2. AP Biology 2007-2008 Mom, Dad… There’s something you need to know… I’m a MAMMAL! The Origin of Species

3. AP Biology So…what is a species?  Biological species concept  defined by Ernst Mayr  population whose members can interbreed & produce viable, fertile offspring  reproductively compatible Western MeadowlarkEastern Meadowlark Distinct species: songs & behaviors are different enough to prevent interbreeding

4. AP Biology How and why do new species originate?  Species are created by a series of evolutionary processes  populations become isolated  geographically isolated  reproductively isolated  isolated populations evolve independently  Isolation  allopatric  geographic separation  sympatric  still live in same area

5. AP Biology  Obstacle to mating or to fertilization if mating occurs Pre-reproduction barriers behavioral isolation geographic isolation ecological isolation temporal isolation mechanical isolation gametic isolation

6. AP Biology Geographic isolation  Species occur in different areas  physical barrier  allopatric speciation  “other country” Harris’s antelope squirrel inhabits the canyon’s south rim (L). Just a few miles away on the north rim (R) lives the closely related white-tailed antelope squirrel Ammospermophilus spp

7. AP Biology Ecological isolation  Species occur in same area, but occupy different habitats so rarely encounter each other 2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial lions & tigers could hybridize, but they live in different habitats:  lions in grasslands  tigers in rainforest lions & tigers could hybridize, but they live in different habitats:  lions in grasslands  tigers in rainforest

8. AP Biology Temporal isolation  Species that breed during different times of day, different seasons, or different years cannot mix gametes  sympatric speciation  “same country” Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

9. AP Biology Behavioral isolation  Unique behavioral patterns & rituals isolate species  identifies members of species  attract mates of same species  courtship rituals, mating calls Blue footed boobies mate only after a courtship display unique to their species sympatric speciation?

10. AP Biology Mechanical isolation  Morphological differences can prevent successful mating Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. These 2 species of monkey flower differ greatly in shape & color, therefore cross-pollination does not happen. Plants sympatric speciation?

11. AP Biology Mechanical isolation  For many insects, male & female sex organs of closely related species do not fit together, preventing sperm transfer  lack of “fit” between sexual organs: hard to imagine for us… but a big issue for insects with different shaped genitals! Animals I can’t even imagine!

12. AP Biology Gametic isolation  Sperm of one species may not be able to fertilize eggs of another species  mechanisms  biochemical barrier so sperm cannot penetrate egg  receptor recognition: lock & key between egg & sperm  chemical incompatibility  sperm cannot survive in female reproductive tract Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse. sympatric speciation?

13. AP Biology Post-reproduction barriers  Prevent hybrid offspring from developing into a viable, fertile adult  reduced hybrid viability  reduced hybrid fertility  hybrid breakdown zebroid

14. AP Biology Reduced hybrid viability  Genes of different parent species may interact & impair the hybrid’s development Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail. sympatric speciation?

15. AP Biology Mules are vigorous, but sterile Reduced hybrid fertility  Even if hybrids are vigorous they may be sterile  chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes Donkeys have 62 chromosomes (31 pairs) Horses have 64 chromosomes (32 pairs) Mules have 63 chromosomes!

16. AP Biology Hybrid breakdown  Hybrids may be fertile & viable in first generation, but when they mate offspring are feeble or sterile In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. On path to separate species. In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. On path to separate species. sympatric speciation?

17. AP Biology Niles Eldredge Curator American Museum of Natural History Rate of Speciation  Current debate: Does speciation happen gradually or rapidly  Gradualism  Charles Darwin  Charles Lyell  Punctuated equilibrium  Stephen Jay Gould  Niles Eldredge

18. AP Biology Gradualism  Gradual divergence over long spans of time  assume that big changes occur as the accumulation of many small ones

19. AP Biology Punctuated Equilibrium  Rate of speciation is not constant  rapid bursts of change  long periods of little or no change  species undergo rapid change when they 1 st bud from parent population Time

20. AP Biology 2007-2008 Any Questions??

21. AP Biology Fitness  Survival & Reproductive success  individuals with one phenotype leave more surviving offspring Body size & egg laying in water striders

22. AP Biology Variation & natural selection  Variation is the raw material for natural selection  there have to be differences within population  some individuals must be more fit than others

23. AP Biology Mean beak depth of parents (mm) Medium ground finch 8 891011 9 10 11 1977198019821984 Dry year Wet year Beak depth Beak depth of offspring (mm) Where does Variation come from?  Mutation  random changes to DNA  errors in mitosis & meiosis  environmental damage  Sex  mixing of alleles  recombination of alleles  new arrangements in every offspring  new combinations = new phenotypes  spreads variation  offspring inherit traits from parent

24. AP Biology 5 Agents of evolutionary change MutationGene Flow Genetic DriftSelection Non-random mating

25. AP Biology 1. Mutation & Variation  Mutation creates variation  new mutations are constantly appearing  Mutation changes DNA sequence  changes amino acid sequence?  changes protein?  changes structure?  changes function?  changes in protein may change phenotype & therefore change fitness

26. AP Biology 2. Gene Flow  Movement of individuals & alleles in & out of populations  seed & pollen distribution by wind & insect  migration of animals  sub-populations may have different allele frequencies  causes genetic mixing across regions  reduce differences between populations

27. AP Biology 3. Non-random mating  Sexual selection

28. AP Biology Warbler finch Tree finches Ground finches 4. Genetic drift  Effect of chance events  founder effect  small group splinters off & starts a new colony  bottleneck  some factor (disaster) reduces population to small number & then population recovers & expands again

29. AP Biology Founder effect  When a new population is started by only a few individuals  some rare alleles may be at high frequency; others may be missing  skew the gene pool of new population  human populations that started from small group of colonists  example: colonization of New World

30. AP Biology Bottleneck effect  When large population is drastically reduced by a disaster  famine, natural disaster, loss of habitat…  loss of variation by chance event  alleles lost from gene pool  not due to fitness  narrows the gene pool

31. AP Biology Cheetahs  All cheetahs share a small number of alleles  less than 1% diversity  as if all cheetahs are identical twins  2 bottlenecks  10,000 years ago  Ice Age  last 100 years  poaching & loss of habitat

32. AP Biology Conservation issues  Bottlenecking is an important concept in conservation biology of endangered species  loss of alleles from gene pool  reduces variation  reduces adaptability Breeding programs must consciously outcross Peregrine Falcon Golden Lion Tamarin

33. AP Biology 5. Natural selection  Differential survival & reproduction due to changing environmental conditions  climate change  food source availability  predators, parasites, diseases  toxins  combinations of alleles that provide “fitness” increase in the population  adaptive evolutionary change

34. AP Biology 5 Agents of evolutionary change MutationGene Flow Genetic DriftSelection Non-random mating

35. AP Biology

36. Hardy-Weinberg Theorem genetic structure of a non-evolving population remains constant + sexual recombination cannot alter the relative frequencies of alleles - Hardy-Weinberg equilibrium Hardy-Weinberg equation p 2 + 2pq + q 2 = 1 p 2 : frequency of AA genotype 2pq: frequency of Aa genotype q 2 : frequency of aa genotype - p: frequency of A allele - q: frequency of a allele

37. AP Biology Hardy-Weinberg  HW law states --> original of a genotypes alleles remains CONSTANT  HW Equilibrium... is defined algebraically any gene with 2 allelic forms... A and a  let frequency of one allele (A) = p & frequency of other allele (a) = q  then by definition, p + q = 1  HW equation... (p + q)2 = p2 + 2 pq + q2 = 1  AA Aa aa

38. AP Biology