Speciation and Speciation and MacroevolutionMacroevolution

Chapter 20Chapter 20

Learning Objective 1Learning Objective 1

• What is the What is the biological species conceptbiological species concept??

• List two potential problems with the List two potential problems with the conceptconcept

Biological Species ConceptBiological Species Concept

• SpeciesSpecies• one or more populationsone or more populations• members interbreed in naturemembers interbreed in nature• produce fertile offspringproduce fertile offspring• do not interbreed with different speciesdo not interbreed with different species

Sterile HybridSterile Hybrid

ProblemsProblems

• Biological species conceptBiological species concept applies only to applies only to sexually reproducing organismssexually reproducing organisms

• Individuals assigned to different species Individuals assigned to different species may occasionally successfully interbreedmay occasionally successfully interbreed

KEY CONCEPTSKEY CONCEPTS

• According to the biological species According to the biological species concept, a species consists of individuals concept, a species consists of individuals that can successfully interbreed with one that can successfully interbreed with one another but not with individuals from other another but not with individuals from other speciesspecies

Learning Objective 2Learning Objective 2

• What is the significance of What is the significance of reproductive reproductive isolating mechanismsisolating mechanisms??

• Distinguish among different Distinguish among different prezygoticprezygotic and and postzygotic barrierspostzygotic barriers

Reproductive Isolating MechanismsReproductive Isolating Mechanisms

• Restrict gene flow between speciesRestrict gene flow between species

• Prezygotic barriersPrezygotic barriers• prevent fertilization from taking place prevent fertilization from taking place

• Postzygotic barriersPostzygotic barriers• prevent gene flow after fertilization has taken prevent gene flow after fertilization has taken

place (reproductive isolating mechanisms)place (reproductive isolating mechanisms)

Prezygotic Barriers (1)Prezygotic Barriers (1)

• Temporal isolationTemporal isolation• two species reproduce at different times of two species reproduce at different times of

day, season, or year day, season, or year

• Habitat isolationHabitat isolation• two closely related species live and breed in two closely related species live and breed in

different habitats in same geographic area different habitats in same geographic area

Temporal IsolationTemporal Isolation

Fig. 20-2a, p. 430

Fig. 20-2b, p. 430

Fig. 20-2c, p. 430

Wood frog

Leopard frog

Mat

ing

act

ivit

y

March 1 April 1 May 1

Insert “Temporal isolation Insert “Temporal isolation among cicadas”among cicadas”

temporal_isolation.swftemporal_isolation.swf

Prezygotic Barriers (2)Prezygotic Barriers (2)

• Behavioral isolationBehavioral isolation• distinctive courtship behaviors prevent mating distinctive courtship behaviors prevent mating

between species between species

• Mechanical isolationMechanical isolation• incompatible structural differences in incompatible structural differences in

reproductive organs of similar speciesreproductive organs of similar species

Behavioral IsolationBehavioral Isolation

Mechanical IsolationMechanical Isolation

Prezygotic Barriers (3)Prezygotic Barriers (3)

• Gametic isolationGametic isolation• gametes from different species are gametes from different species are

incompatible because of molecular and incompatible because of molecular and chemical differenceschemical differences

Postzygotic Barriers (1)Postzygotic Barriers (1)

• Hybrid inviabilityHybrid inviability• interspecific embryos die during developmentinterspecific embryos die during development

• Hybrid sterilityHybrid sterility• prevents interspecific hybrids that survive to prevents interspecific hybrids that survive to

adulthood from reproducing successfullyadulthood from reproducing successfully

Hybrid SterilityHybrid Sterility

Postzygotic Barriers (2)Postzygotic Barriers (2)

• Hybrid breakdownHybrid breakdown• prevents offspring of hybrids that survive to prevents offspring of hybrids that survive to

adulthood and successfully reproduce from adulthood and successfully reproduce from reproducing beyond one or a few generationsreproducing beyond one or a few generations

KEY CONCEPTSKEY CONCEPTS

• The evolution of different species begins The evolution of different species begins with reproductive isolation, in which two with reproductive isolation, in which two populations are no longer able to populations are no longer able to interbreed successfullyinterbreed successfully

Insert “Reproductive Insert “Reproductive isolating mechanisms”isolating mechanisms”

isolating_mechanisms_m.swfisolating_mechanisms_m.swf

Explore reproductive isolation by Explore reproductive isolation by clicking on the figures in clicking on the figures in

ThomsonNOWThomsonNOW

Learning Objective 3Learning Objective 3

• What is What is allopatric speciationallopatric speciation??

