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LECTURE 8: Macroevolution

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Title: LECTURE 8: Macroevolution


1
LECTURE 8Macroevolution
2
What is microevolution?
  • Evolution on a small scale
  • Change in allele frequencies from one generation
    to the next
  • A process that leads to a change in a species
  • Natural selection
  • Genetic Drift
  • Gene Flow
  • Mutation
  • Microevolution explains how populations evolve

3
What is Macroevolution?
  • Origin of different species
  • SPECIATION
  • Extinction of species
  • Evolution of major features

4
What are the Macroevolution Processes?
  • Divergent Evolution
  • Formation of 2 descendent species from an
    ancestral species
  • Homologous structures
  • Convergent Evolution
  • 2 species acquiring same characteristics from 2
    different ancestral species
  • Analogous Structures

5
What is Speciation?
  • Origin of new species

How would we identify if a species is new?
6
How can we see Speciation in the Fossil Record?
7
What are the types of speciation?
  • Coevolution
  • A species evolves due another species evolving
  • Predator/prey relationships
  • Adaptive Radiation
  • Appearance of numerous species over a short
    period of time
  • Filling open niches
  • When would this happen?

8
What is adaptive radiation?
  • Explosion of new species from common ancestor
    that results in diverse species adapted to
    different environments

ADAPTIVE RADIATION
9
What is the tempo of speciation?
  • Punctuated Equilibrium
  • Long periods of little change
  • Occurs after fast/rapid changes
  • Adaptive radiation

PUNCTUATED EQUILIBRIUM
10
Where was there an extinction?
PUNCTUATED EQUILIBRIUM
ADAPTIVE RADIATION
11
What is the Biological Species Concept?
  • Biological
  • Group of individuals capable of interbreeding
  • Is this an accurate definition of a species?

12
  • CASE 1
  • A mule is the offspring of a female horse and a
    male donkey. In contrast, the hinney is the
    offspring of a male horse and female donkey. The
    mule is easier to breed and larger in size than
    the hinney. For these reasons, the mule became
    an important domesticated animal. Horses have 64
    chromosomes, donkeys have 62. The mule has 63
    and cannot evenly divide, that is why the animal
    is sterile.

13
  • CASE 2
  • A liger is a cross between a female tiger and a
    male lion. In contrast, the tigon is a cross
    between a male tiger and a female lion. These
    two species do not breed in nature because their
    habitats are so different. Lions live in open
    grasslands while tigers live in forests. In
    captivity, it is possible to produce ligers and
    tigons. Male ligors are sterile, but female
    ligers are fertile and may reproduce with either
    tigers or lions.

14
  • CASE 4
  • E.coli is a bacterium normally found in the
    intestines. It is harmless and may actually be
    beneficial to the human digestive system. There
    is a pathogenic strain of E.coli that produces a
    toxin that can kill its human host. The two
    strains look very similar under a microscope.
    Comparison of their genomes reveals that the
    pathogenic strain lacks 528 genes found in the
    normal strain and has 1,387 genes not found in
    the normal strain.

15
What are other species concepts?
  • 5 Types
  • Morphological
  • Group of individuals sharing similar
    characteristics
  • Recognition
  • Behavior/chemical recognition between individuals
  • Genetic
  • Range of variation in DNA- similar in individuals
  • Cladistic
  • Species defined as a branch in a cladogram
  • Biological
  • Group of individuals capable of interbreeding

16
Why dont similar species interbreed?
  • Reproductive Isolation
  • Biological barriers preventing members of 2
    species from producing fertile, viable offspring
    hybrids
  • Geographic Isolation

17
What is Geographic Isolation?
  • Geographic Isolation
  • Separation of a species due to obstruction
  • Allopatric Speciation

18
What is Reproductive Isolation?
  • Sympatric Speciation
  • Prezygotic (before fertilization)
  • Timing
  • Diff breeding seasons
  • Behavior
  • Mating rituals
  • Habitats
  • Diff living areas (niches)
  • Mechanical
  • Diff Reproductive Structures
  • Gametic
  • Sperm cannot survive in female reproductive tract
  • Postzygotic (After fertilization)
  • Reduced Hybrid Viability
  • Abort embryonic development
  • Reduced Hybrid Fertility
  • Cannot breed

19
What are the Modes of Speciation?
  • Two general modes of speciation are distinguished
    by the way gene flow among populations is
    initially interrupted
  • Allopatric speciation
  • geographic separation of populations restricts
    gene flow
  • Sympatric speciation
  • speciation occurs in geographically overlapping
    populations when biological factors, such as
    chromosomal changes and nonrandom mating, reduce
    gene flow

20
What is Allopatric Speciation?
  • Geological processes can fragment a population
    into two or more isolated populations
  • Mountain ranges, glaciers, land bridges, or
    splintering of lakes may divide one population
    into isolated groups.
  • Some individuals may colonize a new,
    geographically remote area and become isolated
    from the parent population
  • For example, mainland organisms that colonized
    the Galápagos Islands were isolated from mainland
    populations.

21
What is Allopatric Speciation?
  • Once geographic separation is established, the
    separated gene pools may begin to diverge through
    a number of mechanisms
  • Mutations
  • Sexual selection favors different traits in the
    two populations
  • Different selective pressures in differing
    environments act on the two populations.
  • Genetic drift alters allele frequencies.

22
  • HOW DO WE CONFIRM THAT ALLOPATRIC SPECIATION HAS
    OCCURRED?
  • EXPERIMENT!!!!!

23
What is Sympatric Speciation?
  • New species arise within the range of the parent
    populations
  • Reproductive barriers must evolve between
    sympatric populations
  • In plants, sympatric speciation can result from
    accidents during cell division that result in
    extra sets of chromosomes, a mutant condition
    known as polyploidy
  • In animals, it may result from gene-based shifts
    in habitat or mate preference.

24
IN SUMMARY
  • In allopatric speciation, a new species forms
    while geographically isolated from its parent
    population.
  • As the isolated population accumulates genetic
    differences due to natural selection and genetic
    drift, reproductive isolation from the ancestral
    species may arise as a by-product of the genetic
    change.
  • Such reproductive barriers prevent breeding with
    the parent even if the populations reestablish
    contact.
  • Sympatric speciation requires the emergence of
    some reproductive barrier that isolates a subset
    of the population without geographic separation
    from the parent population.
  • In plants, the most common mechanism is
    hybridization between species or errors in cell
    division that lead to polyploid individuals.
  • In animals, sympatric speciation may occur when a
    subset of the population is reproductively
    isolated by a switch in food source or by sexual
    selection in a polymorphic population.

25
Microevolution or Macroevolution
  • Change in allele frequencies
  • Creation of new species
  • Giraffe necks getting longer
  • A species of birds going extinct
  • A species of beetle have evolved harder shells,
    so a species of bird has evolved beaks that can
    crush the beetles shells
  • -What is this called?
  • There is variation within a snake species, one
    variation survives the other does not survive
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