Lecture

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Lecture 3 Origin of Species
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Key Concepts

• Species concepts
• Development of reproductive isolation
• Patterns of speciation
• Macroevolution
• Human evolution
• Evolution continues..

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My pet peeve is.
Species is both singular and plural
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Major Species Concepts

• Biological
• Morphological
• Phylogenetic

Diagram variation in beaks between species
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Biological species the basic standard for
separating species (Ernst Mayr, 1942)

• Species are defined by natural reproductive
  isolation
• Individuals that can produce successful offspring
  are considered the same species

Image Sarracenia rubra
Image Sarracenia flava
?
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Critical Thinking

• Biological species are defined by natural
  reproductive isolation
• Individuals that can produce successful offspring
  are considered the same species
• Definition doesn't always work why not???

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Critical Thinking

• Biological species are defined by natural
  reproductive isolation
• Individuals that can produce successful offspring
  are considered the same species
• Definition doesn't always work

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Morphological species the first way to separate
species (Linnaeus, 1750 others)

• Species are defined by differences in form
• Individuals with the same morphology and/or
  anatomy are considered the same species

Image Hymenocallis floridana
Image Hymenocallis coronaria
?
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Critical Thinking

• Morphological species are defined by differences
  in form
• Individuals with the same morphology and/or
  anatomy are considered the same species
• Definition doesn't always work why not???

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Critical Thinking

• Morphological species are defined by differences
  in form
• Individuals with the same morphology and/or
  anatomy are considered the same species
• Definition doesn't always work

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Phylogenetic species the new standard for
separating species???

• Species are defined based on evolutionary history
  
• Species defined by the smallest monophyletic
  group in an evolutionary tree
• Monophyletic lineage is derived from a common
  ancestor
• Definition doesn't always work
• Dont have good phylogenies for all species or
  groups
• Also, imperfect agreement on interpretations

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Development And Maintenance Of Reproductive
Isolation
It is generally accepted that natural
reproductive isolation defines and preserves
separate species in sexually reproducing organisms

• What constitutes a barrier to reproduction?
• How do reproductive barriers develop?

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Pre-zygotic Barriers

• Remember, the zygote is the fertilized egg cell
• The first cell of the new offspring
• Pre-zygotic barriers prevent the formation of the
  zygote
• Natural, evolved incompatibilities prevent
  successful fertilization
• Habitat isolation
• Behavioral isolation
• Temporal isolation
• Structural isolation
• Chemical isolation

Image blue-footed boobies mating behavior
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Critical Thinking

• Natural, evolved incompatibilities prevent
  successful fertilization
• Think of some examples of
• Habitat isolation
• Behavioral isolation
• Temporal isolation
• Structural isolation
• Chemical isolation

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Critical Thinking

• Habitat isolation
• Behavioral isolation
• Temporal isolation
• Structural isolation
• Chemical isolation

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Post-zygotic Barriers

• Post-zygotic barriers prevent successful
  development of offspring
• Hybrids dont develop properly
• Hybrids dont reach sexual maturity
• Hybrids dont produce viable gametes
• Hybrid lineages fail over time
• Natural genetic incompatibilities prevent
  successful long-term reproduction

Horse x Donkey robust but sterile Mule
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Critical Thinking
The Darwinian fitness of an individual is
measured by

• its ability to reproduce.
• how long it lives.
• the number of mates it attracts.
• the number of its offspring that survive to
  reproduce.
• its physical strength.

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Critical Thinking
The Darwinian fitness of an individual is
measured by

• its ability to reproduce.
• how long it lives.
• the number of mates it attracts.
• the number of its offspring that survive to
  reproduce.
• its physical strength.

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Patterns of SpeciationBarriers result from
separations that persist long enough that
eventually new species have developed
Diagram different species of fish in separated
ponds
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Patterns of Speciation

• Pattern depends on the mechanism of gene flow
  interruption
• Allopatric speciation occurs when populations are
  separated by a geographical barrier
• Sympatric speciation occurs in the absence of a
  geographic barrier

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Critical Thinking

• Allopatric speciation occurs when populations are
  separated by a geographical barrier
• Such as????
• How could such barriers form???

