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Lecture 13 The source of novelty
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Lecture 13 The source of novelty
Natural Selection Adaptive Radiation Mutations
Hybridization Polyploidy
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Introduction Every species is adapted to a
combination of factors (Phy. Environment,
Range of variation, food supply, competiti
on, occasional losses due to disease,
predation) Puts demands on the Structure or
Physiology of the organism Some are obvious and
some are more complex
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Introduction Early 19th Century accepted
that each species had always
existed precisely as we now see it God was
thought to have created each one (including
adaptations, and that these remained unchanged
through time)
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It (biological design) indeed does destroy the
most powerful arguments of God.
Famous Reply of French Mathematician Pierre
Simon de Laplace (1749-1827) to Napoleon is
now truer than ever.
Laplace argued for Biological design by natural
selection rather than divine creation.
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Introduction Explanation for Fossils God had
destroyed the species during Catastrophes! e.g.
The Biblical Flood
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Darwins Journey Around the World-HMS Beagle
Two Observations Galapagos Islands/Mainland
South America Reconsidered the assumptions of the
day (Finches and Fossils)
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Darwins Journey Around the World-HMS Beagle
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Natural Selection Basic Philosophy of
Biological Science Published by Darwin in 1858.
Natural selection is the evolutionary process by
which favorable traits that are heritable become
more common in successive generations of a
population of reproducing organisms and
unfavorable traits that are heritable become less
common.
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Natural Selection Natural selection acts on the
phenotype, or the observable characteristics of
an organism, such that individuals with favorable
phenotypes are more likely to survive
and reproduce than those with less favorable
phenotypes.
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Natural Selection The favorable phenotypes
will have a natural advantage in the
competition for life They will survive at the
expense of their less fortunate Relatives, by
their survival and eventual mating the process of
NS will to the persistence of these favorable
characteristics
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Natural Selection So why should each species
not be able to evolve to one single answer to
the demands that the environment makes upon
it? All flowers of a particular plants species
would then have the same color? every sparrow
have the same beak size? Such a simple solution
is not possible, because the Env. is neither
stable nor uniform
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Natural Selection in Action
Darwin's Finches (Flock from SA 2-3 mya)
Darwin's finches are an excellent example of the
way in which species' gene pools have adapted in
order for long term survival via their offspring.
Once thought that evolution took place
too slowly for it to be detectable over the
timescale of scientific studies of living
organisms-but no! Adaptive Radiation evolve and
radiate into ways not formerly available to it
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Adaptive Radiation
In an adaptive radiation, a "founder" species
enters a new environment with many unoccupied
niches. This species expands (radiates) and
evolves adaptations to fit these niches better.
The process of becoming adapted to these
different niches may lead to, and in these cases
has led to, the formation of new species.
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Natural Selection in Action
Darwin's Finches
The finches hold a unique place in the history of
science. The birds, which live only on the
Galapagos, were studied closely by Charles Darwin
on his Beagle voyage in the 1830s. Observations
on the shapes of the birds' beaks were central in
helping Darwin formulate his theory of evolution.
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Natural Selection in Action
Darwin's Finches
Among the Darwin's finches, there is
general agreement as to the existence of 13
Galapagos species, although there may be one or
two more or one or two less, depending on how one
assesses several unusual populations.
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Darwin's 13 Finches
Narrow Bills -live on the ground and feed on
insects, snails etc Strong, heavy bills -live in
cactus thickets, feed on cactus seeds, flowers,
pollen Most live in bushes/trees -feed on seeds,
nuts, fruits
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Darwin's Finches Difficult to separate out! Even
for Ornithologists
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Natural Selection in Action
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Natural Selection in Action
Darwin's Finches
All the species of finches on the Galápagos
Islands appear morphologically very similar,
varying mostly in terms of beak size and
behavior they all look very much like a species
of finch from the mainland of South America.
This suggests that all the finches on the
Galápagos are descended from one original
colonist species that went through an adaptive
radiation.
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Natural Selection in Action
Darwin's Finches
The Darwin's Finches diagram illustrates the way
the finch has adapted to take advantage of
feeding in different ecological niche's.
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Natural Selection in Action
Darwin's Finches
Their beaks have evolved over time to be best
suited to their function. For example, the
finches who eat grubs have a thin extended beak
to poke into holes in the ground and extract the
grubs.
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Natural Selection in Action
Darwin's Finches
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Natural Selection in Action
Darwin's Finches
Finches who eat buds and fruit would be less
successful at doing this, while their claw like
beaks can grind down their food and thus give
them a selective advantage in circumstances where
buds are the only real food source for finches.
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Galápagos Islands
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Galápagos Islands
Because of the small, isolated environment of the
Galápagos, the finches have become the topic of
extensive study into natural selection.
The studies that have been conducted on the
finches show strong selection for larger beaks
during droughts (e.g. 1977).
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Galápagos Islands
The studies that have been conducted on the
finches show strong selection for larger beaks
during droughts (11 mm ideal for drought years).
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Galápagos Ground Finches with beaks of different
size.
(11 mm ideal for drought years).
Tribulus Fruits-some Having been opened by
Finches, who have removed the seeds
leaving holes
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Beak depth, which is correlated with body size
and the ability to crack larger seeds, varies
according to drought conditions, which produce
fewer, harder seeds in dry years and more and
softer seeds in wet years. The change is 5 in
extreme years. The graph shows a pattern of
stabilizing selection, in which beak depth
fluctuates around a mean of about 9.6mm.
