Download BIO152 Natural Selection 1 Lecture outline

BIO152 Natural Selection 1
September 20
Lecture 4
Lecture outline
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Review-4 attributes of natural selection
Example-beak size Freeman 23.3
Artificial selection Freeman 1.2
Alternative hypothesis-inheritance of
acquired traits (Lamarck) Box 23.2
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Natural selection: 4 attributes
1. Only some offspring live long enough to
reproduce; some individuals survive and
produce more offspring
2. Individuals in a population vary in traits
3. Some variation is passed on to offspring:
heritable variation
4. Survival is not random -some heritable
traits offer an advantage to survive &
reproduce.
Table 1 Population growth in
Ideal Conditions
Initial population
Final population
2 elephants
750 years 1.9 x106
2 house flies
5 months 1.9 x1020
1 E. coli
48 hours
Cover earth to depth of 2m
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Table 2 Odds of survival in natural
conditions
Initial population
Final population
100 elephants
750 years later: 130
1000 house flies
5 months: 890
1x106 E. coli
48 hrs: 1.5x106
What factors affect survival?
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Natural Selection in action
Chapter 23 pp 506-508
Also The Beak of the Finch, John Weiner
Peter & Rosemary Grant Galapagos Islands:
Daphne Major
Studied the survival of the medium ground finches
during a severe drought in 1977
Where in the world…
• Series of slides showing maps to orient
you to where the Galapagos Islands are
and the ocean currents affecting rain fall
and nutrients
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Currents are like rivers in the ocean. This map shows the complexity of
currents surrounding the Galapagos. This situation has profound influences
on the Galapagos climate and hence its animals, especially due to the El
Niño effect.
During El Niño, the cold Humboldt Current from the south slackens off and the
islands are bathed in the warm waters of the Panama Current (arrow
labeled "Niño Flow"). Water and air temperatures rise and rainfall increases
dramatically. Land animals thrive.
On the other hand, nutrients the Humboldt normally brings to the islands, fall in
concentration so aquatic life, and seabirds that depend on it, suffers.
Currents were and still are important in transporting land and sea animals to
the Galapagos (see animal origins).
(http://www.junglephotos.com/galapagos/gmaps/scimaps/currents.shtml
Map modified from Michael H. Jackson, Galapagos: A Natural History Guide)
The Grants found that the offspring of the
birds that survived the 1977 drought
tended to be larger, with bigger beaks.
Hypothesis: the adaptation to a changed
environment led to a larger-beaked finch
population in the following generation.
[Figure 23.12]
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Did natural selection take place?
• Variable beak size—yes
• Heritable- (yes, birds with larger beaks
had offspring with larger beaks)
• Differential reproductive success-yes,
huge die back, only birds with larger beaks
survived
Unusually rainy weather in 1984-85 ►
More small, soft seeds & fewer of the large, tough
ones.
The birds best adapted to eat those seeds
because of their smaller beaks were the ones
that survived and produced the most offspring.
Evolution had cycled back the other direction.
It is possible to see evolution happen!
[Figure 23.13]
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Artificial selection
• [examples- on several slides]
Wild mustard
Corn
Dogs
Tulips
Natural selection
How does natural selection differ from
artificial selection?
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Artificial versus Natural selection
• Artificial selection selects for a trait WE deem
desirable, not necessarily ones to increase the
ability of the organism to survive and reproduce.
Artificial selection exaggerates the change in allele
frequency in a population for a specific trait &
any other linked traits. (Consider the affect of
artificial insemination on allele frequency)
(Think about this point after we discuss the Hardy
Weinberg principle later in the course)
Alternative hypothesis to natural
selection
Jean-Batiste do Lamarck early 1800s
Species are not static, but have changed
over time
Species not independently created entities
but are related by common ancestry
Earth is incredibly old
[He recognized the PATTERN part of
evolution]
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Lamarck’s Process
Inheritance of acquired traits
1. Simple forms of life continually created
by spontaneous generation.
2. Simple forms evolved into progressively
‘higher’ (larger & more complex) forms
3. Individuals change as they develop to
meet the challenges from their
environment.
• Lamarck did not support the idea of
extinction: for him, species that
disappeared did so because they evolved
into different species.
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Lamarck’s First Law: use or disuse
Organisms are not passively altered by their
environment:
• Instead, a change in the environment causes
changes in the needs of organisms living in that
environment, which in turn causes changes in
their behavior.
• Altered behavior leads to greater or lesser use
of a given structure or organ; use would cause
the structure to increase in size over several
generations, whereas disuse would cause it to
shrink or even disappear.
Lamarck’s Second Law:
Acquired traits are heritable
• Use/disuse changes were heritable.
• The result of these laws →
continuous, gradual change of all
organisms, as they became adapted to
their environments
The physiological needs of organisms,
created by their interactions with the
environment, drive Lamarckian evolution.
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While the mechanism of Lamarckian
evolution is quite different from that
proposed by Darwin, the predicted result is
the same:
adaptive change in lineages,
ultimately driven by environmental change,
over long periods of time
Lamarckian inheritance, (inheritance
affected by use or disuse), is in conflict
with the findings of genetics and has now
been largely abandoned -- but until the
rediscovery of Mendel's laws at the
beginning of the twentieth century, no one
understood the mechanisms of heredity,
and Lamarckian inheritance was a
perfectly reasonable hypothesis
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