Evolution, Speciation and Extinction

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Evolution, Speciation and Extinction

• Basic evolutionary theory
• Isolation and speciation
• Founder effects, bottlenecks, vicariance
• Adaptive radiation and evolutionary convergence
• Extinction

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Basic Evolutionary Theory

• Evolution genetically controlled changes in
  anatomy, physiology, and behavior in a species
  over time
• Natural Selection advantageous (reproduction)
  traits are selected for
• Speciation development of 2 (or more)
  genetically distinct species from single
  ancestor. The different species that arise are
  called a clade.

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• Genes are specific sequences found within
• molecules of DNA (chromosomes), which
• are combinations of sugars and phosphates
• bound together to form a double helix.
• The rungs of a chromosome consist of
• pairs the following nitrogenous compounds
• adenine (A)
• thymine (T)
• cytosine (C)
• guanine (G)

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DNA Double Helix
Nucleosome
Supercoil
Chromosome
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This stylistic diagram shows the locus of a gene
in relation to the double helix structure of DNA
and to a chromosome pair (right). Introns are
regions often found in eukaryote genes that are
removed in the splicing process (after the DNA is
transcribed into RNA) Only the exons encode the
protein.
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Gene expression transcription and translation
Genes are expressed by being transcribed into
messenger RNA, and this transcript may then be
translated into protein.
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Diagram showing the translation of mRNA and the
synthesis of proteins by a ribosome
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Genetic Diversity

• Polymorphism differences in a gene at a
  particular locus generate anatomical,
  physiological or behavioral differences in a
  population.
• Alleles - Different gene forms for a given locus
• Heterozygosity locus with many alleles creates
  variability in population

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Variability

• Phenotypic variability differences in
  physiology, anatomy, behavior between species or
  between individuals of the same species.
• Often stems from
• Genotypic variability differences between the
  genomes of species or individuals

An example of phenotypic variability that stems
from genotypic variability is Yarrow in Sierra
Nevada
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A geographic gradient in a genetically controlled
trait, such as the height of the yarrow plants,
is called a cline.
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Basic Genetic Concepts

• Genes are copied (dont change) during
  reproduction
• If the loci of the male and female dont match,
  no offspring
• Offspring are genetically similar to parents
• Genetic material come from both parents, so
  offspring are not clones
• Acquired traits are not passed on

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How do new traits arise?

• Genes subject to random mutation, sometimes
  creating new alleles
• Chromosomes can break and recombine imperfectly
  during transcription.
• Traits may be lethal, benign, or beneficial
• Genetic drift mutations over time in isolated
  population can lead to the development of a new
  species.

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Evolutionary Theory

• All species are naturally variable
• Genetic traits are inherited by offspring
• Natural selection traits that provide an
  advantage in reproduction are selected for,
  whereas disadvantageous traits are selected
  against. Advantageous traits are more likely to
  be passed on.

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How Does Speciation Occur?

• Reproductive isolation
• Instantaneous speciation Polyploidy
• Allopatric speciation Geographic separation
• Sympatric speciation occur without spatial
  barriers, but rather through reproductive
  isolation due to differences in timing and the
  complexities of mate choice, etc.
• Parapatric speciation different habitats in
  same geographic area disruptive selection

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Allopatric Speciation

• Isthmus of Panama 3mya
• Snapping shrimp diverged into separate species

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Sympatric Speciation

• Reproductive isolation
• Life cycle timing flowering etc.
• Mate choice
• Habitat selection creates isolation
• Organisms may in fact be isolated

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Peripatric Speciation

• different habitat in same geographic area

Anthoxanthum odoratum
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Geographic Effects on Evolution

• Founder principle an isolated population is
  less diverse than the ancestral population, and
  is cut off from alleles that may develop in the
  ancestral population
• Bottleneck decreased genetic diversity that
  results from a decreased population size,
  possibly caused by rapid environmental change.
• Peripatric speciation - accelerated genetic
  diversity in peripheral populations resulting
  from founder effect.
• Vicariance events the appearance of large
  geographic barriers that divide species ranges
  into isolated distributions.

