The Origin of SpeciesCrash Course Video:

https://www.youtube.com/watch?v=2oKlKmrbLoU

IB LEARING OBJECTIVE

• Discuss the definition of the term species.

• Species is a Latin word meaning “kind” or “appearance”

• Video Explain what is a species:

http://www.blackwellpublishing.com/ridley/video_gallery/

DD_What_is_a_species.asp

Definition of species

• A group of organisms that:

– have a common ancestry

– closely resemble each other both structurally and biochemically

– are members of a natural population that are actually or potentially capable of breeding with each other to produce fertile offspring

– Do not interbreed with members of other species.

IB LEARING OBJECTIVE

• Discuss the definition of the term species.

LE 24-3

Similarity between different species.

Diversity within a species.

IB LEARNING OBJECTIVE

• Define allele frequency and gene pool.

Gene Pools and Allele Frequencies

• A population is a localized group of individuals capable of interbreeding and producing fertile offspring

• The gene pool is the total genes and their different alleles in a population at any one time

LE 23-3

MAPAREA

CA

NA

DA

AL

AS

KA

Beaufort Sea

Porcupineherd range NO

RTH

WEST

TERR

ITOR

IES

Fairbanks

Fortymileherd range

Whitehorse

AL

AS

KA

YU

KO

N

• Allele frequency is the commonness of the occurrence of any particular allele in a population (example: commonness of green eyes).

• If allele frequency of a population are changing –then evolution is occurring within the population

• If allele frequency is staying the same – then the population in not evolving.

IB LEARNING OBJECTIVE

Describe three examples of barriers between gene pools. Examples include

– geographical isolation,

– hybrid infertility,

– temporal isolation

– and behavioural isolation.

IB LEARNING OBJECTIVE

• Explain how polyploidy can contribute to speciation.

Polyploidy

• Polyploidy is presence of extra sets of chromosomes due to accidents during cell division

• It has caused the evolution of some plant species

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

LE 24-8

Failure of cell division in a cell of a growing diploid plant after chromosome duplication gives rise to a tetraploid branch or other tissue.

Gametes produced by flowers on this tetraploid branch are diploid.

Offspring with tetraploid karyo-types may be viable and fertile—a new biological species.

2n = 64n = 12 4n

2n

Speciation by Polyploidy – form of mutation

• Types of polyploid

– Autopolyploidy – if the additional chromosome set comes from the same species

– Allopolyploidy -- if the additional chromosome set comes from a different species…. Forming a new species

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Species B2n = 6

Species A2n = 4

Normal gameten = 3

Normal gameten = 3

2n = 10

Unreduced gametewith 4 chromosomes

Unreduced gametewith 7 chromosomes

Hybrid with7 chromosomes

Viable fertile hybrid(allopolyploid)

Meiotic error;chromosomenumber notreduced from2n to n

Examples of polyploidy

Causes of Polyploidy – form of mutation

• Mutation – random change in genetic information

• Chromosomal Mutation – change in chromosome structure or number of chromosomes

• Polyploid – is a chromosomal mutation in which an organism has more than two sets of chromosomes.

Causes of Polyploidy – form of mutation

• Mutation – random change in genetic information

• Chromosomal Mutation – change in chromosome structure or number of chromosomes

• Polyploid – is a chromosomal mutation in which an organism has more than two sets of chromosomes.

IB LEARNING OBJECTIVE

• Compare allopatric and sympatric speciation.

– Speciation: the formation of a new species by splitting of an existing species.

– Sympatric: in the same geographical area.

– Allopatric: in different geographical areas.

Process of Speciation – the evolution of a new species

• Speciation may occur when a population becomes permanently isolated from the main bulk of the population.

• Thus two populations become reproductively isolated from each other.

• There are two types

– Allopatric speciation

– Sympatirc Speciation

Process of Speciation – the evolution of a new species

• Allopatric speciation occurs when members of a groups migrate to a new area, and form a new population that is geographically isolated from the rest of the population.

• We call the reproductive isolation, geographic isolation.

Geographic Isolation 

– Geographic Isolation 

• Geographic isolation occurs when two populations are separated by geographic barriers such as rivers , mountains or islands.

LE 24-5

Allopatric speciation Sympatric speciation

Allopatric Speciation

• Speciation in Darwin's Finches

– Speciation in the Galápagos finches occurred by:

• founding of a new population

• geographic isolation

• changes in new population's gene pool via genetic drift, natural selection and random mutation.

