Evolutionary MechanismsEvolutionary Mechanisms

Chapter 15Chapter 15

Pages 428 - 441Pages 428 - 441

Warm-up QuestionWarm-up Question• According to the theory of natural selection, According to the theory of natural selection,

why are some individuals more likely than why are some individuals more likely than others to survive and reproduce?others to survive and reproduce?

A. They pass on to their offspring new A. They pass on to their offspring new characteristics they acquired during their characteristics they acquired during their lifetime.lifetime.

B. They are better adapted to exist in their B. They are better adapted to exist in their environment than others.environment than others.

C. They tend to produce fewer offspring than do C. They tend to produce fewer offspring than do others in the same environment.others in the same environment.

AdaptationsAdaptations• The heart of Darwin’s Theory of Natural The heart of Darwin’s Theory of Natural

SelectionSelection– Organisms adapt to their environment through Organisms adapt to their environment through

slow change over time.slow change over time.– Variations in genes give rise to adaptations.Variations in genes give rise to adaptations.

• adaptationsadaptations – traits that help organisms – traits that help organisms survive in the environment in which they survive in the environment in which they live.live.

• FitnessFitness – a measure of the contributions an – a measure of the contributions an individual trait makes to the survival of the individual trait makes to the survival of the next generation.next generation.

Environments ChangeEnvironments Change

• Peppered Moths ExamplePeppered Moths Example

• Mid 18Mid 18thth century = England’s century = England’s industrial revolution resulted in tons industrial revolution resulted in tons of soot deposited on trees and rocks.of soot deposited on trees and rocks.

• The discoloration camouflaged dark The discoloration camouflaged dark colored moths.colored moths.

• Where these dark colored moths Where these dark colored moths were once the minority, they are now were once the minority, they are now the majority.the majority.

Types of AdaptationTypes of Adaptation

1. 1. CamouflageCamouflage – allows organisms to – allows organisms to become almost invisible to predators. become almost invisible to predators. (cuttlefish) (cuttlefish)

2. 2. MimicryMimicry – a species evolves to – a species evolves to resemble another species.resemble another species.• Often increases an organisms fitness Often increases an organisms fitness

because the harmless species looks because the harmless species looks like the harmful one so predators will like the harmful one so predators will stay away. stay away.

5 Mechanisms of Evolution:5 Mechanisms of Evolution:

1.1. Natural selection – Natural selection – is not the only is not the only mechanism of evolutionmechanism of evolution

2.2. Genetic DriftGenetic Drift• Founder EffectFounder Effect• BottleneckBottleneck

3.3. Gene FlowGene Flow

4.4. Nonrandom MatingNonrandom Mating

5.5. MutationsMutations

Population Genetics

The Gene PoolThe Gene Pool• Gene PoolGene Pool – all of the genes present in – all of the genes present in

a populationa population

• Sources of Variation in a Gene PoolSources of Variation in a Gene Pool::1. Two copies of chromosomes present in 1. Two copies of chromosomes present in

each celleach cell

2. Mutations create new alleles2. Mutations create new alleles

3. Other events cause a shuffling of genes 3. Other events cause a shuffling of genes into into different combinations:different combinations:

a. crossing overa. crossing over

b. random assortment (see next slide)b. random assortment (see next slide)

c. and fertilizationc. and fertilization

Random AssortmentRandom Assortment

Breeding Bunnies Activity Breeding Bunnies Activity TodayToday• Work in PAIRS! NO MORE THAN 2!!!Work in PAIRS! NO MORE THAN 2!!!

• 50 red beans50 red beans

• 50 white beans50 white beans

• 1 large container for breeding1 large container for breeding

• 1 waste container for the alleles of dead1 waste container for the alleles of dead

bunnies bunnies • Instruction SheetInstruction Sheet

• Data Sheet and Discussion QuestionsData Sheet and Discussion Questions

• Graph PaperGraph Paper

Population GeneticsPopulation Genetics

• Hardy & WeinbergHardy & Weinberg (1908) (1908) – showed – showed that evolution will not occur in a that evolution will not occur in a population unless allelic frequencies population unless allelic frequencies are acted upon by forces that cause are acted upon by forces that cause change.change.

• Hardy-Weinberg PrincipleHardy-Weinberg Principle – when – when allelic frequencies remain constant, a allelic frequencies remain constant, a population is in population is in genetic equilibriumgenetic equilibrium..

Hardy-Weinberg Principle Hardy-Weinberg Principle Conditions – Conditions –

Equilibrium exists and evolution does not occur Equilibrium exists and evolution does not occur if:if:

Population is very largePopulation is very large No immigration or emigrationNo immigration or emigration Mating is randomMating is random Mutations do not occurMutations do not occur Natural selection does not occurNatural selection does not occurPopulations rarely meet these requirements for long periods of time.

http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flash/life4e_15-6-OSU.swf

Hardy-Weinberg EquationHardy-Weinberg Equation

Each genotype has two alleles, p and Each genotype has two alleles, p and q.q.

(p + q)(p + q)22 = 1 = 1

pp22 + + 22pq + qpq + q22 = 1 = 1 p q

p

q

Genetic DriftGenetic Drift• Any change in the allelic frequencies Any change in the allelic frequencies

in a population that is due to chance.in a population that is due to chance.

• In large populations, enough alleles In large populations, enough alleles “drift” to insure that the allelic “drift” to insure that the allelic frequency of the entire population frequency of the entire population remains relatively constant from one remains relatively constant from one generation to the next.generation to the next.

