BIO1M03 - Week 5 Lecture Notes

Lecture 1 Content:

Phylogenies + History of Life

1. Phylogenetic Trees

  • Phylogeny: Evolutionary history of group of organisms

  • Phylogenetic Tree:

    • Graphical summary of history

    • Evolutionary relationships amogn genes, species, higher taxa

  • Anatomy of a Phylogenetic Tree:

    1. Branch: Population through time

    2. Node (fork): branch splits (most recent common ancestor diverging) = speciation event

    3. Tip (terminal node) endpoint of brant (living/extinct taxon)

    4. Root: ancestral branch in tree

    5. Outgroup: diverged before taxa being studied

    6. Polytomy: node, diverges into 3 or more branches (not enough data)

    7. Extant taxa: Currently living, at tips not nodes (cannot be ancestors)

    8. Sister groups: closely related taxa, share recent common ancestor

  • Data Matrix:

    • Character/trait: genetic/morphological/physiological/behavioural

    • Outgroup = sister group, shares recent common ancestor w/ taza, not part of study group

      • Ancestral: existed in ancestor

      • Derived: modified form of ancestral trait (descendant)

Estimating a Tree (Data)

  • Cladistic Approach:

    • Reconstructing relationships among species based on synapomorphies (shared derived traits)

      • found in 2 or more taxa & most recent common ancestor, missing in distant

    • Monophyletic group: Clades/lineages (ancestral population + all descendants)

      • Can be different based on which trait being studied

  • Complications when Inferring Tree:

    • Similar due to independent evolution - Convergent Evolution

      • Not common ancestry

    • Reversal in Character: creating appeareance that no change occurred

  • Parsimony: Identify most likely tree

    • Least evolutionary change = most likely

  • Homology: Traits similar due to shared ancestry

  • Homoplasy: Traits similar due to reasons outside of common ancestry

  • Convergent Evolution: Common cause of homoplasy

    • Natural selection favours similar solutions to similar environmental pressures

    • Some charateristics may be homologous w/ characteristics in others, some may be convergent

      • Eg. Flowers of Water Lilies

        • phylogenetic evidence (monophyletic group) all lineages have flowers

          • Flowers inherited from common ancestor

          • Structural, genetic, developmental evidence = support plant types homologous

      • Eg. Dolphins and Ichthyosaurs - Homologus or Convergent

        • Phylogenetic analysis - not due to common ancestry

        • CONVERGENT evolution

Lecture 2 Content:

Types of Evidence

  1. Morphological Traits (Phylogeny)

  2. DNA Sequence (Phylogeny)

    • Similarities in sequences (Fewer variations means closer relationship)

  3. Transposeable Elements (SINES - short interspered nuclear elements) - DNA sequences

    • Similarities - closely related

  • Branch Lengths in Phylogenetic Trees:

    • Arbitrary - Cladograms

    • Genetic Difference (scale given)

    • Extent of evolutionary time (Scale given)

2. Fossil Record

Mass Extinctions

  • Rapid extinction of large number of diverse organisms

  • 60% of species wiped out w/in 1 million years

  • opposite of adaptive radiation

  • Background Extinctions: Certain populations reduced to 0

    • Normal environmental change

    • emerging disease

    • predation

    • competition

  • Mass Extinctions:

    • Sudden & temporary changes in environment

    • Exposure to harsh short-tern conditions

End-Permian Extinction

  • Largest mass extinction

  • 90% of all species lost

    1. Siberian traps (flood basalts) - heat, CO2, sulphur dioxide in atmosphere

    2. High atmospheric sulphur dioxide - Severe acid rain (affected plants and fungi)

    3. Flood basalts - widespread coal fires - toxic ash (mercury) in air

    4. Oceans lost oxygen

    5. Sea level dropped dramatically

6th Mass Extinction

  • current

  • habitat loss, pollution, overfishing, invasive species, climate change

  • 1000 higher than background (largest since asteroid)


Lecture 3 Content:

Adaptive Radiation

  • Rapid production, from single lineage, of many descendant species

    • Wide range of adaptive forms

    • sudden appearnce of related diverse species in fossil record (inferred by phylogenetic analysis)

  • 3 Hallmarks of Adaptive Radiation:

    1. Monophyletic Groups

    2. Speciated rapidly

    3. Diversified Ecologically into many niches

  • Niche: Range of resources that a species can use + range of conditions it can tolerate

Why do Adaptive Radiations occur?

  1. Extrinsic Factors: Favourable new conditions in environment

  2. Intrinsic Factors: Evolution of key morphological/physiological/behaviorual traits

Ecological Opportunity

  • Availability of more/new types of resources - driven wide array of adaptive radiations

    • Fewer competators

    • Some can become specialized for growth in different niches

    • mutation, genetic drift, natural selection

      • Eg. Anolis Lizards (Trees vs ground)

Morphological/Physiological/Behavioural Innovation

  • Evolution of key trait —> trigger important diversification events

Escape - Ratiate Coevolution Hypothesis

  • Reciprocal evolutionary change in interacting species

    • adaptations w/in lineages

      • Defense mechanisms in plants vs counter defence traits in insects

    • Coevolution between insect herbivores and plants

      • Plants (mutation and recombination) evolved chemical compounds as defence mechanism against herbivory

        • Escape - inesct herbivores - higher relative fitness than plants lacking defense mechanism

      • Insect herbivores evolved counteradaptations to feed on plants w/ defense mechanism

    • Resulted in increased diversification rates

Cambrian Explosion

  • When life diversified from unicellular to multicellular - more “complex” organisms

    • Diversification - Most significant evolutionary change in history

    • first animals 635 million years ago —> 50 million years later, animals larger more complex

    • Fossil evidence (Canada, China, Australia)

    • Fauna: Fossil assemblace records distinctive collection of animal species

Trigger for Cambrian Explosion

  1. Higher oxygen levels

  2. Evolution of Predation

  3. New niches beget more new niches (ecological opportunity)

  4. New genes, new bodies

    • HOX genes (genes that code/instruct for more complex traits)

Early Animal Fossils

  • Microfossils from Edicaran Period

    • First animals to appear (super small sponges and corals)

    • Macroscopic fossils during Edicaran

      • Sponges, jellyfish, comb jellies, etc

      • No shells, imbs, heads, feeding appendages, etc

      • Burrowing, floating, immobile filter feeders

  • Cambrian macroscopic fossils

    • Sponges, jelly fish, comb jellies, etc

    • Swam, burrowed, walked/ran, slithered, clung or floated

    • Predators, scavengers, filter feeders, grazers

    • Ecological niches in marine habitats


Burgess Shale - Cambrian Explosion

  • Fossilized evidence from area — suggests evidence for Cambrian Explosion