Merychippus: 15 MYA

    • Equus: 5 MYA to present

Insights on the Fossil Record

  • Fossil record is incomplete due to factors:

    • Certain organisms (e.g., soft-bodied) do not fossilize well

    • Erosion and geological activity may destroy fossils

    • Not all fossils formed will be discovered

  • Biased towards organisms that were:

    • Abundant and long-lived

    • Had hard skeletons or shells

Biogeography

  • Definition: The study of distribution of species across geographical areas

  • Earth's geography has significantly changed over the past 200 million years due to plate tectonics

  • The geographic distribution of species suggests evolution from common ancestral forms

Historical Geography and Biogeography

  • Fossils contribute to the reconstruction of Earth's continents, historically linked as Pangaea

Wallace’s Line

  • Animals separated by Wallace’s Line have evolved independently for millions of years

  • Results in unique biodiversity on either side of the line

Biogeographical Examples

  • Some evolutionary aspects of biogeography make sense only through evolutionary perspectives, such as those of marsupials in Australia and Anole lizards

Comparative Anatomy

  • Study of anatomical or morphological features elucidates evolutionary relationships among species

  • Structures classified as:

    • Homologous: Similarities resulting from a shared ancestor

    • Analogous: Similarities due to convergent evolution

Homologous vs. Analogous Structures

  • Homologous Structures:

    • e.g., forelimbs of mammals indicating common ancestry

    • Changes result from selective pressure rather than new designs

  • Analogous Structures:

    • Evolved independently yet share similar functions due to environmental pressures

Vestigial Structures

  • Definition: Structures that have lost their original function but are homologous to functional structures in other species

  • Examples: Hind limbs in certain snakes; pelvic bones in whales

Convergent Evolution

  • Refers to similar morphologies in unrelated organisms due to similar selective pressures

  • Example:

    • Parallel evolution of marsupial and placental mammals

More Examples of Convergent Evolution

  • Specific examples of convergence highlight adaptations among animals:

    • Marsupial mole and placental moles, flying squirrels (marsupial vs. placental)

Comparative Embryology

  • Early development stages across species reveal homologous structures

    • Commonality in embryos suggests shared ancestry

  • Strong morphological similarities in embryonic stages between humans and other species

Insights from Molecular Biology

  • Comparison of DNA sequences provides detailed insights into evolutionary relationships

    • Genes and proteins are essential to hereditary information

    • Unlikely identical DNA sequences arise in unrelated species by chance; more probable they stem from a shared ancestor

Molecular Clock Concept

  • Assumption of Constant Mutation Rates:

    • Mutations accumulate at a steady rate, allowing estimation of divergence time

  • Method of measuring genetic mutations over time to infer evolutionary timelines across species

Example of Molecular Clock Application

  • Mitochondrial Protein: Cytochrome c is often used for molecular comparisons

    • More amino acid differences indicate a more distant common ancestor

Conclusion on Evolution

  • An organism's adaptations are the outcomes of evolution.

  • Key Themes:

    • Evolutionary links explain unity and diversity among living organisms

    • Shared traits arise from common ancestry, while diversity results from heritable changes over time.