• In smaller populations, however, the In smaller populations, however, the effects of genetic drift become more effects of genetic drift become more pronounced, and the chance of losing pronounced, and the chance of losing an allele becomes greater.an allele becomes greater.

Two Kinds of Genetic Drift:Two Kinds of Genetic Drift:1.1. The Founder EffectThe Founder Effect (an extreme (an extreme

example of genetic drift)example of genetic drift)- Can occur when a small sample of a Can occur when a small sample of a

population settles in a location population settles in a location separated from the rest of the separated from the rest of the population. population.

- ExampleExample: Amish and Mennonite : Amish and Mennonite communities in the U.S. have a high communities in the U.S. have a high frequency of six-finger dwarfism.frequency of six-finger dwarfism.

2.2. Bottleneck Bottleneck (another extreme (another extreme example of genetic drift)example of genetic drift)

• Occurs when a population declines to Occurs when a population declines to a very low number and then a very low number and then rebounds.rebounds.

• The gene pool of the rebounded The gene pool of the rebounded population now has reduced population now has reduced diversity.diversity.

Gene FlowGene Flow

• The random movement of individuals The random movement of individuals between populations (migration) between populations (migration) increases genetic variation within a increases genetic variation within a population and reduces differences population and reduces differences between populations.between populations.

Nonrandom MatingNonrandom Mating

• Usually, organisms mate with Usually, organisms mate with individuals within close proximity. individuals within close proximity. This promotes inbreeding and could This promotes inbreeding and could lead to a change in allelic proportions lead to a change in allelic proportions favoring individuals that are favoring individuals that are homozygous for particular traits.homozygous for particular traits.

MutationMutation

• A random change in genetic materialA random change in genetic material

• Provides the raw material upon Provides the raw material upon which natural selection works:which natural selection works:– Occasionally, a mutation provides an Occasionally, a mutation provides an

advantage to an organism. This advantage to an organism. This mutation will then be selected for and mutation will then be selected for and become more common in subsequent become more common in subsequent generations.generations.

Natural SelectionNatural Selection• Acts to select the individuals that are best Acts to select the individuals that are best

adapted for survival and reproduction.adapted for survival and reproduction.

• Acts on an organism’s phenotype and Acts on an organism’s phenotype and changes allelic frequencies in four changes allelic frequencies in four ways:ways:1. through Stabilizing Selection1. through Stabilizing Selection

2. Directional Selection2. Directional Selection

3. Disruptive Selection, and3. Disruptive Selection, and

4. Sexual Selection4. Sexual Selection

http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flash/life4e_15-6-OSU.swf

1. Stabilizing Selection:

2. Directional Selection:

3. Disruptive Selection:

4. 4. Sexual SelectionSexual Selection

• Males are larger and more colorful Males are larger and more colorful than females.than females.

• Brighter colors and bigger bodies Brighter colors and bigger bodies enhance reproductive success.enhance reproductive success.

http://video.nationalgeographic.com/video/player/animals/birds-animals/seabirds/boobies_bluefooted.html

http://www.youtube.com/watch?v=T2Bsu4z9Y3k&safety_mode=true&persist_safety_mode=1&safe=active

SpeciationSpeciationWhen some members of a population When some members of a population

become separated from the group become separated from the group and change so much that they can and change so much that they can no longer mate with members of the no longer mate with members of the original population.original population.

2 Types2 Types::

1. Allopatric Speciation1. Allopatric Speciation

2. Sympatric Speciation2. Sympatric Speciation

1. Allopatric Speciation1. Allopatric Speciation

• The most common form of speciationThe most common form of speciation• A physical barrier divides a A physical barrier divides a

population into two (or more) population into two (or more) populations. Over time, the populations. Over time, the populations will change until populations will change until eventually they are no longer able to eventually they are no longer able to breed with one another.breed with one another.

2. Sympatric Speciation2. Sympatric Speciation

• When a species evolves into a new When a species evolves into a new species without a physical barrier.species without a physical barrier.

• Occurs most commonly among Occurs most commonly among plants through polyploidy (a plants through polyploidy (a mutation that increases a plant’s mutation that increases a plant’s chromosome number).chromosome number).

Patterns of EvolutionPatterns of Evolution

1.1. Adaptive RadiationAdaptive Radiation

2.2. CoevolutionCoevolution

3.3. Convergent EvolutionConvergent Evolution

1. Adaptive Radiation1. Adaptive Radiation

• Also called divergent evolutionAlso called divergent evolution

• Can occur in a relatively short period Can occur in a relatively short period of time.of time.

• When one species gives rise to many When one species gives rise to many in response to the creation of a new in response to the creation of a new habitat or another ecological habitat or another ecological opportunity.opportunity.

• Example = cichlid fishesExample = cichlid fishes

2. Co-evolution2. Co-evolution• Many species evolve in close Many species evolve in close

relationship with other species.relationship with other species.

• The evolution of one species can affect The evolution of one species can affect the evolution of another species.the evolution of another species.

• Example = comet orchids and the Example = comet orchids and the moths that pollinate them. The foot-moths that pollinate them. The foot-long flowers of this plant perfectly long flowers of this plant perfectly match the foot-long tongue of the match the foot-long tongue of the moth.moth.

3. Convergent Evolution3. Convergent Evolution

• When unrelated species evolve When unrelated species evolve similar traits even though they live in similar traits even though they live in different parts of the world.different parts of the world.

• Occurs in environments that are Occurs in environments that are geographically far apart but that geographically far apart but that have similar ecology and climate.have similar ecology and climate.

Example for convergent evolution: