Transcript Section II Evolution and Behavioral Ecology

Section II
Evolution and Behavioral Ecology
鄭先祐
生態主張者 Ayo
[email protected]
Section Two
Evolution and Behavioral Ecology
• Chap.2 Genetics and Ecology (遺傳與生態)
• Chap.3 Extinction (滅絕)
• Chap.4 Group selection and individual selection
• Chap.5 Life History Strategies (生活史的策略)
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Road Map
Chap. 2 Genetics and Ecology
1. Species occurrence due to evolutionary past.
2. Mutations and chromosomal rearrangements
result in a wide variety of species on earth.
3. Genetic variability can be measured by
allozymes or DNA sequencing.
4. Mechanisms for reductions in genetic
variability in populations.
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2.1 Evolutionary History
• Importance of evolutionary ecology to the
discipline.
• Example: Control of penguins in the
Southern Hemisphere vs. their absence in
Northern Hemisphere.(企鵝只發現於南半球)
– Penguins evolved in the Southern Hemisphere.
– Unable to migrate to Northern Hemisphere
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Evolutionary history
• South America, Africa, and Australia
– Similar climates (Tropical to temperate)
– Characterized by different inhabitants.
• South America: Ex. Sloths, anteaters,
armadillos, and monkeys with prehensile
tails.
• Africa: Ex. Antelopes, zebras, giraffes, lions,
baboons, okapi, and aardvark.
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Characterized by
different inhabitants
• Australia: Ex. No native placental
mammals except bats, variety of
marsupials, egg-laying montremes, duckbilled platypus, and the echidna.
• Best explanation of differences: Evolution.
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2.2 Genetic Mutation
• Increase in number of species is primarily
due to mutation.
• Two types of mutation
– Gene or point mutation
– Chromosome mutation
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Point mutation
• Results from a misprint in DNA copying
– Example (Figure 2.1)
• Most changes are caused by frameshift
mutations
– An addition or deletion in the amino-acid
sequence usually leads to drastic and often
fatal mutations
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Direction of transcription
DNA AGA
TGA
RNA UCU
ACU GCC
AAA CGU
Thr
Lys
Protein Ser
CGG
Ala
TTT
GCA
Arg
Frameshift: Insert T
Transition A-G
DNA GGA TGA
CGG
TTT
GCA
DNA AGT
ATG
ACG
RNA CCU
GCC AAA
CGU
RNA UCA
UAC
UGC CAA ACG
Protein Ser
Tyr
Protein Pro
ACU
Thr
Ala
Lys
Arg
Cys
GTT TGC
Glu
Thr
A..
?
Fig. 2.1 Types of point mutation.
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Chromosome mutation
• Four types: deletion, duplications,
inversions, and translocation (Figure 2.2)
• Deletion
– Simple loss of part of a chromosome
– Most common source of new genes
– Often lethal
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• Duplication
– Arises from chromosomes not being perfectly
aligned during crossing over.
– Results in one chromosome being deficient and
the other one with duplication of genes.
– May have advantages due to increased enzyme
production.
• Inversion
– Occurs when a chromosome breaks in two
places. When the segment between the two
breaks refuses, it does so in reverse order.
– Occurs during prophase.
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Original
Breakage
A B C D E FG H
Altered
A BC D E F G H
Deletion
A B C D E F H
Eliminated
A B C D E F
Duplication
From another
chromosome
F
Inversion
A B C D E F G G H
G
E
A B G F E DC H
D
G
A B
GH
C
H
A B C D E FG H
A B C D E
FGH
A B C D E T U V
O P Q R S T U V
O P Q R S
TUV
O P Q R S F G H
Translocation
Fig. 2.2 Chromosome breakage and reunion.
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Fig. 7.15
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Fig. 7.15
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Fig. 7.15
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2.3 Measuring Genetic Variability
• Genetic diversity is essential to the breeding
success of most populations.
• Two individuals with the same form of enzyme are
genetically identical at that locus.
• Variations in gene loci are found through
searching for variations in the enzymes
(allozymes).
• Gel electrophoresis: Technique for determining
differences in allozymes.
• Example of Gel electrophoresis: Figure 2.3.
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Fig. 2.3 Researcher examines an agarose gel on
which samples are separated according to migration
rates during the application of an electric current.
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Gene Sequencing
• Another method for assessing variations is
the sequence of DNA.
• Made possible through the polymerase
chain reaction (PCR) technique.
• Made possible through the polymerase
(cont.).
– Makes millions of copies of a particular region
of DNA, thereby amplifying even minute
amounts of DNA.
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DNA amplified
• DNA可以經由 polymerase chain reaction
(PCR) 被 amplified (increased)。
• 將片斷的DNA與nucleotides 和DNA
polymerase混合。DNA polymerase可以促
使DNA複製。
• DNA將會持續複製到nucleotides耗盡。速
度相當快。於幾個小時內，就可以有1,000
億個copies(DNA)。 (Fig.8.3)
教科書：Wallace, R. A. (1997) Biology: the world of life.
Addison Wesley Longman, Inc.
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Fig. 8.3 DNA片斷 複製增加的方法。經過25個周期，就可
以有1,000,000個copies。
教科書：Wallace, R. A. (1997) Biology: the world of life.
Addison Wesley Longman, Inc.
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Mutation
• Accelerated through human-made radiation, UV
light, or other mutagens.
• Rate of occurrence: one per gene locus in every
100,000 sex cells.
Only one out of 1,000
mutations may be beneficial.
• Estimated that only 500 mutations would be
expected to transform one species into another.
