SpeciationSpeciation

Proposing Mechanisms for Proposing Mechanisms for Species Formation and Species Formation and Identifying Ways to Maintain Identifying Ways to Maintain Reproductive IsolationReproductive Isolation

Two Types of Evolution Two Types of Evolution

Microevolution Microevolution

Macroevolution Macroevolution

Change within a Change within a population or species population or species

Change to a new Change to a new species species

Species FormationSpecies Formation

• Species = Group of actually or potentially Species = Group of actually or potentially interbreedinginterbreeding natural populations which natural populations which are are reproductively isolatedreproductively isolated from other from other such groupssuch groups

• Speciation depends onSpeciation depends on– isolation (lack of gene flow)isolation (lack of gene flow)– genetic divergencegenetic divergence

Mechanisms for SpeciationMechanisms for Speciation

• Allopatric SpeciationAllopatric Speciation– Occurs as a result of geographical isolationOccurs as a result of geographical isolation– Most common mechanismMost common mechanism

• Sympatric SpeciationSympatric Speciation– Occurs in the same locationOccurs in the same location– Can be due to Ecological isolationCan be due to Ecological isolation– Can be due to Polyploidy Can be due to Polyploidy

• Occurs for plants that have a sudden changeOccurs for plants that have a sudden change in numbers of chromosome sets in numbers of chromosome sets

Single species(white mice);homogeneous habitat

Geographical barrier(impassable river);isolated populations

Genetic drift;genetic divergence;

tan vs. white mice

Barrier removed(river dries up);

Mice mix but don’t interbreed.

Allopatric Speciation

(a)

(b)

(c)

(d)

Summary of Allopatric SpeciationSummary of Allopatric Speciation

• One group separates from the population.One group separates from the population.• Separate evolutionary pressures cause Separate evolutionary pressures cause

different genetic changes in both groups.different genetic changes in both groups. (Is this (1) microevolution or (2) macroevolution?)(Is this (1) microevolution or (2) macroevolution?)

• Sufficient genetic changes accumulate so Sufficient genetic changes accumulate so that interbreeding cannot occur if groups that interbreeding cannot occur if groups are rejoined. are rejoined.

(Is this (1) microevolution or (2) macroevolution?)(Is this (1) microevolution or (2) macroevolution?)

Genetic Divergence After Genetic Divergence After

Geographical IsolationGeographical Isolation

Four races of mole ratsFour races of mole rats show different numbers show different numbers of chromosomes of chromosomes Races live in areas withRaces live in areas with differing moisture content differing moisture content and soil type and soil type Hybrids rarely form Hybrids rarely form

Adaptive RadiationAdaptive Radiation

• One species gives rise to many new One species gives rise to many new species in a short period of timespecies in a short period of time– populations invade a variety of habitats and populations invade a variety of habitats and

evolve in response to differing evolve in response to differing environmental pressures in those habitatsenvironmental pressures in those habitats

– results fromresults from• availability of unoccupied habitats availability of unoccupied habitats • lack of competitionlack of competition

Sympatric Speciation

Single species(white mice);homogeneous habitat

(a)

Climate change;two habitats;isolated because don’t mix

(b)

Environmental pressure to adapt;genetic divergence;

tan vs. white mice

(c)

Sufficient divergence;

now different species

(d)

Speciation by Polyploidy

Chromosomes duplicatebut do not separateTetraploid with two sets of A and B.

Diploid with chromosome set A andchromosome set B.

Cross between diploid and tetraploid species Triploid with one each of chromosome sets A, B and D.

Chromosomes duplicate but do not separate Hexaploid with three sets of A, B and D.

Modern Wheat

Fertility of Polyploids

DiploidGamete

Meiosis

Meiosis

DiploidGametes

FertilizationViable Tetraploid

Zygote

DiploidGametes

HaploidGamete

Viable TriploidZygote

Meiosis(faulty)

Meiosis

Fertilization

Meiosis yields unbalanced products

no viable zygotes.

TetraploidPlant

TetraploidPlant

DiploidPlant

Applying Your KnowledgeApplying Your Knowledge

A.A. Which process involves a sudden, large Which process involves a sudden, large change in chromosome number?change in chromosome number?

B.B. Which process requires geographical Which process requires geographical separation?separation?

C.C. Which process can occur as a result of small Which process can occur as a result of small differences within the same local environment? differences within the same local environment?

1.1. Sympatric SpeciationSympatric Speciation2.2. Speciation by PolyploidySpeciation by Polyploidy3.3. Allopatric Speciation Allopatric Speciation

Maintaining Reproductive IsolationMaintaining Reproductive Isolation

• Premating Isolating MechanismsPremating Isolating Mechanisms– Prevent mating between individuals of Prevent mating between individuals of

different speciesdifferent species

• Postmating Isolating MechanismsPostmating Isolating Mechanisms– Interfere with development, viability or Interfere with development, viability or

fertility of offspring from matings between fertility of offspring from matings between speciesspecies

Premating Isolating Mechanism:Premating Isolating Mechanism:Geographical IsolationGeographical Isolation

The Grand Canyon is a geographical barrierThe Grand Canyon is a geographical barrier that can promote speciation. that can promote speciation. The Kaibab squirrel (left) lives on the The Kaibab squirrel (left) lives on the North Rim while the Avert squirrel (right) North Rim while the Avert squirrel (right) lives on the South Rim. lives on the South Rim.

