D2: Species and SpeciationD2: Species and Speciation

5 hours5 hours

D.2.1D.2.1 Define allele frequency, gene pool.Define allele frequency, gene pool.

• Allele frequencyAllele frequency– % of certain allele (variation of a % of certain allele (variation of a

gene) in the population for a certain gene) in the population for a certain locus/genelocus/gene

• Gene poolGene pool– All genetic info of reproducing All genetic info of reproducing

members of the populationmembers of the population– VariationVariation

D.2.2D.2.2 State that evolution involves a change in State that evolution involves a change in allele frequency in a population’s gene pool over a allele frequency in a population’s gene pool over a number of generations.number of generations.

• Mutation introduces new allelesMutation introduces new alleles• Old alleles “die out”Old alleles “die out”• Advantageous Advantageous survives survives

• Change in allele freq = evolutionChange in allele freq = evolution– SEVERAL generations!SEVERAL generations!

D.2.3D.2.3 Discuss the definition of the term species.Discuss the definition of the term species.Xref- species- 5.1.1Xref- species- 5.1.1

• Organisms have similar physiological Organisms have similar physiological and morphological characteristicsand morphological characteristics

• Ability to interbreed, produce fertile Ability to interbreed, produce fertile offspringoffspring

• Genetically distinct from other Genetically distinct from other speciesspecies

• Common phylogenyCommon phylogeny

• Not exactly that simple, but good Not exactly that simple, but good enough for now!enough for now!

D.2.4D.2.4 Describe three examples of barriers between Describe three examples of barriers between gene pools. Examples include gene pools. Examples include

• SEPARATE POPULATIONS...MAY LEAD TO SEPARATE POPULATIONS...MAY LEAD TO SPECIATIONSPECIATION

• geographical isolationgeographical isolation– Physical barriers (land, water formation) prevent Physical barriers (land, water formation) prevent

males/females from meeting & interbreeding—males/females from meeting & interbreeding—populations are separatedpopulations are separated

• hybrid infertilityhybrid infertility– 22ndnd generation unlikely generation unlikely– Genetic barrier between speciesGenetic barrier between species

• temporal isolationtemporal isolation– Incompatible time frames for mating (flowers Incompatible time frames for mating (flowers

blooming/seasons; hibernations; migrations)blooming/seasons; hibernations; migrations)

• behavioural isolationbehavioural isolation– Lifestyle, habits incompatible with other populationLifestyle, habits incompatible with other population– Courtship displaysCourtship displays

D.2.5D.2.5 Explain how polyploidy can contribute to Explain how polyploidy can contribute to speciation.speciation.Xref- Meiosis- 4.2.3 / 10.1Xref- Meiosis- 4.2.3 / 10.1

• Avoid examples involving hybridization Avoid examples involving hybridization as well as polyploidy, such as the as well as polyploidy, such as the evolution of wheat. evolution of wheat.

• 3n, 4n, 5n, etc.3n, 4n, 5n, etc.• Cell division mistakes, chromosomes Cell division mistakes, chromosomes

don’t separate completelydon’t separate completely• Common in plantsCommon in plants• Extra chroms Extra chroms plant more vigorous plant more vigorous• Replication errors more commonReplication errors more common• 2 populations could evolve at different 2 populations could evolve at different

rates b/c of difference in ploidyrates b/c of difference in ploidy• Could lead to speciationCould lead to speciation

D.2.6D.2.6 Compare allopatric speciation, sympatric Compare allopatric speciation, sympatric speciation.speciation.• Speciation: the formation of a new Speciation: the formation of a new

species by splitting of an existing species by splitting of an existing species.species.

• Sympatric: in the same geographical Sympatric: in the same geographical area—area—Temporal, behavioural isolationTemporal, behavioural isolation– Pheromones, mating calls, etc. may be Pheromones, mating calls, etc. may be

changed slightly, allow for mates or notchanged slightly, allow for mates or not

• Allopatric: in different geographical Allopatric: in different geographical areas—geographic isolation areas—geographic isolation – 2 pops separated, evolve separately– If allowed to mingle in future, may not be

able to interbreed...new species

SawFly (Tenthredo livida)

Snow geese (Chen caerulescens)

Pin and thrumb primroses (Primula vulgaris) Fertilisation

Zedonk

Genetic

Hybrid inviability• Hybrid offspring

die• Hybrid infertility

Hybrids survive but are incapable of producing gametes

D.2.7D.2.7 Outline the process of adaptive radiation.Outline the process of adaptive radiation.

• ““Rapid” evolution from 1 (or a few) Rapid” evolution from 1 (or a few) species into morespecies into more

• Slightly diff niches, more successfulSlightly diff niches, more successful• Natural selectionNatural selection• Speciation event(s) (isolation)Speciation event(s) (isolation)• EX-finches, lemursEX-finches, lemurs• Lemurs once widespread b/c no Lemurs once widespread b/c no

competition (apes, monkeys)competition (apes, monkeys)– Lots phenotypic diversityLots phenotypic diversity– Some better adapted to certain niches, led to Some better adapted to certain niches, led to

adaptive radiationadaptive radiation– Apes, monkeys...outcompete lemurs, so Apes, monkeys...outcompete lemurs, so

lemurs not found lemurs not found

Mechanisms of speciation

Isolation of a population so that it cannot breed freely with others is necessary

Geographic Ecological Behavioural Mechanical/

anatomical Physiological Genetic

Madagascar Google earth

Ringtailed lemurs

(Lemur catta)

© 2008 Paul Billiet ODWS

D.2.8D.2.8 Compare convergent evolution, divergent Compare convergent evolution, divergent evolution.evolution.