• Give an exampleGive an example

Allopatric Speciation (1)Allopatric Speciation (1)

• Evolution of a new Evolution of a new speciesspecies• from ancestral populationfrom ancestral population

• Population becomes geographically Population becomes geographically isolated from rest of speciesisolated from rest of species

• subsequently diverges subsequently diverges

Allopatric Speciation (2)Allopatric Speciation (2)

• More likely to occur if original isolated More likely to occur if original isolated population is smallpopulation is small

• makes genetic drift more significantmakes genetic drift more significant

• Examples:Examples:• Death Valley pupfishesDeath Valley pupfishes• Kaibab squirrelsKaibab squirrels• Porto Santo rabbitsPorto Santo rabbits

Allopatric SpeciationAllopatric Speciation

KEY CONCEPTSKEY CONCEPTS

• In allopatric speciation, populations In allopatric speciation, populations diverge into different species due to diverge into different species due to geographic isolation, or physical geographic isolation, or physical separationseparation

Insert “Allopatric speciation Insert “Allopatric speciation on an archipelago”on an archipelago”

archipelago.swfarchipelago.swf

Explore allopatric speciation by Explore allopatric speciation by clicking on the figures in clicking on the figures in

ThomsonNOW.ThomsonNOW.

Learning Objective 4Learning Objective 4

• What is What is sympatric speciationsympatric speciation??

• Give plant and animal examplesGive plant and animal examples

Sympatric SpeciationSympatric Speciation

• Does not require geographic isolationDoes not require geographic isolation

• More common in plants than animalsMore common in plants than animals

Sympatric Speciation in PlantsSympatric Speciation in Plants

• Usually results from Usually results from allopolyploidyallopolyploidy• polyploidpolyploid individual (>2 sets of chromosomes) individual (>2 sets of chromosomes)

is hybrid derived from two speciesis hybrid derived from two species

• Examples:Examples:• kew primroseskew primroses• hemp nettleshemp nettles

Allopolyploidy Allopolyploidy in Plantsin Plants

Fig. 20-9a, p. 435

Species A Species B

P generation

n = 3 n = 2

Gametes

Hybrid AB

F1 generation

2 n = 6 2 n = 4

Fig. 20-9b, p. 435

No doubling of chromosome number

Doubling of chromosome number

2 n = 10

Chromosomes either cannot pair or go

through erratic meiosis

Pairing now possible

during meiosisn = 5

No gametes or sterile gametes — no sexual reproduction possible

Viable gametes — sexual reproduction possible (self-

fertilization)

Fig. 20-9b, p. 435

Stepped ArtNo gametes or sterile gametes — no sexual reproduction possible

Pairing now possible

during meiosis

n = 5

Viable gametes — sexual reproduction possible (self-

fertilization)

No doubling of chromosome number

Chromosomes either cannot pair or go through

erratic meiosis

Doubling of chromosome number

2 n = 10

n = 3 n = 2Gametes

Hybrid AB

F1 generation

Species A Species B

P generation

2 n = 6 2 n = 4

Sympatric SpeciationSympatric Speciation

Sympatric Speciation in AnimalsSympatric Speciation in Animals

• Fruit maggot fliesFruit maggot flies

Sympatric Speciation in AnimalsSympatric Speciation in Animals

• CichlidsCichlids

Fig. 20-12a, p. 437

Fig. 20-12b, p. 437

Fig. 20-12c, p. 437

KEY CONCEPTSKEY CONCEPTS

• In sympatric speciation, populations In sympatric speciation, populations become reproductively isolated from one become reproductively isolated from one another despite living in the same another despite living in the same geographic areageographic area

Insert “Sympatric Insert “Sympatric speciation in wheat”speciation in wheat”

wheat_speciation.swfwheat_speciation.swf

Explore sympatric speciation by Explore sympatric speciation by clicking on the figure in clicking on the figure in

ThomsonNOW.ThomsonNOW.

Learning Objective 5Learning Objective 5

• Debate the pace of evolution by Debate the pace of evolution by representing the views of either representing the views of either punctuated equilibriumpunctuated equilibrium or or gradualismgradualism

EvolutionEvolution

• Punctuated equilibriumPunctuated equilibrium model model• evolution proceeds in spurtsevolution proceeds in spurts• short periods of active speciation short periods of active speciation

interspersed with long periods of interspersed with long periods of stasisstasis

• GradualismGradualism model model• populations slowly diverge from one another populations slowly diverge from one another

by accumulation of adaptive characteristicsby accumulation of adaptive characteristics

Punctuated EquilibriumPunctuated Equilibrium and Gradualism and Gradualism

Fig. 20-13, p. 438

Extinction of original species

Stasis

Slow, gradual changes

Stasis

Stasis

Time Divergence is sudden, with rapid changes

Time

Divergence is gradual

Stasis (little change)

Structural changes Structural changes

KEY CONCEPTSKEY CONCEPTS

• Speciation may require millions of years Speciation may require millions of years but sometimes occurs much more quicklybut sometimes occurs much more quickly

Learning Objective 6Learning Objective 6

• What is What is macroevolutionmacroevolution??

