lecture #3 – origin of species
DESCRIPTION
Lecture #3 – Origin of Species. Cartoon – gentleman and ape. Key Concepts:. Species concepts Development of reproductive isolation Patterns of speciation Macroevolution Human evolution Evolution continues…. specie. My pet peeve is…. “Species” is both singular and plural. - PowerPoint PPT PresentationTRANSCRIPT
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Lecture #3 – Origin of Species
Cartoon – gentleman and ape
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Key Concepts:
• Species concepts• Development of reproductive isolation• Patterns of speciation• Macroevolution• Human evolution• Evolution continues…..
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specie
“Species” is both singular and plural
My pet peeve is….
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Diagram – variation in beaks between species
Major Species Concepts
• Biological• Morphological• Phylogenetic
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Image – Sarracenia flava Image – Sarracenia rubra
Biological species – the basic standard for separating species (Ernst Mayr, 1942)
• Species are defined by natural reproductive isolationIndividuals that can produce successful
offspring are considered the same species
≠
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Critical Thinking
• Biological species are defined by natural reproductive isolationIndividuals 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 isolationIndividuals that can produce successful
offspring are considered the same species• Definition doesn't always work
Speciation often occurs as the gradual divergence of multiple populations
Fuzzy boundaries during divergence• Also, can’t be used to classify extinct
species
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Image – Hymenocallis floridanaImage – Hymenocallis coronaria
Morphological species – the first way to separate species (Linnaeus, ~1750 & others)
• Species are defined by differences in formIndividuals with the same morphology and/or
anatomy are considered the same species
≠
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Critical Thinking
• Morphological species are defined by differences in formIndividuals 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 formIndividuals with the same morphology and/or
anatomy are considered the same species• Definition doesn't always work
Some species have a lot of natural phenotypic variation
• But, the only way to classify extinct species and species that lack sexual reproductionAlso important in describing new species
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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 treeMonophyletic = lineage is derived from a
common ancestor• Definition doesn't always work
Don’t have good phylogenies for all species or groups
Also, imperfect agreement on interpretations
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Development And Maintenance Of Reproductive Isolation: the essence
of speciation
• What constitutes a barrier to reproduction?• How do reproductive barriers develop?
It is generally accepted that natural reproductive isolation defines and
preserves separate species in sexually reproducing organisms
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Image – blue-footed boobies mating behavior
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 fertilizationHabitat isolationBehavioral isolationTemporal isolationStructural isolationChemical isolation
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Critical Thinking
• Natural, evolved incompatibilities prevent successful fertilization
• Think of some examples of:Habitat isolationBehavioral isolationTemporal isolationStructural isolationChemical isolation
Euphorbia in very xeric habitat
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Critical Thinking• Habitat isolation – different ecological
niches• Behavioral isolation – changes in mating
behaviors….• Temporal isolation – the timing of
reproductive events• Structural isolation – mutations that change
morphology of reproductive structures• Chemical isolation – gametes must be
compatible, pollen must “match”
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Post-zygotic Barriers• Post-zygotic barriers prevent successful
development of offspringHybrids don’t develop properlyHybrids don’t reach sexual maturityHybrids don’t produce viable gametesHybrid 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
a. its ability to reproduce.b.how long it lives.c. the number of mates it attracts.d. the number of its offspring that survive
to reproduce.e. its physical strength.
The Darwinian fitness of an individual is measured by
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Critical Thinking
a. its ability to reproduce.b.how long it lives.c. the number of mates it attracts.d.the number of its offspring that survive
to reproduce.e. its physical strength.
The Darwinian fitness of an individual is measured by
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Diagram – different species of fish in separated ponds
Patterns of SpeciationBarriers result from separations that persist long
enough that eventually new species have developed
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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 barrierSympatric 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 • Such as rivers, canyons, mountains, oceans,
glaciers…..• How could such barriers form???
Diagram showing development of a canyon
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Critical Thinking• Allopatric speciation occurs when populations are
separated by a geographical barrier • Such as rivers, canyons, mountains, oceans,
glaciers…..• How could such barriers form???• Geological processes
Mountain buildingRiver erosionGlaciationTectonic eventsCave formation
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Critical Thinking• Also….• Climate changes that cause large lakes to
dry up or form smaller, isolated lakes• Colonization events that separate a group
from the rest of the population (founder effect)
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Allopatric Speciation• Once populations are physically isolated,
speciation may occur due to all the evolutionary processes we talked about earlier SelectionDriftSelective matingMutation
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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???Speciation is likely to occur more rapidlyMore genetic drift, less gene flow
• 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???Speciation is likely to occur more rapidlyMore genetic drift, less gene flow
• What if the isolated population is from edge of the range of the original population???It may be even more likely to divergeProbably already adapting to frontier or edge
conditionsAlso, probably more likely to migrate
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Allopatric Speciation due to geographic separation
Images – different species of chipmunk on either side of the Grand CanyonP
lant
s???
? Birds????
