The Origin of Species Crash Course Video:

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: _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.

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 MAP AREA CANADA ALASKA Beaufort Sea Porcupine herd range NORTHWEST TERRITORIES Fairbanks Fortymile herd range Whitehorse ALASKA YUKON

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.

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

LE 24-6 A. harrisi A. leucurus Allopatric Speciation – Geographic Isolation

Geographic isolation of 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.

Geographic isolation of Darwin's Finches – Geographic Isolation Some birds from species A cross to a second island. The two populations no longer share a gene pool.

Geographic isolation of 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.

Geographic isolation of 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/ geographic isolation Videos 4/ htmlhttp://bcs.whfreeman.com/thelifewire/content/chp2 4/ html _structure/ev/m3/s2/evm3s2_4.htmhttp:// _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.

ALLOPATRIC vs. SYMPATRIC Allopatric speciation Sympatric speciation

Allopatric vs. Sympatric

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

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 = 6 4n = 12 4n4n 2n2n

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

Species B 2n = 6 Species A 2n = 4 Normal gamete n = 3 Normal gamete n = 3 2n = 10 Unreduced gamete with 4 chromosomes Unreduced gamete with 7 chromosomes Hybrid with 7 chromosomes Viable fertile hybrid (allopolyploid) Meiotic error; chromosome number not reduced from 2n 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.

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

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.

Explain Punctuated equilibrium Periods of stability, followed by periods of sudden major change and thus rapid speciation; The equilibrium happens during these periods of stability when organisms become well-adapted to environment; Natural selection acts to maintain characteristics during the equilibrium; This equilibrium punctuated by rapid environmental change, such as volcanic eruption / meteor impact / change in sea level; If a change in the environment creates a selective pressure that strongly selects for a particular phenotype then this directional selection will lead to rapid evolution; Evidence for punctuated equilibrium is in the fossil record where missing links/ intermediate species have not been found between groups of species

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 Time Gradualism model Punctuated equilibrium model