• reproductive isolation

Allopatric Speciation in Darwin's Finches

Founders Arrive 

A few finches—species A—travel from South America to one of the Galápagos Islands.

There, they survive and reproduce.

Allopatric Speciation in Darwin's Finches

– Geographic Isolation

Some birds from species A cross to a second island.

The two populations no longer share a gene pool.

Allopatric Speciation in Darwin's Finches

• Changes in the Gene Pool

Seed sizes on the second island favor birds with large beaks.

The population on the second island evolves into population B, with larger beaks.

Allopatric Speciation in Darwin's Finches

– Reproductive Isolation

• If population B birds cross back to the first island, they will not mate with birds from population A.

• Populations A and B are separate species.

Allopatric Speciation Videos

• http://bcs.whfreeman.com/thelifewire/content/chp24/2402002.html

• http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ev/m3/s2/evm3s2_4.htm

Sympatric Speciation

Sympatric Speciation occurs when two varieties of species live in the same geographical area, but do not interbreed.

This can happen via three isolation mechanisms:

1.Behavioural Isolation

2.Temporal Isolation

3.Hybrid Infertility

Sympatric Speciation via behavioral isolation.

Behavioural/ temporal Isolation EXAMPLE

–The apple maggot fly of North America use to lay its eggs only on hawthorn fruit, which is its food.

–Now it lays eggs on apples too

–One strain of this population lays its eggs on hawthorn fruit and the other lays it eggs on apples

–Because these fruit ripen at different times, adults emerge and mate at different times, so there is now a behavioral and temporal isolation between these two populations.

–And now there is also observable differences in these two populations allele frequency.

Sympatric speciation via hybrid infertility

• Reproductive Barriers can also occur through hybrid infertility.

• Hybrids occur by the fusion of diploid gametes (usually only in plants)

• Remember most gametes are haploid

– The fusion of diploid gametes forms tetraploid adults, and tetraploid adults can only mate and have fertile offspring with other tetraploid adults

– Organism with more than a diplod set of chromosomes are called polyploidy

ALLOPATRIC vs. SYMPATRIC

Allopatric speciation Sympatric speciation

LE 24-6

s

A. harrisi A. leucurus

Allopatric Speciation – Geographic Isolation

Allopatric vs. Sympatric

IB LEARNING OBJECTIVE

• Compare convergent and divergent evolution.

HOMOLOGOUS vs ANALOGOUS STURCTURES

• Homologous Structures – Have similar structure, but may have different function (divergent evolution)

• Analogous Structures – Have different structures but similar functions. (convergent evolution)

Homology

• Homology is similarity resulting from common ancestry. Example of Divergent Evolution.

Anatomical Homologies• The pendadactyl limb in

vertebrate animals is an example of divergent evolution.

• In the pendactly limb animals have similar bone structure b/c these vertebrates diverge from a common ancestor.

• But these vertebrates use these limbs for different forms of mobility

Divergent Evolution

• Divergent Evolution -- The process by which an interbreeding population or species diverges into two or more descendant species, resulting in once similar or related species to become more and more dissimilar.

• Example:Example:

Analogous Structures

• Analogous Structures are similar in function, differ in structure did NOT inherited from a COMMON ancestor

• For example, the wing of a bird and the wing of an insect are classified as being analogous structures since their structures are unrelated

• Evolved independently

• Example of convergent evolution

Convergent Evolution

• Convergent Evolution-- A kind of evolution wherein organisms evolve structures that have similar (analogous) structures or functions in spite of their evolutionary ancestors being very dissimilar or unrelated.

• Examples: the wings of bats, birds, and insects evolved independently from each other but all are independently from each other but all are used to perform the function of flying used to perform the function of flying

IB LEARNING OBJECTIVE

• Outline the process of adaptive radiation.

Adaptive Radiation

• Adaptive radiation is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities

• Many species evolving from one species is known as divergent evolution

Adaptive Radiation Example

• Adaptive Radiation Can happen in two situations:

– One groups has a competitive advantage over the other.

– There are opportunities that no other species is utilizing.

Adaptive Radiation Example

• Adaptive Radiation Can happen in two situations:

– One groups has a competitive advantage over the other.