• Rate of mutation is not the chief factor limiting the
supply of variability.
• Variability is mainly limited by gene recombination
and the structural patterns of chromosomes.
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2.4 Genetic Diversity and
Population Size
• Function of population size
• Four factors:
– inbreeding,
– genetic drift,
– Neighborhoods,
– Effective population size
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• Mating among close relatives.
• Reduced survivorship (Figure 2.4).
• Various types of inbreeding (Figure 2.5)
• inbreeding on juvenile mortality (fig. 2.6)
• inbreeding on small populations (Figure 2.7).
• Greater Prairie Chicken (Figures 2.8 and 2.9).
Inbreeding Depression
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Percent
60
50
Non-productive
matings
40
Mortality from
birth to four
weeks
30
20
10
0
1
2
3
4
5
6
Years
Fig. 2.4 inbreeding in rats.
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Fraction of initial genetic variation
1.0
•A: exclusive self-fertilization
0.8
C
•B: sibling mating
•C: double-first-cousin mating
0.6
B
0.4
A
0.2
0
5
10
15
20
Generations
Fig. 2.5 The decrease
in
genetic
variation
is
faster
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% Juvenile mortality- outbred
70
Primates
60
Small Animals
50
40
Saddle back tamarin
Ungulates
Macaque
Chimpanzee
Lemur
30
Giraffe
20
10
0
Rat
20
40
Eld’s deer
Indian elephant
Spider monkey
Oryx
Mandrill
Mouse
100
80
60
% Juvenile mortality-inbred
Fig. 2.6 The effects of inbreeding on juvenile
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1.0
N=1000
Fraction of initial genetic variation
0.9
0.8
N=300
0.7
0.6
N=100
0.5
N=20
0.4
0.3
0.2
0.1
0
100
200
300
400
Fig. 2.7 finite population
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Chap. 2 Genetics andGenerations
Ecology
500
27
hatched
100
75
Eggs hatched (%)
150
Prairie chicken cocks
100
50
50
25
10
Number of prairie chicken cocks
Eggs
200
Fig.2.9 decrease in hatching of
prairie chicken eggs.
0
1973
1980
Year
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Greater prairie chicken
• 1933, population size is 25,000
• 1962, population size is 2,000
• 1990, population size is 76
• Less than 50 in 1994
• Prairie chicken habitat was restored in 1970s
and hunting had been banned since the 1940s.
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Inbreeding and extinction
• Glanville fritillary butterfly (Figure
2.10)
• Exists in numerous small, isolated
local populations in meadows
where the caterpillars feed on one
or two host plants.
• Seven of the 42 populations studied
became extinct between 1995 and
1996; all seven had a lower
population size and genetic
variation than the survivors.
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Genetic Drift
• Probability of the failure to mate
– Loss of possible rare gene
– Loss of genetic information for subsequent generations
resulting in a loss of genetic diversity.
– Small populations more susceptible to drift.
– The rate of loss of original diversity over time is
approximately equal to 1/2N per generation.
– Example: N = 500 , then 1/2N = 0.001 or 0.1% genetic
diversity lost per generation.
– N = 50, then 1/2N = 0.01 or 1% genetic diversity lost per
generation.
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Probability of the failure to
mate
• Over 20 generations, the population of
500 will still retain 98% of the original
variation, but the population of 50 will
only retain 81.79%.
• 50/500 Rule: Need 50 individuals to
prevent excess inbreeding and 500 is the
critical size to prevent genetic drift.
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Genetic drift
• Effects of immigration on genetic drift
(Figures 2.11 and 2.12).
• Even the relatively low rate of one
immigrant every generation would be
sufficient to counter genetic drift in a
population of 120 individuals.(Fig. 2.11)
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Number of
immigrants per
generation
Percentage of initial
genetic variation remaining
100
5
2
1
90
80
0.5
70
0.1
60
None
50
10
20
30
40
50
60
70
80
90
100
Generation
Fig. 2.11 The effect of immigration on genetic variation in 25 simulated
population of 120 individuals each. Even the low rate of one immigrant per
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Percentage of populations persisting
100
N = 101 or more
80
N = 51-100
N =16-30
60
N = 31-50
40
N = 15 or less
20
0
10
Fig. 2.12
20
30
40
50
Time (years)
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Neighborhoods and Effective
Population Size
• Effective population size is determined on
mating range.
• Individuals may only mate within their
neighborhood.
• Example: Deer mice. 70% of the males
and 85% of the females breed within
150m of their birthplaces.
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Harem Effects
• Even within a neighborhood, some
individuals may not reproduce.
• In a harem structure, only a few dominant
males breed.
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Effective Population Size
• NE = (4 Nm Nf) / (Nm + Nf).
• Where:
– NE = Effective Population Size;
– Nm = Number of Breeding Males;
– Nf = Number of Breeding Females.
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Effective Population Size
• A population of 500 with a 50:50 sex ratio
and all individuals breeding.
– NE = (4 x 250 x 250) / (250+250) = 500
• If 250 females bred with 10 males.
– NE = (4 x 10 x 250) / (10 +250) = 38.5
– Only 7 percent of the actual population size.
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Applied Ecology
Can Cloning help save
endangered species?
•
Dolly, the cloned sheep – Ian Williams
1997 (Photo 1).
1. Need knowledge of reproductive cycle.
2. Need for surrogate females.
3. Expense associated with cloning.
4. Can not address genetic diversity.
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 問題與討論！
[email protected]
Ayo 台南站： http://mail.nutn.edu.tw/~hycheng/
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