Macroevolution

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Macroevolution

• Biology 150-009
• Ms. Chappell
• October 17, 2006

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Species Biodiversity

• How many different species exist?
• Estimates of 4M, 10-15M, and up to 100M
• Only 1.8M species discovered and categorized thus
  far
• If only 4M species now, these 1 of all species
• 99 of species extinct

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Species

• Biological species concept based on breeding
  behavior
• Groups of actually or potentially interbreeding
  natural populations which are reproductively
  isolated from other such groups Ernst Mayr
• Some individuals may cross species line and
  breed, but any offspring hybrid and/or infertile
  (animals in captivity) exception plants

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Speciation

• Development of new species through evolution
• New species may develop through either
• Allopatric speciation (physical separation) OR
• Sympatric speciation
• Either way requires (1) microevolution
  pressure(s) followed by (2) intrinsic, or
  internal, isolating mechanism(s)

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How Speciation Can Occur

• If part of population migrates to new geographic
  area, but members continue interactions/interbreed
  ing, they share microevolution pressures and stay
  same species
• If after physical separation, members do not
  interact/interbreed, populations evolve
  separately. On reintroduction, may not be able
  to breed then two separate species.

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Allopatric Speciation

• Allopatric other country (physical separation)
• Two-stage process of evolution
• First stage geographic separation extrinsic
  (outer) isolating mechanism (that will result in
  different microevolution selection pressures)
• Most important start of speciation but not
  capable of creating evolution alone
• Migration
• Other physical separation by natural or
  human-induced event

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Allopatric Speciation

• Salamander population split around Californias
  Central Valley
• Separate evolutionary histories
• On reintroduction, new species unable to breed
  and create fertile offspring

Fig. 18.2
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Allopatric Speciation

• Second stage an intrinsic (internal) isolating
  mechanism (one of six)
• Six intrinsic reproductive isolating mechanisms
• Ecological isolation (use of habitat)
• Temporal isolation (reproductive timing)
• Behavioral isolation (courtship displays)
• Mechanical isolation (physical mismatch for
  reproduction)
• Gametic isolation (egg/sperm/zygote level)
• Hybrid inviability or infertility (offspring
  level)

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1. Ecological Isolation

• Closely related species with overlapping ranges
  but different or separate habitats (where they
  live, feed, mate, and grow) so rarely meet
• Ex. tigers and lions can mate but dont in
  nature (ligers/tigons)

Top right liger Bottom right tigon Sources
www.scumpa.com and www.nationmaster.com
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2. Temporal Isolation
Rana aurora Jan-Mar
Rana boylii late Mar-May

• Two populations, even if in same habitat, can not
  mate if reproductive schedules differ
• Ex. nocturnal vs. diurnal, early spring vs. late
  spring, etc.

Image source www.bio.miami.edu
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3. Behavioral Isolation

• Even if two populations share habitat and
  reproductive schedule, mating will not occur if
  breeding behaviors out of sync
• Ex. favored courtship dance, correct song range,
  territorial sequestering and defense

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4. Mechanical Isolation

• Reproductive organs incompatible
• If the glove doesnt fit J. Cochran
• Elaborate sex organs of damselflies and
  dragonflies, as well as unique copulation style,
  mechanically isolate species from mating (H.H.
  Ross et al., 1982. A Textbook of Entomology, 4th
  Ed., pp. 290-293) or

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Mechanical Isolation between Plant Species
Source cas.bellarmine.edu/ tietjen/images/speciat
ion.htm
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5. Gametic Isolation

• Some mating occurs between species, but
• Sperm and egg genetically incompatible
• No offspring result
• OR sperm and female reproductive tract
  incompatible
• Plant pollen unable to reach egg
• Animal reproductive tract chemically kills sperm
  or sperm unable to penetrate egg surface membrane

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6. Hybrid Inviability or Infertility

• Assuming two populations share same habitat,
  reproduce on same schedule, share similar mating
  behaviors and compatible reproductive organs, and
  egg and sperm are compatible still isolated
  intrinsically if hybrid offspring are not viable
  (not prone for adaptive survival) or if offspring
  are infertile
• Ex. mule (dad donkey and mom horse)

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Sympatric Speciation

• Sympatric same country
• NO geographic separation
• Same 6 intrinsic isolating mechanisms operating
  within a population to create a new species
• Polyploidy in plants
• Fruit flies on hawthorns and apples
• Hybridization in plants

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Sympatric Speciation Polyploidy

• Genetic accidents create new plant species
• Incompatible chromosomes from different species
  egg and sperm joined
• Chromosomes double without mitotic division
• Next doubling of chromosomes in this zygote
  allows mitosis (for growth) with sister
  chromosomes
• Meiosis possible in new species
• Plants wheat, tobacco, bananas, etc.
• Polyploidy set stage for higher chromosome/
  genetic information found in vertebrates?

