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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 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.