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Speciation

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

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Speciation

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  1. Speciation 1. In your blog: What is a species?

  2. 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

  3. 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

  4. D2.3 What is a species? • 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)

  5. Overproduction Heritable variation Natural selection = 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 Inheritance 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.

  6. D2.4 Barriers between gene pools (reproductive isolating mechanisms) • Temporal isolation Incompatible time frames which prevent populations from encountering one another Pinusradiataand Pinusattenuata do not hybridize because they have different pollination times

  7. D2.4 Barriers between gene pools (reproductive isolating mechanisms) 2. Geographical isolation Physical barriers (land/water) prevent males and females from finding one another E.g. tree snails in Hawaii – one populations lives on one side of volcano, another on another side

  8. D2.4 Barriers between gene pools (reproductive isolating mechanisms) 3. Behavioral isolation One population’s lifestyle and habits are not compatible with another population Birds rely on courtship display – different courtship displays not seductive enough

  9. D2 Speciation Feedback distributer: Estefania Announcement: Final exam, Wednesday lunch

  10. Liger fertility Both 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).

  11. 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))

  12. D2.4 Polyploidy • 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

  13. D2.6 Types of speciation • Allopatricspeciation = species subject to geographical isolation • Sympatricspeciation= new species formation while living in same geographical area • Temporal/Behavioral Isolation

  14. Evolution’s trick

  15. 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

  16. D2.8 Divergent Evolution • Gives rise to homologous structures = various structures sharing the same fundamental plan

  17. D2.8 Convergent Evolution • Convergent evolution = unrelated species become similarin 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

  18. D2.8 Convergent Evolution • Marsupials in Australia and placentals in North America • Joined together as Gondwana 200 mya • Australia split up and species evolve independently

  19. 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

  20. D2 Punctuated equlibrium vs. gradualism In your blog: What is the difference between convergent and divergent evolution? Have your ring species homework out Feedback: Estefania

  21. 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

  22. D2.9 How fast does evolution occur?

  23. To do • ‘A peek at the past’ activity 2. Read ‘Evolution in the Fast lane’ (on the web)

  24. 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!

  25. 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

  26. D2.11 Sickle cell anemia as an example of balanced polymorphism • Normal (HbA), Sickle cell (HbS) allele • Heterozygous: has sickle-cell trait but resistant to malaria

  27. D2.11 Sickle cell anemia as an example of balanced polymorphism • Greater frequency of HbS alleles in areas where malaria occur

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