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Critical Thinking

• Allopatric speciation occurs when populations are
  separated by a geographical barrier
• How could such barriers form???

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Critical Thinking

• Allopatric speciation occurs when populations are
  separated by a geographical barrier
• How could such barriers form???

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Critical Thinking
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Allopatric Speciation

• Once populations are physically isolated,
  speciation may occur due to all the evolutionary
  processes we talked about earlier
• Selection
• Drift
• Selective mating
• Mutation

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Critical Thinking

• What if the isolated population is small???
• What if the isolated population is from edge of
  the range of the original population???

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Critical Thinking

• What if the isolated population is small???
• What if the isolated population is from edge of
  the range of the original population???

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Critical Thinking

• What if the isolated population is small???
• What if the isolated population is from edge of
  the range of the original population???

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Allopatric Speciation due to geographic separation
Plants????
Birds???
Images different species of chipmunk on either
side of the Grand Canyon
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Speciation may, or may not, occur
Diagram sympatric ? allopatric ? either
sympatric again or not.
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Sympatric Speciation

• Occurs when a population becomes reproductively
  isolated without geographic barriers
• Mutations or selection pressures that lead to
  changes in behavior, habitat, food source,
  phenology.
• Errors in meiosis that lead to polyploidy (some
  plants can be self-fertile, vegetative
  reproduction)
• Hybrids that develop into fertile populations
  through vegetative reproduction (mostly plants)

Diagram sympatric speciation in a forest
environment
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Sympatric Speciation

• Occurs when a population becomes reproductively
  isolated without geographic barriers
• Mutations or selection pressures that lead to
  changes in behavior, habitat, food source,
  phenology.
• Errors in meiosis that lead to polyploidy (mostly
  plants)
• Hybrids that develop into fertile populations
  through vegetative reproduction (mostly plants)

Diagram meiosis errors
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Polyploidy one mechanism for sympatric
speciation
Diagram errors in meiosis can lead to polyploids
Some plants can be self-fertile, or vegetative
reproduction can produce multiple fertile
individuals
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Sympatric Speciation

• Occurs when a population becomes reproductively
  isolated without geographic barriers
• Mutations or selection pressures that lead to
  changes in behavior, habitat, food source,
  phenology.
• Errors in meiosis that lead to polyploidy (some
  plants can be self-fertile, vegetative
  reproduction)
• Hybrids that develop into fertile populations
  through vegetative reproduction (mostly plants)

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Speciation is NOT a Given

• Must have an interruption to gene flow
• PLUS
• Must have enough change in the separated
  populations to provide a barrier to reproduction

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Endemic Species and Adaptive Radiation

• Endemic species restricted in distribution to a
  particular place, generally because they evolved
  in place
• Volcanic island chains often contain many endemic
  species
• No biota until they were colonized by a few
  individuals (founder effect)
• These small populations then evolved into new
  species
• Allopatric speciation due to the geographic
  barrier from the founder effect
• But also

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Endemic Species and Adaptive Radiation

• Many new species develop that are adapted to the
  diverse new habitats found in such islands
• Sympatric speciation
• No geographic barriers
• Adaptive radiation into new habitats

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Adaptive Radiation
Galapagos finches and Hawaiian honeycreepers
Diagrams adaptive radiation in birds
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Adaptive Radiation is a common theme both
between and within lineages
Diagram mass extinctions over the past 2.5
billion years
Diagram diversification of mammals after
extinction of the dinosaurs
Mass Extinction Events
Mammals
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Critical Thinking

• Humans have initiated a mass extinction event
• Will life cease to exist on the planet???
• Can we destroy the planet???