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Diagram – sympatric allopatric either sympatric again or not, as a population separates around a mountain range and then re-unites
Speciation may, or may not, occur…
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Diagram – sympatric speciation in a forest environment
Sympatric Speciation• Occurs when a population
becomes reproductively isolated without geographic barriersMutations 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 or multiple events (mostly plants)
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Diagram – meiosis errors
Sympatric Speciation• Occurs when a population
becomes reproductively isolated without geographic barriersMutations 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 or multiple events (mostly plants)
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Polyploidy – one mechanism for sympatric speciation
Diagram – errors in meiosis can lead to polyploids
Some plants can self-pollinate, or vegetative reproduction can produce multiple fertile individuals
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Sympatric Speciation• Occurs when a population
becomes reproductively isolated without geographic barriersMutations 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 or multiple events (mostly plants)
Image showing hybrid asters
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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 produce 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 placeVolcanic island chains often contain many endemic
speciesNo biota until they were colonized by a few individuals
(founder effect)• These small populations then evolved into new
speciesAllopatric 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 islandsSympatric speciationNo geographic barriersAdaptive radiation into new habitats
Diagram showing adaptive radiation
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Diagrams – adaptive radiation in birds
Adaptive Radiation
Galapagos finches and Hawaiian honeycreepers
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Diagram – diversification of mammals after extinction of the dinosaurs
Diagram – mass extinctions over the past 2.5 billion years
Adaptive Radiation is a common theme – both between and within lineages
MammalsMass Extinction Events
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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???Highly unlikelyThere will just be a new set of species
• 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???
Highly unlikelyThere will just be a new set of species
• Can we destroy the planet???Highly unlikelyThe earth has survived for at least 4 billion
years!Species come and go….
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Speciation is a Constant
• When migration, isolation or other selection pressures force divergence, reproductive isolation can eventually lead to speciationSpeciation 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 organisms
Also 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 genesControl over the timing and length of
developmental events, or the spatial organization of body parts
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Diagram – phylogeny of the modern horse
Critical Thinking
Was the evolution of the modern
horse a series of directed events????
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Critical Thinking
• No, there are lots of lineages that are now extinct
• Evolution may look directed, but it’s not....
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 Hierarchy:this is how we classify diversity
Taxonomic Category Example (taxon)
Domain Eukarya = all eukaryotic organisms
Kingdom Plantae, also Metaphyta = all plants
Division (phylum) Magnoliophyta = all angiosperms
Class Liliopsida = all monocots
Order Asparagales = related families (Orchidaceae, Iridaceae, etc)
Family Orchidaceae = related genera (Platanthera, Spiranthes, etc)
Genus Platanthera = related species (P. ciliaris, P. integra, etc)
Specific name/epithet ciliaris = one species
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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
Image of human fossil
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Phyla in the Animal Kingdom:Chordates
This and next 6 slides show the phylogenetic placement of humans in the animal kingdom
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Sub-phyla in the Chordate Phylum: Vertebrates
Sub-phylum
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Classes in the Vertebrate Sub-phylum: Mammals
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Close-up: Classes in
the Vertebrate
Sub-phylum
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Orders in the Mammal Class:
Primates
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Families in the Primate
Order: Hominoids – a monotypic
family
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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
Diagram showing the different orders of primates
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Critical Thinking
• Is your uncle a monkey???
Cartoon showing gentleman and ape
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Critical Thinking
• Is your uncle a monkey???• Of course not!!!• Humans are NOT evolved from monkeys!
Diagram showing phylogenetic relationships between primates
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Monkeys, apes and humans share a common ancestor, but have followed different
evolutionary pathways for > 6 million years!
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Diagram – phylogeny of humans
Two key steps – bi-pedalism and large brain
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Critical Thinking
• Why is bi-pedalism so important?
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Critical Thinking
• Why is bi-pedalism so important?• Bipedalism functionally separates the limbs• Legs for energy efficient walking and
elevation of the eyes• Arms for hunting, gathering, tool use, caring
for offspring, artistic endeavors, etc….Current evidence is that this divergence began
6-10myaComplete conversion in hominids by about
2mya
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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?• Large brain allows for complex thought,
abstract reasoning, spirituality, creativity, language, complex toolsMost of the traits that we consider uniquely
human…Larger brain began emerging about 2mya,
stable for about 200,000 years
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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 lineagesWe are animalsWe are subject to natural selectionThere is a record!
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All but one lineage of hominids are extinct
Diagram – phylogeny of humans
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Diagram – multi-regional vs. “out of Africa” hypotheses for human migration patterns; same diagram on following 2 slides
Out of Africa – Human Migration
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Critical Thinking
How would you test these alternate hypotheses???
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Critical Thinking
DNA evidence supports this
pathway
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Evolution is a Constant• Constant supply of genetic variation +
constant application of selection pressuresAll 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 processA 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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….as the tree grows, so grows the tree of life…
• Species concepts• Development of
reproductive isolation• Patterns of speciation• Macroevolution• Human evolution• Evolution continues…..
Key Concepts:
Questions???
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Hands On
• We’ll be starting with plants next time• Bring in samples of plants to examine
microscopically and macroscopically• Anything that interests you – from nature,
your kitchen, garden…..• Parts or whole plants• Save reproductive parts for later in the
week