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Galápagos Islands
These data show that climatic changes can have
profound effects on the morphology of a species
and potentially lead to the formation of new
species.
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Galápagos Islands
Short term climatic change
Rainfall
Finch population
Biomass of small seeds
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The difficulty in identifying the finches is
rooted in precisely what makes them so
interesting and important - the evolutionary
process.
If we believe that two species share a common
ancestor, then as one traces the species back in
time, they should become closer and closer in
form. At the branch point, the species should
become ambiguous.
That is precisely the point at which we find the
Darwin's finches.
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They are in the process of separating, but they
haven't completely done so at this point in
time. The definition of the term "species"
includes the presence of a fertility barrier
between individuals of different species.
In the case of Darwin's finches, those barriers
are not completely formed yet, and there is a
certain amount of documented hybridization
between species. This also contributes to the
ambiguity of the birds.
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Our current understanding of evolution is that
new species are born when the population of the
ancestor species is split.
Once the gene pool is separated, the two
populations may be subject to different natural
selection pressures, and hence, evolve in
separate ways.
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The splitting of a population followed by
subsequent evolution is known as allopatric
speciation.
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Our current understanding of evolution is that
new species are born when the population of the
ancestor species is split.
Once the gene pool is separated, the two
populations may be subject to different natural
selection pressures, and hence, evolve in
separate ways. The splitting of a population
followed by subsequent evolution is known as
allopatric speciation. At some point, the
populations may come back together again, that
is, they may become sympatric.
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A variety of possibilities arise when two
populations, born in allopatry become sympatric
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A variety of possibilities arise when two
populations, born in allopatry become sympatric
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A variety of possibilities arise when two
populations, born in allopatry become sympatric
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Darwin's finches have many other evolutionary
tales to tell. Darwin himself used the finches
in the The Voyage of the Beagle to quietly
announce the theory of evolution "Seeing this
gradation and diversity of structure in one
small, intimately related group of birds, one
might really fancy that from an original paucity
of birds in this archipelago, one species had
been taken and modified for different ends."
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Interesting side note
When Darwin visited the Galápagos, he observed
and collected some of the finch species,
believing that they represented a very diverse
set of birds that were not closely related.
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Interesting side note
When Darwin visited the Galápagos, he observed
and collected some of the finch species,
believing that they represented a very diverse
set of birds that were not closely related.
Their significance was not recognized until
later, when ornithologist John Gould pointed out
that the birds were all closely related finches
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Interesting side note
When Darwin visited the Galápagos, he observed
and collected some of the finch species,
believing that they represented a very diverse
set of birds that were not closely related.
Their significance was not recognized until
later, when ornithologist John Gould pointed out
that the birds were all closely related finches
But because Darwin originally collected some of
the specimens and because the finches showed so
much evidence for evolution and natural
selection, they have been dubbed "Darwin's
finches." This has led many people to conclude
(mistakenly) that Darwin's theory of evolution
was specifically inspired by the finches
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Controlling Forces Within the organism Mutations
Sudden alterations in the genetic make up of
individuals. Sometimes there is a slight error
from time to time the in gene duplication during
cell division (biological a very complex process
and mistakes occur!). Cell-Nucleus-Chromosomes-G
enes-Alleles (different versions of the Gene
-hair color (brown, red, black, blonde)
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Controlling Forces Within the organism Mutations
Changes in the genetic system can lead to
changes in the characteristics of an isolated
population in two ways. Mutations may appear and
prove advantageous Second, each ind. carries
several thousand genes, and each maybe present in
one of its several thousand alleles, no
two individuals carries the same genetic code or
genotype-unless they are identical twins.
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Controlling Forces Within the organism Mutations
Inevitably, isolated populations will come to
differ from others in its genetic content, some
alleles being rarer or absent. As mating
continues new combinations appear leading
to further differences later
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Controlling Forces Within the organism Genetic
Drift In small populations, where chance plays a
greater role in controlling whether a particular
allele becomes common or Rare or
disappears. Smaller populations contain less
genetic variability and are closely adapted to
the environment.
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Controlling Forces Within the organism Phenotype
The way in which a genotype of an organism is
expressed in its morphology, physiology, behavior
etc is known as the phenotype. Plasticity of an
organism-adapted to the demands of the
environment
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Hybridization (Hybrids of Two Independent
Pops-usually along a narrow zone of contact
where the two meet). The offspring of two
different species, or of two different
genera. Once separated (barriers), they speciate
in isolation, but once they are re-united they
can still interbreed-resulting in reduced
fertility or sterility.
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Hybridization (Hybrids of Two Independent
pops-usually along a narrow zone of contact
where the two meet) Mule, a cross of female
horse and a male donkey. Hinny, a cross between
a female donkey and a male horse.
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• Hybridization
• Natural interspecific hybridization in oaks
  (Quercus)
• California Black Oak (Q. kelloggii), a tall,
  deciduous tree
• Interior Live Oak (Q. wislizenii var.
  frutescens),
• a large, evergreen shrub
• C. Oracle Oak (Q. x morehus), a small, partly
  deciduous tree
• that retains numerous leaves during the winter
  months.

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Polyploidy the condition of having three, four,
or more sets of chromosomes instead of the two
present in diploids.
Is the doubling of the whole set of chromosomes
in the nucleus of a developing egg or seed, so
that each has a identical partner. This is an
important mechanism in speciation.
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Polyploidy
Common in groups in which self fertilize e.g.
weeds, wheat breads of the world, potatoe, sugar
cane, coffee, maize, cabbage!