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Critical Thinking

• Humans have initiated a mass extinction event
• Will life cease to exist on the planet???
• Can we destroy the planet???

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Critical Thinking

• Humans have initiated a mass extinction event
• Will life cease to exist on the planet???
• Can we destroy the planet???

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Speciation is a Constant

• When migration, isolation or other selection
  pressures force divergence, reproductive
  isolation can eventually lead to speciation
• Speciation might be gradual or abrupt (punctuated
  equilibrium)
• Transitions (either gradual or abrupt) may or may
  not be captured in the fossil record

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Macroevolution larger-scale changes in
organismsAlso contributes to speciation

• Small, population-scale changes can accumulate
• Exaptations traits can be co-opted
• Feathers for thermoregulation ? feathers for
  flight
• Large phenotypic changes can result from small
  changes in regulatory genes
• Control over the timing and length of
  developmental events, or the spatial organization
  of body parts

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Critical Thinking
Was the evolution of the modern horse a series of
directed events ????
Diagram phylogeny of the modern horse
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Critical Thinking
Was the evolution of the modern horse a series of
directed events???
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Selection is a series of gates!!!
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A Preview of the Taxonomic Hierarchythis is how
we classify diversity
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Images the yellow fringed orchid
Platanthera ciliaris
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Humans can also be classified!

• Domain eukarya
• Kingdom animal
• Phylum chordates
• Sub-phylum vertebrates
• Class mammals
• Order primates
• Family hominoids
• Genus Homo
• Specific epithet sapiens

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Phyla in the Animal Kingdom
Diagram from this slide to slide 65
phylogenies of the animal kingdom, showing the
classification of humans through the taxonomic
hierarchy from the phyla to the families in the
primate order
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Phyla in the Animal KingdomChordates
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Sub-phyla in the Chordate Phylum
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Sub-phyla in the Chordate Phylum Vertebrates
Sub-phylum
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Classes in the Vertebrate Sub-phylum
Sub-phylum
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Classes in the Vertebrate Sub-phylum Mammals
Sub-phylum
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Close-up Classes in the Vertebrate Sub-phylum
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Orders in the Mammal Class
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Orders in the Mammal Class Primates
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Families in the Primate Order
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Families in the Primate Order Hominoids
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Some key steps in the evolution of primates
note that our last common ancestor with other
modern primates was 6 to 10 MILLION years ago
Loss of dinosaurs, Rise of mammals
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Critical Thinking

• Is your uncle a monkey???

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Critical Thinking

• Is your uncle a monkey???

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(No Transcript)
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Two key steps bi-pedalism and large brain
Diagram phylogeny of humans, same diagram on
slide 73
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Critical Thinking

• Why is bi-pedalism so important?

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Critical Thinking

• Why is bi-pedalism so important?

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Images human fossil and fossil footprints
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Critical Thinking

• Why is a large brain so important?

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Critical Thinking

• Why is a large brain so important?

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The fossil record shows changes in our species
over time

• The path of human evolution is not ladder-like
• We are currently a mono-specific family, but.
• Human phylogeny reveals many extinct lineages
• We are animals
• We are subject to natural selection
• There is a record!

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All but one lineage of hominids are extinct
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Out of Africa Human Migration
Diagram multi-regional vs. out of Africa
hypotheses for human migration patterns same
diagram on following 2 slides
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Critical Thinking
How would you test these alternate hypotheses???
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Critical Thinking
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Evolution is a Constant

• Constant supply of genetic variation constant
  application of selection pressures
• All species are in some degree of flux
• New species are constantly diverging
• .and going extinct
• At any given time, we are just looking at a cross
  section of the process
• A slice through the crown of a multi-dimensional
  tree
• Evolution is NOT finished!

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.as the tree grows, so grows the tree of life
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Questions???
.as the tree grows, so grows the tree of life
Key Concepts

• Species concepts
• Development of reproductive isolation
• Patterns of speciation
• Macroevolution
• Human evolution
• Evolution continues..