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Founder Principle and Bottlenecks

• Rates of evolutionary change high in small,
  isolated, peripheral populations
• Quantum evolution GG Simpson
• Small pops already different from main gene pool
• Rapid speciation as few alleles mutate
• Quickly spread new alleles in small populations

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The divergence of lodgepole pine and jack pine
may have occurred allopatrically when
Pleistocene glaciations split the ancestral
distribution into western and eastern populations.
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Lodgepole pine
Jack pine
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Adaptive Radiation

• Development of many species from one to fill all
  available niches
• Many species of Hawaiian Honeycreepers developed
  from they arrival of one founding species

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Convergent Evolution the development of similar
morphological or physiological traits in
unrelated species living in geographically separat
ed regions.
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Succulents and Convergent Evolution
Euphorbia sp from Madagascar
Senita Cactus from Mexico
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Parallel evolution geographically isolated
populations devived from the same ancestor evolve
into morphologically and physiologically similar
descendant species. Coevolution - Unrelated
species evolve traits that are tied to their
interactions. Mutualistic associations can
develop when species are in close proximity.
Bumblebees and the flowers they pollinate have
coevolved so that both have become dependent on
each other for survival.
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Extinction

• Loss of all individuals of a species, genus,
  family or order
• Local extinction disappears in one region, but
  persists elsewhere
• Global extinction loss of a species or order
  over its entire range. Final.
• Phyletic extinction evolved into new species

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The widespread local extinction of the North
American bison original range, 1870, 1880,
1888 Captive breeding has led to a
resurgence over the last hundred years
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The horseshoe crab has existed in similar forms
for over 400 million years. Fossils recognisably
related to modern Ginkgo date back to the
Permian, some 270 million years ago.
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Long term Patterns of Extinction

• Background extinction rates plant families ¼
  million years, or one every 4 million years
• Catastrophic extinctions late Permian, late
  Devonian, late Cretaceous - 50-75 of animal,
  bivalve, dinosaur families

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Catastrophic extinction
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Why does background extinction occur?

• Cannot evolve quickly enough to keep pace with
  competitors (Red Queen phenomenon)
• Overspecialization
• Environmental change
• Bottleneck (loss of genetic diversity)

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Red Queen Phenomenon An evolutionary arms race
is an evolutionary struggle between competing
sets of co-evolving genes that develop
adaptations and counter-adaptations against each
other, resembling an arms race. For an
evolutionary system, continuing development is
needed just in order to maintain its fitness
relative to the systems it is co-evolving with.
"Now, here, you see, it takes all the running you
can do, to keep in the same place. If you want to
get somewhere else, you must run at least twice
as fast as that!"
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What Goes Extinct?

• Predators/large animals
• Complex organisms
• Small, isolated populations
• Slow reproductive rate
• Small range size
• Short dispersal range
• The extinction of one species can have a profound
  impact on its ecosystem. The loss of an important
  prey species can cause further extinctions
  because of the loss of food. Such events are
  called trophic cascades.

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The duration of a species may be influenced by
both population size and the birth/death
ratio, according to these results from a
mathematical model.
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The relationship between mass extinction and
speciation When a catastrophic
extinction occurs, many potential niches are
unfilled. Surviving species experience rapid
adaptive radiation as they speciate to occupy
these vacant niches.
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Rapid Evolution Guppy test subjects bump against
the confines of a holding tank where they'll swim
free in pools that dot isolated streams in
Trinidad.
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Once the guppies are released in Trinidad,
biologist David Reznick controls their exposure
to predators, then tracks changes in populations.
Body size, age at maturity, and number of young
have evolved in his experiments. "Darwin thought
evolution by natural selection was too slow to
observe," Reznick says. "But we're watching
evolution occur over just a few years."
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In the lab, paleontologist Neil Shubin studies
how body plans evolve. In larval skates (seen
here), he tinkered with a gene that, in humans,
influences hand shape. The result was a
predictable change in fin shape (at bottom).