MacroevolutionMacroevolution

• Large-scale phenotypic changes in Large-scale phenotypic changes in populationspopulations

• in taxonomic groups species level and higherin taxonomic groups species level and higher• new species, genera, families, orders, new species, genera, families, orders,

classes, phyla, kingdoms, or domainsclasses, phyla, kingdoms, or domains

KEY CONCEPTSKEY CONCEPTS

• The evolution of species and higher taxa is The evolution of species and higher taxa is known as macroevolutionknown as macroevolution

Learning Objective 7Learning Objective 7

• Discuss novel features of macroevolution, Discuss novel features of macroevolution, including including preadaptationspreadaptations, , allometric allometric growthgrowth, and , and paedomorphosispaedomorphosis

MacroevolutionMacroevolution

• Includes Includes evolutionary noveltiesevolutionary novelties• due to changes during due to changes during development development

• Slight changes in regulatory genesSlight changes in regulatory genes• cause major structural changes in organism cause major structural changes in organism

PreadaptationsPreadaptations

• Structures originally fulfilled one roleStructures originally fulfilled one role• changed and adapted for different role changed and adapted for different role

• Example:Example: feathersfeathers

Allometric GrowthAllometric Growth

• Varied rates of growth for different parts of Varied rates of growth for different parts of bodybody

• causes overall changes in shape of organismcauses overall changes in shape of organism

• Examples:Examples:• ocean sunfishocean sunfish• male fiddler crabmale fiddler crab

Allometric GrowthAllometric Growth

• Ocean sunfishOcean sunfish

Fig. 20-14a, p. 440

Tail

approx. 1 mm

Newly hatched ocean sunfish

Adult ocean sunfish

Fig. 20-14b, p. 440

Fig. 20-14b, p. 440

PaedomorphosisPaedomorphosis

• Juvenile characteristics retained in adultJuvenile characteristics retained in adult• due to changes in timing of development due to changes in timing of development

• Example: adult axolotl salamandersExample: adult axolotl salamanders• with external gills and tail finswith external gills and tail fins

PaedomorphosisPaedomorphosis

• SalamanderSalamander

Learning Objective 8Learning Objective 8

• What is the macroevolutionary significance What is the macroevolutionary significance of of adaptive radiationadaptive radiation and and extinctionextinction??

Adaptive Radiation (1)Adaptive Radiation (1)

• Diversification of ancestral species into Diversification of ancestral species into many new species many new species

• Adaptive zonesAdaptive zones• new ecological opportunities not exploited by new ecological opportunities not exploited by

ancestral organism ancestral organism

Adaptive Radiation (2)Adaptive Radiation (2)

• When many adaptive zones are emptyWhen many adaptive zones are empty• colonizing species diversify and exploit them colonizing species diversify and exploit them

• Example: Hawaiian honeycreepers and Example: Hawaiian honeycreepers and silverswordssilverswords

• after ancestors colonized Hawaiian Islandsafter ancestors colonized Hawaiian Islands

Adaptive RadiationAdaptive Radiation

• Hawaiian honeycreepersHawaiian honeycreepers

Fig. 20-16, p. 441

Rips away bark to find insects Kauai Sips flower nectarMaui parrot bill ‘I‘iwi

Oahu Forages among leaves and branches

Maui creeper

Chisels holes in bark to get insects

Maui Extinct Habits unknown

Akiapolaau Ula-ai-hawane

Extinct Sipped flower nectar Hawaii

Black mamo

Picks food from cracks in the bark Sips flower nectarAkialoa Apapane

Feeds on snails and invertebrates Sips flower nectarPoo-uli Crested honeycreeper

Adaptive RadiationAdaptive Radiation

• Hawaiian silverswordsHawaiian silverswords

Extinction (1)Extinction (1)

• Death of a species Death of a species

• When species become extinctWhen species become extinct• adaptive zones they occupied become vacantadaptive zones they occupied become vacant• allows other species to evolve and fill zones allows other species to evolve and fill zones

Extinction (2)Extinction (2)

• Background extinctionBackground extinction• continuous, low-level extinction of speciescontinuous, low-level extinction of species

• Mass extinctionMass extinction• extinction of numerous species, higher extinction of numerous species, higher

taxonomic groupstaxonomic groups• in both terrestrial and marine environmentsin both terrestrial and marine environments

Mass Mass ExtinctionExtinction

Fig. 20-18a, p. 443

Cro

cod

ilia

ns

(all

igat

ors

, cr

oco

dil

es)

Orn

ith

isch

ian

s (d

ino

sau

rs,

exti

nct

)

Sau

risc

hia

ns

(din

osa

urs

, ex

tin

ct)

Bir

ds

Common ancestor of birds and saurischians

Archosaur common ancestor

Pte

rosa

urs

(f

lyin

g r

epti

les,

ex

tin

ct)

Fig. 20-18b, p. 443

Fig. 20-18b, p. 443

Paleozoic Mesozoic CenozoicPermian Triassic Jurassic Cretaceous Tertiary / Quaternary

Theropods (carnivorous saurischians) Birds

Archosaurs Sauropods (herbivorous saurischians)

Common ancestor

Stegosaurs and other

ornithischians

PterosaursCrocodilians Crocodiles