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Polyploidy in Wheat

• Different wheat species genetically cross
• Incompatibility of chromosomes solved by gametic
  doubling and non-division (gives each set a
  sister chromosome set)

Figure 18 Essay
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Sympatric Speciation Animals

• NA fruit fly habitat hawthorn tree
• European settlers brought apple trees
• 150 years later, fruit flies with different
  habitats (apples and hawthorns), different
  courting and mating styles, different
  reproductive schedules apple flies and haw
  flies (changed to suit habitat with different
  fruiting schedule)
• 6 interbreed speciation underway

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Sympatric Speciation Hybrids

• Hybrids ? polyploidy
• Similar plants sharing habitat cross pollinate
• Most offspring infertile some however can
  pollinate with one or more of parental species
• High rate of mixing alleles, change
• When hybrid/hybrid fertility occurs, new species

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Sympatric Speciation Hybrids
Iris nelsonii Iris fulva Iris hexagona
Probably result of 3 parental spp.
Fig. 18.6
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When Does Speciation Occur?

• Some species virtually same for millions of years
  (horseshoe crab) while others showed faster
  speciation (13 species of Galapagos finches)
  WHY?
• Generalists vs. specialists
• Of food and environment (generalists more
  immune to natural selection pressures)
• New environments with untapped opportunities
• Adaptive radiation rapid emergence of many
  species from a single species introduced to a new
  environment
• New, unclaimed niches to be filled

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Speciation Transition

• Smooth or jerky creation of new species?
• Darwin assumed gradual change
• Thought complete fossil record, if/when found,
  would bear out truth of gradualism (smooth)
• More complete fossil record indicates jerky
  transition
• Life form in long-term stasis, then quick
  transition (1000s of years, not millions)
• Theory of Punctuated Equilibria

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Comparison of Gradualism and Punctuated Equilibria
Fig. 18.8
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Arguments and Evidence

• Pro-gradualism evolution includes soft parts and
  hard parts only hard parts are in fossil record
• Pro-punctuated equilibria recent supporting
  experimental evidence
• 10K generations of bacteria sudden average
  increase in size
• Change to only 8 genetic loci changed flower
  color etc. and pollinator preferences

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Truth?

• Probably gradualism and punctuated equilibria
  occurring together
• Genetic changes (through mutations) are slow and
  gradual BUT
• Resulting phenotypic changes (as in organism
  morphology its physical form) may be quite
  astounding and relatively fast

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Categories of Organisms

• People like to categorize and classify everything
• Scientists do too choosing to be specific when
  talking about organisms
• Carolus Linnaeus developed taxonomy
• Classification system shows degree of relatedness
  between organisms
• Binomial nomenclature (Genus species) is specific

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Taxonomic System

• Each level taxon
• Kjngdom taxon very diverse, but shared ancestor
  far back in time (here, single-celled protist)
• Genus taxon with close relatives, but not
  interbreeding
• Species taxon actually/ potentially interbreeding
  members of population
• Classifying can be difficult

Fig. 18.9
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Difficulties in Classifications

• When scientists see similarities, must determine
  whether similarities are homologous or analogous
• Homologous means shared ancestry with shared
  morphology
• Analogous means NO recent ancestry (on different
  branches of family tree) so similarities formed
  independently because same function in similar
  environment
• CONVERGENT EVOLUTION

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Homologous vs. Analogous Structures

• Shared ancestry with morphologic similarities
  structures are homologous
• Convergent evolution
• No shared ancestry, but similar morphology
  because of similar function in similar
  environment structures analogous

Fig. 18.11
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How Do Scientists Classify?

• Evolutionary history (phylogeny) devised
• Hypothesis of evolutionary relationships
• Use radiometric dating, fossil record, DNA
  sequencing for degree of relatedness
• Branches of science devising phylogenies
• Classical taxonomy very subjective comparison
  of morphologies (physical forms)
• Systematics use of technologies above
• Cladistics most common approach today

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Cladistics

• Use of shared ancestral characteristics (trunk)
  and derived characteristics (branch) to develop
  cladogram
• All vertebrate animals have shared ancestor with
  vertebrae
• Some vertebrate animals with 4 limbs (tetrapods),
  a derived characteristic unique to that set of
  vertebrate animals

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Cladogram
Physical traits, DNA and RNA sequencing for
similarities, complex calculations used NO
subjectivity
Common ancestor with backbone
Fig. 18.12
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Comparisons between Methods
Birds in own class - Aves
Fig. 18.13
Birds with reptiles