Speciation

1. In your blog: What is a species?

D2.3 What is a species?

• Ecological species = set of organisms adapted to a particular set of resources in an environment (niche)

• Genetic species = similarity of DNA

• Evolutionary species = share a similar ancestor

• Breeding species = two organisms that are able to reproduce and produce fertile offspring

D2.3 What is a species? • Lions and tigers• Evolutionarily separated from

one another 3.7 million years ago

• Can interbreed– Ligers (Male lion, female tiger

cross) – Tiglons (Male tiger, female lion

cross) • But do not interbreed in the

wild– Lions are grassland cooperative

hunters– Tigers are woodland individual

hunters

• What about two populations which could potentially interbreed but do not because they are living in different niches or are separated by long distance?

• What about species that do not interbreed because they reproduce asexually? (bacteria or clonal plants)

D2.3 What is a species?

= mechanism by which organisms that are better adapted to the environment

survive and reproduce

Selection pressures (e.g. competition, predation, climatic factors, disease) keep

the numbers of “unselected” low

The “selected” reproduce more than the “unselected” and pass on their genes to the next generation.

Frequency of alleles which provide advantageous traits will increase over time.

Overproduction Heritable variationNatural selection

Inheritance

D2.4 Barriers between gene pools (reproductive isolating mechanisms)

1. Temporal isolationIncompatible time frames which prevent populations from encountering one another

Pinus radiata and Pinus attenuata do not hybridize because they have different pollination times

2. Geographical isolationPhysical barriers (land/water) prevent males and females from finding one anotherE.g. tree snails in Hawaii – one populations lives on one side of volcano, another on another side

D2.4 Barriers between gene pools (reproductive isolating mechanisms)

3. Behavioral isolationOne population’s lifestyle and habits are not compatible with another population

Birds rely on courtship display – different courtship displays not seductive enough

D2.4 Barriers between gene pools (reproductive isolating mechanisms)

D2 Speciation1. Feedback distributer: Estefania

2. Announcement: Final exam, Wednesday lunch

Liger fertilityBoth male ligers and male tigons are almost invariable sterile. The females of both species, however, are capable of breeding with either lions or tigers.

This will lead to further combinations of hybrid offspring, each of which has its own specific portmanteau name: Li-Ligers: The offspring of a female liger and a male lion (75% lion / 25% tiger). Ti-Ligers: The offspring of a female liger and a male tiger (75% tiger / 25% lion).Li-Tigons: The offspring of a female tigon and a male lion (75% lion / 25% tiger).Ti-Tigons: The offspring of a female tigon and a male tiger. (75% tiger / 25% lion).

D2.4 Polyploidy

• Haploid = one set of chromosomes (n)

• Diploid = two sets of chromosomes (2n)

• Polyploidy = cell which contains three or more sets of chromosomes (triploid (3n), tetraploid (4n), pentaploid (5n))

• Having extra set of chromosomes has consequence of making errors in replication more common

• Non-disjunction: cell with extra chromosome

• New species evolve from old species

D2.4 Polyploidy

D2.6 Types of speciation

• Allopatric speciation = species subject to geographical isolation

• Sympatric speciation =

new species formation while living in same geographical area– Temporal/Behavioral

Isolation

Evolution’s trick

D2.7,D2.8 Divergent Evolution• Divergent evolution = two or more

related species become dissimilar over time

• Adaptive radiation = similar but distinct species evolve from single species

• Darwin’s finches – Originate from population of ancestral

species that flew over from the mainland– Geographical isolation causes finches to

adapt to specific environments– Beaks well suited to type of food

available on the island

D2.8 Divergent Evolution• Gives rise to homologous structures = various

structures sharing the same fundamental plan

D2.8 Convergent Evolution• Convergent evolution = unrelated

species become similar in appearance as they adapt to the same kind of environment

• E.g. Marsupials in Australia and placental in North America– Marsupial: begin life in uterus but

move into pouch– Placentals: placenta connects growing

embryo within uterus to mother’s circulatory system

– Resemblance: overall shape, locomotion, feeding and foraging

• Marsupials in Australia and placentals in North America– Joined together as

Gondwana 200 mya– Australia split up and

species evolve independently

D2.8 Convergent Evolution

D2.8 Compare convergent and divergent evolution

• Gives rise to analogous structures = structures in different species having the same appearance, structure or function but have evolved separately

• E.g. Bat, bird, insect wings

D2 Punctuated equlibrium vs. gradualism

1. In your blog: What is the difference between convergent and divergent evolution?

2. Have your ring species homework out3. Feedback: Estefania

Ring species – speciation in action

• Adjacent populations of the salamander look similar and mate with one another

• Where the two ends of the loop overlap in Southern California, the two populations look quite different and behave as distinct species

D2.9 How fast does evolution occur?

Gradualism Punctuated equilibrium

Adopted by Charles Darwin (influenced by Charles Lyell)

Adopted in late 20th century (Stephen Jay Gould)

Evolution proceeds slowly by accumulation of small changes

Species do not change for a long period of time. Evolution occurs rapidly when there is an environmental change (e.g. volcanic eruption, meteorite impact)

To do

1. ‘A peek at the past’ activity

2. Read ‘Evolution in the Fast lane’ (on the web)

Punctuated eq• Arguments: We do not see

rapid evolution happening today in nature

• But evidence of evolution “in the fast lane”– Michael Bell, Stony Brook

University, NY– Loberg lake in Alaska – 1982 – sticklebacks

exterminated– Marine sticklebacks

recolonize lake, and evolve into freshwater sticklebacks (with no armor plate)

– Takes less than 20 years!

D2.11 Sickle cell anemia as an example of balanced polymorphism

• Polymorphism = two alleles in a gene pool

• Sickle cell anemia = Single base mutation in gene that codes for hemoglobin (Glutamic acid Valine)

• Episodes of pain. – chest, abdomen, joints as sickle cells block blood flow

• Normal (HbA), Sickle cell (HbS) allele• Heterozygous: has sickle-cell trait but resistant to

malaria

D2.11 Sickle cell anemia as an example of balanced polymorphism

• Greater frequency of HbS alleles in areas where malaria occur

D2.11 Sickle cell anemia as an example of balanced polymorphism