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Ch 24 – Origin of Species

Ch 24 – Origin of Species. pt 1. Speciation , the origin of new species How do new species originate and how populations evolve? Microevolution - changes in allele frequency in a population over time Macroevolution - broad patterns of evolutionary change above the species level.

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Ch 24 – Origin of Species

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  1. Ch 24 – Origin of Species pt 1

  2. Speciation, the origin of new species • How do new species originate and how populations evolve? • Microevolution- changes in allele frequency in a population over time • Macroevolution - broad patterns of evolutionary change above the species level

  3. The Biological Species Concept • A speciesis a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations • Gene flow between populations holds the phenotype of a population together

  4. Reproductive Isolation • Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring • Hybridsare the offspring of crosses between different species • Reproductive isolation can be classified by whether factors act before or after fertilization

  5. Prezygotic barriers • Prezygotic barriers block fertilization from occurring by: • Impeding different species from attempting to mate • Preventing the successful completion of mating • Hindering fertilization if mating is successful

  6. Prezygotic barriers Gametic Isolation Mechanical Isolation Habitat Isolation Temporal Isolation Behavioral Isolation MATING ATTEMPT FERTILIZATION (g) (c) (e) (f) Snails (d) Blue-footed booby Sea urchin Spotted skunk Garter snakes

  7. Mating dance – superb bird of paradise: • http://www.youtube.com/watch?v=7dx2CUMtZ-0 • Blue footed booby mating dance • http://www.youtube.com/watch?v=1NAKg46s1DA

  8. Postzygotic barriers • Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult: • Reduced hybrid viability • Reduced hybrid fertility • Hybrid breakdown

  9. Postzygotic barriers Hybrid Breakdown Reduced Hybrid Fertility Reduced Hybrid Viability VIABLE, FERTILE OFFSPRING FERTILIZATION (i) (h) (l) salamanders (j) Cultivated rice (k) Mule

  10. Limitations of the Biological Species Concept • The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes) • The biological species concept emphasizes absence of gene flow • However, gene flow can occur between distinct species • For example, grizzly bears and polar bears can mate to produce “grolarbears” • Other species concepts: ecological, morphological

  11. Speciation can take place with or without geographic separation • Speciation can occur in two ways: • Allopatric speciation • Sympatric speciation

  12. (a) Allopatric speciation. A population forms a new species while geographically isolated from its parent population. Sympatric speciation. A subset of a population forms a new species without geographic separation. (b)

  13. Process of Allopatric Speciation A. harrisii A. leucurus • The definition of barrier depends on the ability of a population to disperse • For example, a canyon may create a barrier for small rodents, but not birds, coyotes, or pollen Allopatric speciation of antelope squirrels on opposite rims of the Grand Canyon.

  14. Separate populations may evolve independently through mutation, natural selection, and genetic drift • Reproductive isolation may arise as a result of genetic divergence • For example, mosquitofish in the Bahamas comprise several isolated populations in different ponds (a) Under high predation (b) Under low predation

  15. Evidence of Allopatric Speciation • 15 pairs of sibling species of snapping shrimp (Alpheus) are separated by the Isthmus of Panama • These species originated 9 to 13 million years ago, when the Isthmus of Panama formed and separated the Atlantic and Pacific waters

  16. Atlantic Ocean Isthmus of Panama Pacific Ocean

  17. A. formosus

  18. A. panamensis

  19. A. nuttingi

  20. A. millsae

  21. Trends • More geographic barriers tends to lead to more species • Reproductive isolation between species increases as distance between them increases

  22. Evolution videos: • Salamander speciation • http://www.youtube.com/watch?v=YCoEiLOV8jc

  23. Sympatric (“Same Country”)Speciation • In sympatric speciation, speciation takes place in geographically overlapping populations

  24. Polyploidy speciation • Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division • Polyploidy is much more common in plants than in animals. Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids • An autopolyploid is an individual with more than two chromosome sets, derived from one species • An allopolyploid is a species with multiple sets of chromosomes derived from different species

  25. Habitat differentiation • Sympatric speciation can also result from the appearance of new ecological niches • For example, the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees

  26. Sexual Selection EXPERIMENT Monochromatic orange light Normal light • Sexual selection can drive sympatric speciation • Sexual selection for mates of different colors has likely contributed to speciation in cichlid fish in Lake Victoria P. pundamilia P. nyererei

  27. Hybrid zones EUROPE • 2 different species mate and produce hybrids, 2 species have incomplete reproductive barriers Fire-bellied toad range Fire-bellied toad, Bombina bombina Hybrid zone Yellow-bellied toad range 0.99 Hybrid zone 0.9 Frequency of B. variegata-specific allele Yellow-bellied toad range Fire-bellied toad range 0.5 Yellow-bellied toad, Bombina variegata 0.1 0.01 10 0 20 10 20 30 40 Distance from hybrid zone center (km)

  28. When closely related species meet in a hybrid zone, there are three possible outcomes: • Reinforcement, Fusion, Stability Possible outcomes: Isolated population diverges Hybrid zone Reinforcement OR Fusion OR Gene flow Hybrid individual Population Barrier to gene flow Stability

  29. Speciation over time • The fossil record includes examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear • Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibria 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

  30. (a) Punctuated pattern Time (b) Gradual pattern

  31. Rate of speciation • The punctuated pattern in the fossil record and evidence from lab studies suggest that speciation can be rapid • The interval between speciation events can range from 4,000 years (some cichlids) to 40 million years (some beetles), with an average of 6.5 million years

  32. Evo– devo videos • Eye evolution • http://www.pbs.org/wgbh/evolution/library/01/1/quicktime/l_011_01.html • Homeobox genes • http://www.pbs.org/wgbh/evolution/library/03/4/l_034_04.html

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