section ii evolution and behavioral ecology 鄭先祐生態主張者 ayo [email protected]

Section IIEvolution and Behavioral Ecology

鄭先祐生態主張者 Ayo

[email protected]

2003 Chap. 2 Genetics and Ecology生態學 2

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 )


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.

Road Map


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


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.


Characterized by different inhabitants

• Australia: Ex. No native placental mammals except bats, variety of marsupials, egg-laying montremes, duck-billed platypus, and the echidna.

• Best explanation of differences: Evolution.


2.2 Genetic Mutation

• Increase in number of species is primarily due to mutation.

• Two types of mutation

– Gene or point mutation

– Chromosome mutation


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


Direction of transcription

DNA AGA TGA CGG TTT GCA

RNA UCU ACU GCC AAA CGU

Protein Ser AlaThr Lys Arg

Transition A-G

DNA GGA TGA CGG TTT GCA

RNA CCU GCC AAAACU CGU

Protein Pro Thr Ala Lys Arg

Frameshift: Insert T

DNA

RNA

Protein

AGT

UCA

ATG ACG GTT TGC A..

UAC UGC CAA ACG

Ser Tyr Cys Glu Thr ?

Fig. 2.1 Types of point mutation.


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


• 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.


Original

A B C D E F G HBreakage

G HA B C D E F A B C D E F H

Altered

A B C D E F G H

From another chromosome

A B C D E F G G H

A B G F E D C H

G

FE

D

C

H

Deletion

Duplication

Inversion

Translocation

A B C D E T U VA B C D E F G HA B C D E F G H

O P Q R S T U V O P Q R S T U V O P Q R S F G H

A B

G

Eliminated

Fig. 2.2 Chromosome breakage and reunion.


Fig. 7.15


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.


Fig. 2.3 Researcher examines an agarose gel on which samples are separated according to migration rates during the application of an electric current.


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.


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.


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.


Mutation • Accelerated through human-made radiation, UV lig

ht, 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.


2.4 Genetic Diversity and Population Size

• Function of population size

• Four factors:

– inbreeding,

– genetic drift,

– Neighborhoods,

– Effective population size


Inbreeding Depression

• 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).


Non-productivematings

60

50

40

30

10

20

0

Perc

ent

1 2 3 4 5 6

Mortality from birth to four weeks

Years

Fig. 2.4 inbreeding in rats.


0 5 10 15 20

A

B

C

0.2

0.4

0.6

0.8

1.0

Generations

Fract

ion o

f in

itia

l g

eneti

c vari

ati

on

Fig. 2.5 The decrease in genetic variation is faster the greater the inbreeding.

•A: exclusive self-fertilization

•B: sibling mating

•C: double-first-cousin mating


Saddle back tamarinUngulates

Primates

Small Animals

% Juvenile

mort

alit

y-

outb

red

70

60

50

40

30

20

10

0

Chimpanzee

Macaque

Lemur

Eld’s deer

Oryx

MouseMandrill

Indian elephant

Giraffe

10080604020

% Juvenile mortality-inbred

Spider monkeyRat

Fig. 2.6 The effects of inbreeding on juvenile mortality in captive populations of mammals.


Fract

ion o

f in

itia

l g

eneti

c vari

ati

on

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

N=20

N=100

N=300

N=1000

0 100 200 300 400 500

GenerationsFig. 2.7 finite population size


10

50

100

150

200 Eggs hatched

0

25

50

75

100

Prairie chicken cocks

Num

ber

of

pra

irie

chic

ken c

ock

s

1973 1980 1990

Year

Egg

s hatc

hed (

%)

Fig.2.9 decrease in hatching of prairie chicken eggs.


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.


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.


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.


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.


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)


Number of immigrants pergeneration

5

21

0.5

0.1

None

10 20 30 40 50 60 70 80 90 100

Generation

Perc

en

tage o

f in

itia

l g

eneti

c vari

ati

on r

em

ain

ing

50

60

70

80

90

100

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 generation can prevent the loss of heterozygosity through genetic drift.


Perc

en

tage o

f popula

tions

pers

isti

ng

0

20

40

60

80

100

10 20 30 40 50

Time (years)

N = 101 or more

N = 51-100

N = 31-50

N = 15 or less

N =16-30

Fig. 2.12


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.


Harem Effects

• Even within a neighborhood, some individuals may not reproduce.

• In a harem structure, only a few dominant males breed.


Effective Population Size

• NE = (4 Nm Nf) / (Nm + Nf).

• Where:

– NE = Effective Population Size;

– Nm = Number of Breeding Males;

– Nf = Number of Breeding Females.


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.


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.

Applied Ecology


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Ayo 台南站： http://mail.nutn.edu.tw/~hycheng/

section ii evolution and behavioral ecology 鄭先祐 生態主張者 ayo [email protected]

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section ii evolution and behavioral ecology 鄭先祐生態主張者 ayo [email protected]