Premating Isolating Mechanism:Premating Isolating Mechanism:Ecological IsolationEcological Isolation

White-throated SparrowWhite-throated Sparrowfeeds in dense thicketsfeeds in dense thickets

White-crowned SparrowWhite-crowned Sparrowinhabits fields and meadowsinhabits fields and meadows

Premating Isolating Mechanism:Premating Isolating Mechanism:Ecological IsolationEcological Isolation

Each of the 750 species of Each of the 750 species of fig wasps pollinates a fig wasps pollinates a different species of fig plant. different species of fig plant.

Premating Isolating Mechanism:Premating Isolating Mechanism:Temporal IsolationTemporal Isolation

Premating Isolating Premating Isolating Mechanism:Mechanism:

Temporal IsolationTemporal Isolation

Bishop’s Pine releases Bishop’s Pine releases pollen in summerpollen in summer

Monterey Pine releasesMonterey Pine releases pollen in early spring pollen in early spring

Premating Isolating Mechanism:Premating Isolating Mechanism:Temporal IsolationTemporal Isolation

Periodic Cicada: Males emergePeriodic Cicada: Males emergeon a 13 or 17-year cycle. on a 13 or 17-year cycle.

Premating Isolating Mechanism: Premating Isolating Mechanism: Behavioral IsolationBehavioral Isolation

Firefly signaling patterns Firefly signaling patterns differ between speciesdiffer between species

Fruit fly species have Fruit fly species have

different wing beat different wing beat frequencies for the frequencies for the mating ritual. mating ritual.

Premating Isolating Mechanism: Premating Isolating Mechanism:

Behavioral IsolationBehavioral Isolation

White-crowned sparrows from different areas White-crowned sparrows from different areas have distinct song patterns for territorial displays.have distinct song patterns for territorial displays.

Premating Isolating MechanismPremating Isolating Mechanism

MechanismMechanism ExamplesExamples

Mechanical Isolation:Mechanical Isolation:differences in structure of sexual differences in structure of sexual organsorgans

-Male sex organs of separate-Male sex organs of separate insect species vary greatly insect species vary greatly-Pollen from one plant species -Pollen from one plant species does not germinate on female does not germinate on female part of another species part of another species

female

clasper

Postmating Isolating MechanismPostmating Isolating Mechanism

MechanismMechanism ExampleExample

Gametic Gametic IncompatibilityIncompatibility

--Sperm may not have the proper Sperm may not have the proper enzymes to remove the egg’s enzymes to remove the egg’s protective coat protective coat

- Pollen may not be able to grow - Pollen may not be able to grow toward the egg in plants of different toward the egg in plants of different species species

Postmating Isolating Mechanism: Postmating Isolating Mechanism:

Hybrid InviabilityHybrid Inviability

Hybrids between Sheep and Goats Hybrids between Sheep and Goats do not survive do not survive

Postmating Isolating Mechanism: Postmating Isolating Mechanism: Hybrid InfertilityHybrid Infertility

horse +horse + donkeydonkey

MuleMuleCannot ReproduceCannot Reproduce

Postmating Isolating Mechanism: Postmating Isolating Mechanism: Hybrid BreakdownHybrid Breakdown

LigerLigerTiglionTiglion

Hybrids of Lions and Tigers have been obtainedHybrids of Lions and Tigers have been obtainedthrough zoo breeding programs. While the first through zoo breeding programs. While the first generation may be healthy, hybrids become weak generation may be healthy, hybrids become weak or sterile in future generations. or sterile in future generations.

Applying Your KnowledgeApplying Your Knowledge

A.A. Hybrids of dogs and wolves can occur. Some Hybrids of dogs and wolves can occur. Some have more dog traits and others favor wolves. have more dog traits and others favor wolves. After two or more generations, the hybrids are After two or more generations, the hybrids are feeble and cannot reproduce.feeble and cannot reproduce.

B.B. The male fruit fly flaps his wing to attract a The male fruit fly flaps his wing to attract a nearby female. Wing beat frequencies differ nearby female. Wing beat frequencies differ between species so a female will only accept between species so a female will only accept the male that has the correct wing beat. the male that has the correct wing beat.

1.1. Premating Isolating MechanismPremating Isolating Mechanism2.2. Postmating Isolating MechanismPostmating Isolating Mechanism

Applying Your KnowledgeApplying Your Knowledge

A.A. English Oak is found in Europe and Scrub Oak is English Oak is found in Europe and Scrub Oak is found in California. found in California.

B.B. Lions live in groups called prides on open grassland. Lions live in groups called prides on open grassland. Tigers are solitary and live in forests. These species Tigers are solitary and live in forests. These species do not form hybrids even though their ranges do not form hybrids even though their ranges overlap. overlap.

C.C. The male Reggiana bird of paradise displays his The male Reggiana bird of paradise displays his feathers to a potential mate. The female trumpet feathers to a potential mate. The female trumpet manucode, a related species, is not attracted by this manucode, a related species, is not attracted by this display. display.

1.1. Temporal IsolationTemporal Isolation2.2. Ecological IsolationEcological Isolation3.3. Behavioral IsolationBehavioral Isolation4.4. Geographical IsolationGeographical Isolation5.5. Mechanical IsolationMechanical Isolation

ExtinctionExtinction

Death of all members of a speciesFactors that contribute to extinction

localized distribution of a speciesoverspecialization competitionhabitat change and destruction

Localized Species DistributionLocalized Species Distribution

The Devil’s Hole PupfishThe Devil’s Hole Pupfish lives in a single pool at lives in a single pool at the mouth of a water-filled the mouth of a water-filled cave system in Nevada. cave system in Nevada.

OverspecializationOverspecialization

The Everglades Kite depends on a single species of snail as a food source.