Introductory Questions #1 (fifth overall)

1. Introductory Questions #1 (fifth overall) • How would you define a species? What are two key factors you must consider? • What is the key as to how a new species forms? • Explain the difference between a prezygotic barrier and a postzygotic barrier. • How is allopatric speciation different from sympatric speciation? • Name the two models that have been proposed to explain evolution observed in the fossil record.

2. Introductory Questions #2 • Give two examples of a prezygotic and postzygotic barrier. • Why is sympatric speciation more common in plants vs. animals? • Which model (gradualism or puntuated equilibrium) is more reflective of the fossil record? Briefly explain why? • How do new body designs and evolutionary novelties form? • What is allometric growth and paedomorphosis? • When was the last mass extinction event? How many have occurred in the last 600 million years?

3. Macroevolution & Speciation Chapter 24 • Define a Species • Isolation • Extinction Events • Geological Timetable • Phylogenetics

4. Overview of the Existence of Species • Estimated number of 13-14 million different species • Only 1.75 million have been scientifically named • The breakdown: -250,000 Plants -42,000 Vertebrates -750,000 Insects How would you define a species?

5. What is a species? • Biological species concept (Mayr):a population or group of populations whose members have the • potential to interbreed • produce viable, fertile offspring (genetic exchange is possible and that is genetically isolated from other populations)

6. What is a Species? • Considered separate species if they cannot interbreed (or are reproductively isolated)

7. How Does a new Species Emerge? • There has to be some ISOLATION event that separates a population of individuals • Separation has to be maintained with barriers • Applies to sexually reproducing organisms • Asexual reproducers: species concept is difficult to apply -classified by structural & biochemical differences

8. Modes of Reproductive Isolation

9. Prezygotic Barriers • Prezygotic barriers:impede mating between species or hinder the fertilization of the ova • Habitat (snakes; water/terrestrial) • Behavioral (fireflies; mate signaling & courtship) • Temporal (salmon; seasonal mating) • Mechanical (flowers; pollination anatomy) • Gametic (frogs; egg coat receptors)

10. Postzygotic Barriers Postzygotic Barriers: fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adult Reduced hybrid viability frogs; zygotes fail to develop or reach sexual maturity Reduced hybrid fertility mule; horse x donkey; cannot backbreed Hybrid breakdown cotton; 2nd generation hybrids are sterile

11. What if they breed, but don’t produce viable offspring?(mules)

12. Problem With “Species” Definition: If they never have the opportunity to interbreed, how do you know if they can?

13. We Can Separate Species Based On % Of Shared Dna How Much of a difference is needed to call 2 organisms separate species?

14. Modes of speciation (based on how gene flow is interrupted) Allopatric:populations segregated by a geographical barrier; can result in adaptive radiation (island species) Sympatric:reproductively isolated subpopulation in the midst of its parent population (change in genome); -polyploidy in plants -cichlid fishes

15. Punctuated Equilibrium • Tempo of speciation: gradual vs. divergence in rapid bursts; Niles Eldredge and Stephen Jay Gould (1972); helped explain the non-gradual appearance of species in the fossil record

16. The fossil of the earliest known bird, Archeaopteryx, was discovered in 1861 • Fossils of dinosaurs with feathers may support the bird-dinosaur theory

17. Small genetic changes in a population • Change in frequency of a single allele due to selection Microevolution

18. Macroevolution • Large-scale changes in organisms • Involves new genera

19. Macroevolution • Macroevolution consists of the major changes in the history of life • The fossil record chronicles these changes, which have helped to devise the geologic time scale

20. Macroevolution: the origin of new taxonomic groups • Speciation: the origin of new species • 1- Anagenesis (phyletic evolution): accumulation of heritable changes • 2- Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity)

21. Adaptive Radiation

22. Example: Galápagos • But volcanic activity can also destroy life • Example: Krakatau • By forming new islands, volcanoes can create opportunities for organisms Figure 15.4B, C

23. Extinction • The elimination a species from the earth • Background Extinction Rate - relatively constant rate of extinction in the fossil record • Mass Extinction - major loss of species: climate change, humans, catastrophies

24. ? Cretaceousextinctions 90 million years ago 80 70 65 60 Figure 15.5

26. Mass Extinctions - These mass extinctions may have been a result of an asteroid impact or volcanic activity • Every mass extinction reduced the diversity of life • But each was followed by a rebound in diversity Ex. Mammals filled the void left by the dinosaurs Six Mass Extinction Events in the last 600 million years (2) of the major extinctions are: -Permian (90% of all marine species went extinct) -Cretaceous (Killed the dinosaurs)

27. Figure 15.1

28. Every mass extinction reduced the diversity of life

29. CRITICAL QUESTION:How Do Humans Affect Extinction Rates?

30. How Do Humans Affect Extinction Rates? • Simplify ecosystems • (monocultures/disturbed habitats) • Strengthen pest populations • Eliminate predators (can create new pests)

31. How Do Humans Affect Extinction Rates? • Introduce new species (starlings) • Overharvest • Interfer with chemical cycling and energy flow (UV/ozone, heat pollution)

32. Are Birds Really Dinosaurs with Feathers? • Did birds evolve from dinosaurs? • Evolutionary biologists investigate this question by looking at the fossil record

33. The actual ages of rocks and fossils mark geologic time • The sequence of fossils in rock strata indicates the relative ages of different species • Radiometric dating can gauge the actual ages of fossils

34. Continental drift has played a major role in macroevolution • Continental drift is the slow, incessant movement of Earth’s crustal plates on the hot mantle EurasianPlate NorthAmericanPlate AfricanPlate PacificPlate Splitdeveloping NazcaPlate SouthAmericanPlate Indo-AustralianPlate Antarctic Plate Edge of one plate being pushed over edge of neighboring plate (zones of violent geologic events) Figure 15.3A

35. CENOZOIC • This movement has influenced the distribution of organisms and greatly affected the history of life Eurasia North America Africa India SouthAmerica Australia • Continental mergers triggered extinctions • Separation of continents caused the isolation and diversification of organisms • Rate : 1-2 cm/year Antarctica Laurasia Millions of years ago MESOZOIC Gondwana Pangaea PALEOZOIC Figure 15.3B

36. Continental Drift/Plate Tectonics Pangea (Paleozoic)  Laurasia Gondwana (Mesozoic)   • Europe -S. America • Greeland -Australia • N. America -Africa (Cenozoic) **First Proposed by Alfred Wegner (1912) **Later Reproposed in the 1960’s after WWII and sonar mapping of the ocean floor

38. Lungfishes evolved when Pangaea was intact • Continental drift explains the distribution of lungfishes Figure 15.3C

39. NORTHAMERICA ASIA EUROPE AFRICA SOUTHAMERICA AUSTRALIA = Living lungfishes = Fossilized lungfishes Figure 15.3D

40. Connection: Tectonic trauma imperils local life • Plate tectonics, the movements of Earth’s crustal plates, are also associated with volcanoes and earthquakes • California’s San Andreas fault is a boundarybetween two crustal plates San Andreas fault San Francisco Santa Cruz Los Angeles Figure 15.4A