• This happened on the Galapagos Islands when some finches within a population had a strong beak and could break open more different types of seeds. These strong beak population eventually became a different species, specializing in seeds with hard coats.

• Other finches specialized in other things (example: eating parasites off of lizards and tortoises, or sucking blood from mammals (vampire finches)) and became a different species.

Adaptive Radiation – Competitive Advantage

Adaptive Radiation Example

• Adaptive Radiation Can happen in two situations:

– There are opportunities that no other species is utilizing.

• This occurred with mammals after the dinosaurs went extinct (65mya)

• There were many opportunities that no living organisms were using. Thus many species of many mammals evolved during the time.

• Adaptive Radiation -- Opportunities

IB LEARNING OBJECTIVE

• Discuss ideas on the pace of evolution, including gradualism and punctuated equilibrium.

Pace of Evolution

• There are two scientific ideas about the rate of evolution:

– Gradualism

– Punctuated Equilibrium

Pace of Evolution: Gradualism vs. Punctuated Equilibria

• Gradualism – The observation that evolution by natural selection is an exceedingly gradual process…takes millions and millions of years.

Punctuated Equilibrium

• The fossil record includes many episodes in which new species appear suddenly in a geologic stratum, persist essentially unchanged through several strata, and then apparently disappear

• Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change

• The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence

Punctuated Equilibrium

• Hypothesis holds that:

– When environments become unfavorable, populations attempt to migrate to a more favorable situation

– If environmental condition are extremely violent a mass extinction can occur.

– Populations at the edge of extinction may survive

– These surviving populations may be small and may eventually re-populate

Punctuated Equilibrium

• Hypothesis holds that:

– The alleles of the surviving group may not reflect the original gene pool of the population

– Thus these new alleles frequency will be the basis for change in the new conditions in the environment.

LE 24-13

Time

Gradualism model Punctuated equilibrium model

IB LEARNING OBJECTIVES

• Describe one example of transient polymorphism.

– An example of transient polymorphism is industrial melanism.

•  

Polymorphorism

• A population in which there are two alleles of a gene in the pool is polymorphic.

• The are two types of polymorphism.

– Transient Polymorphism

– Balanced Polymorphism

Transient Polymorphism

• Transient Polymorphism is when one allele is gradually replacing the other.

An example is the Pepper Moth Biton betula.

This moth comes in two melanic forms (colors)

Both these forms are de to dominant alleles that affect wing colors.

Polymorphorism

• The pepper moth in England. It exists as a white moth and a black moth.

• Before the industrial revolution the white allele frequency was higher than the black.

• Then after the industrial revolution the black allele frequency was higher

Example #2: The Case of the Peppered Moth (Biston betularia)

Before 1848:

•Found near Manchester, England

•Trees where they rested were covered with off-white lichen.

•Moths were white, therefore camouflaged from the predation of birds-best adapted

•Occasionally a black moth would appear and thus would have a very high chance of being eaten by a bid before reproducing.

The Case of the Peppered Moth (Biston betularia)

After 1848:

•Coal-based industry covered trees with soot.

•White moths were easily spotted and eaten.

•The black moth now had the advantage and became predominant-best adapted. (95%)

The Case of the Peppered Moth (Biston betularia)

Now:

•Reduced use of coal has made trees green (covered in algae).

•Both forms of moth are commonthis is called “polymorphism”

IB LEARNING OBJECTIVE

• Describe sickle-cell anemia as an example of balanced polymorphism.

– Sickle-cell anemia is an example of balanced polymorphism where heterozygotes (sickle-cell trait) have an advantage in malarial regions because they are fitter than either homozygote.

Balanced Polymorphism• Balanced Polymorphism – is when two alleles of

a gene can persists indefinitely in the gene pool of a population.

• Example: Sickle Cell Anemia (review Sickle Cell Anemia Powerpoint or Page 23 in Green study guide OR pages 475 to 477 in Pink Textbook.)

– Individuals with HbA HbA (genotype)do not have sickle cell anemia but are susceptible to Malaria

– Individuals with HbS HbS (genotype) do have sickle cell anemia and resistant to Malaria

– Individuals with HbA HbS (genotype)do do not have sickle cell anemia and are resistant to Malaria

Balanced Polymorphism

The sickle cell allele is really prevalent in areas where there is high levels of Malaria (i.e. Africa)

As many as 40% of the African Population are carriers of sickle cell allele, so show resistance to malaria