• Convergent– Not a recent common ancestor – 2 species or characteristics look

similar– Australia & N America: marsupials vs

placentals– Wings (bat, bird); bioluminescence

(bacteria, fungi)

• Divergent – Recent common ancestor– Less similar over time

D.2.9D.2.9 Discuss ideas on the pace of evolution Discuss ideas on the pace of evolution including gradualism and punctuated equilibrium.including gradualism and punctuated equilibrium.

• Gradualism: small, continuous, slow Gradualism: small, continuous, slow change from one form to anotherchange from one form to another– Fossil recordFossil record– Present day examplesPresent day examples– P. 429 diagramsP. 429 diagrams

• Punctuated equilibrium: long periods Punctuated equilibrium: long periods without appreciable change and short without appreciable change and short periods of rapid evolutionperiods of rapid evolution– Response to change in environmentResponse to change in environment

• Volcanic eruptions and meteor impacts Volcanic eruptions and meteor impacts affecting evolution on Earthaffecting evolution on Earth

– 65mya...dinosaurs extinct; mammals 65mya...dinosaurs extinct; mammals survivedsurvived

– Until a big environmental change, little/no Until a big environmental change, little/no change in fossil recordchange in fossil record

Evolution of new species Two possible ways from gradualism PHYLETIC TRANSFORMATION ALLOPATRIC SPECIATION

© 2008 Paul Billiet ODWS

PHYLETIC TRANSFORMATION

Gradual accumulation of small genetic variations preserved by natural selection

A whole population imperceptibly to evolve in to a new species

Impossible to draw a clear line between the end of the first species and the beginning of its descendant species

There would be a long period of intermediate forms

© 2008 Paul Billiet ODWS

ALLOPATRIC SPECIATION Geographical or reproductive isolation of

a part of the population would allow it to evolve in a different direction

Possibly more rapidly than the main population

If the isolated population is small, it might be very difficult to find fossils of the intermediate stages

© 2008 Paul Billiet ODWS

Species W

Species X

Species Y

Species Z Species YAllopatric speciation of Species W into species X due to the isolation of a small population of Species W

Allopatric speciation of species Y into species Z due to the isolation of a small population of species Y

Phyletic transition of species W into Species Y due to the slow gradual accumulation of mutations in Species W

Evolution

Tim

e

© 2008 Paul Billiet ODWS

THE PUNCTUATED EQUILIBRIUM MODEL They observed that the

fossil record gives a different picture for the evolution

They claim that there were long periods of stasis (4-10 million years) involving little evolutionary change

Then occasional rapid formation of new species

As little as 5,000 - 50,000 years

Stephen J Gould

Niles Eldredge

© 2008 Paul Billiet ODWS

Evolution

Tim

e Rapid speciation

Rapid speciation

Rapid speciation

Stasis

Stasis

Stasis

Species W

Species X

Species Y Species Z

© 2008 Paul Billiet ODWS

Problems...• Fossil evidence is the only Fossil evidence is the only

evidence of either theoryevidence of either theory• Not all characteristics of a species Not all characteristics of a species

are present in fossil recordare present in fossil record• Not necessarily proof of phylogenyNot necessarily proof of phylogeny

NATURAL SELECTION AT THE LEVEL OF THE ALLELE

Biston betulariaSickle cell anemia

D.2.10D.2.10 Describe one example of transient Describe one example of transient polymorphism.polymorphism.

• Polymorphisms = many “shapes” Polymorphisms = many “shapes” (phenotypes)(phenotypes)

• Industrial melanism: peppered mothIndustrial melanism: peppered moth– Biston betulariaBiston betularia– Peppered (grey)Peppered (grey)– Melanic (black)Melanic (black)– Pre-Industrial Revolution: advantageous to Pre-Industrial Revolution: advantageous to

be grey, camouflaged on tree barkbe grey, camouflaged on tree bark– Ind. Rev. Ind. Rev. soot on trees, black bark; black soot on trees, black bark; black

p’types survived (more fit)p’types survived (more fit)– Natural selection!Natural selection!– Clean Air Act…grey more fitClean Air Act…grey more fit– Temporary change Temporary change TRANSIENT TRANSIENT

polymorphismpolymorphism

D.2.11D.2.11 Describe sickle-cell anemia (SCA) as an Describe sickle-cell anemia (SCA) as an example of balanced polymorphism.example of balanced polymorphism.Xref- SCA-4.1.4; malariaXref- SCA-4.1.4; malaria

• 2/more alleles of population are not transient and changing. They’re stabilized by natural selection.

• Sickle-cell anemia – Balanced polymorphism – Heterozygotes have advantage in malarial

regions • HbAHbS

• More fit than either homozygote• AA = very susceptible to malaria• SS = sickle cell, but resistant to malaria• AS = some sickled cells, but usually not anemic;

K-deficient sickled cells kills Plasmodium parasite

– “S” Selected for & selected against ... balanced