Macro evolution-natural-selection-speciation

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Populations are the units of evolution

Figure 13.6

1. What is evolving? gene pool, microevolution

2. Five agents of evolution

3. Types of natural selection

Why do organisms change?

• Evolution happens when populations of organisms with inherited variations are exposed to environmental factors that favor the reproductive success of some individuals over others

Figure 1.6C


Populations are the units of evolution

• A population is a group of interbreeding individuals

• A species is a group of populations whose individuals can interbreed and produce fertile offspring

Figure 13.6


• gene pool = total collection of genes in a population at any one time

• Microevolution is a change in the relative frequencies of alleles in a gene pool

What is evolving?

Five agents of microevolution

1. Mutation changes alleles

2. Genetic drift = random changes in allele frequency

Bottleneck

Founder effect

LARGE POPULATION = 10,000 SMALL POPULATION = 10

allele frequency =1,000

10,000 = 10% allele frequency =1

10 = 10%

50% of population survives,including 450 allele carriers

50% of population survives,with no allele carrier amongthem

allele frequency =450

5,000 = 9% allele frequency =05 = 0%

little change in allele frequency(no alleles lost)

dramatic change in allele frequency(potential to lose one allele)

Genetic drift - effects of population size:


Founder effect

Figure 13.11B, C

Bottleneck effect

Population size is critical in preserving species.


3. Gene flow can change a gene pool due to the movement of genes into or out of a population

ex. Migration

4. Nonrandom mating within a population

5. Natural selection leads to differential reproductive success


• Male and female lions

Figure 13.20x


• Natural selection

- results in the accumulation of traits that adapt a population to its environment

- the only agent of evolution that results in adaptation.


What are sources of genetic variation?

• Mutation can create new alleles, new genes.

• Sex - Recombination of genes in sexual reproduction


• Natural selection tends to reduce variability in populations. Mechanisms which counteract:

– The diploid condition preserves variation by “hiding” recessive alleles (Bb)

– Balanced polymorphism (2+ phenotypes stable in population) may result from:

1. heterozygote advantage Aa > aa and AA

2. frequency-dependent selection

3. variation of environment for a population

Why doesn’t natural selection eliminate all genetic variation in populations?


• Many populations exhibit polymorphism and geographic variation

Figure 13.13


• Neutral; no apparent advantage or disadvantage

– Example: human fingerprints

Not all genetic variation may be subject to natural selection

Figure 13.16


• Low genetic variability may reduce their capacity to survive as humans continue to alter the environment

– cheetah populations

Endangered species often have reduced variation

Figure 13.17


• the contribution it makes to the gene pool of the next generation relative to the contribution made by other individuals

• Production of fertile offspring is the only score that counts in natural selection

What is an organism’s evolutionary fitness?


There are three general outcomes of natural selection

Figure 13.19

Fre

qu

en

cy

of

ind

ivid

ua

ls

Originalpopulation

Phenotypes (fur color)

Originalpopulation

Evolvedpopulation

Stabilizing selection Directional selection Diversifying selection

beak depth

1976

1978Averagebeak depth,1978

Averagebeak depth,

1976

Beak depth (mm)

Shift of average beakdepth during drought

5 6 7 8 9 10 11 12 13 140

20

40

60

80N

umbe

r of

indi

vidu

als


• The excessive use of antibiotics is leading to the evolution of antibiotic-resistant bacteria

– Example: Mycobacterium tuberculosis

Figure 13.22


• This is due to:

– historical constraints

– adaptive compromises

– chance events

– availability of variations

Natural selection cannot fashion perfect organisms


• appearance alone does not always define a species

Figure 14.1A

– Example: eastern and western meadowlarks

What is a species?

What is a species?

• Naturally interbreeding populations

- potentially interbreeding

- reproductively isolated from other species

What about asexually reproducing organisms?

Extinct species?

Shy species?


• When geographically isolated, species evolution may occur

– gene pool then changes to cause reproductive isolation

= allopatric speciation

When does speciation occur?

MECHANISMS OF SPECIATION

Figure 14.3


• A ring species may illustrate the process of speciation

Figure 14.1C

OREGONPOPULATION

1

2

COASTALPOPULATIONS

Yellow-eyed

Monterey3

SierraNevada

Yellow-blotched

Gap in ring Large-

blotched

INLANDPOPULATIONS


Reproductive barriers between species

• Habitat - different locations

• Timing - mating, flowering

• Behavioral - mating rituals, no attraction

• Mechanical - structural differences

• Gametic - fail to unite

• Hybrid weak or infertile


• Courtship ritual in blue-footed boobies is an example of behavioral isolation

• Many plant species have flower structures that are adapted to specific pollinators

– mechanical isolation

Figure 14.2A, B


• Hybrid sterility is one type of postzygotic barrier

– A horse and a donkey may produce a hybrid offspring, a mule

– Mules are sterile

Figure 14.2C


Sympatric speciation

• No geographical isolation

• Mutation creates reproductive isolation

• Polyploidization

• Hybridization

Mediumground finch

Cactusground finch

Smalltree finch

Largeground finch

Smallground finch

Large cactusground finch

Sharp-beakedground finch

Vegetarianfinch

Seedeaters

Ground finches

Cactus flowereaters

Budeaters

Tree finches

Insecteaters

Mediumtree finch

Largetree finch

Mangrovefinch

Woodpeckerfinch

Greenwarbler finch

Graywarbler finch

Warbler finches

Common ancestor fromSouth America mainland



• Specialists - Galapagos finches

• Generalists - horseshoe crabs, cockroaches

• New environments

- ecological niche



• Adaptive radiation on an island chain

- specialization for different niches

Figure 14.4B

Species Afrom mainland

1

A

2B

B

3BC 4

C

C5

BC

D

C D


• Continental drift is the slow, steady movement of Earth’s crustal plates on the hot mantle

Continental drift has played a major role in macroevolution

Figure 15.3A

PacificPlate

NorthAmerican

Plate

NazcaPlate

SouthAmerican

Plate

AfricanPlate

EurasianPlate

Splitdeveloping

Indo-AustralianPlate

Edge of one plate being pushed over edge of neighboring plate (zones of violent geologic events)

Antarctic Plate


• influenced the distribution of organisms

– Continental mergers triggered extinctions

– Separation of continents caused the isolation and diversification of organisms

Figure 15.3B

Mil

lio

ns

of

yea

rs a

go

EurasiaCE

NO

ZO

ICM

ES

OZ

OIC

PA

LE

OZ

OIC

North America

AfricaIndiaSouth

America

AntarcticaAustra

lia

Laurasia

Gondwana

Pangaea


Speciation - how much change is needed?

• Gradual vs. jerky

• Evidence:

– Fossil record

– Genetic differences between species

– Homeotic genes


• homeotic genes control body development

• Single mutation can result in major differences in body structure

Figure 11.14

Mouse chromosomes

Mouse embryo (12 days)

Adult mouse

Fly chromosomes

Fruit fly embryo (10 hours)

Adult fruit fly

Date post:	18-Jul-2015
Category:	Documents
Upload:	tauqeer-ahmad
View:	81 times
Download:	0 times

Macro evolution-natural-selection-speciation

Documents