How Populations Evolve

1. How Populations Evolve

2. Population Genetics • turning point for evolutionary theory • emphasizes extensive genetic variation within populations • recognizes importance of quantitative characters • reconciled Darwinism and Mendelism

3. neo-Darwinism • Integrates ideas from many different fields • paleontology • taxonomy • biogeography • population genetics • Architects of neo-Darwinism • Theodosius Dobzhansky • Ernst Mayr • George Gaylord Simpson • G. Ledyard Stebbins

4. POPULATIONS • a localized group of individuals belong to the same species

5. Adapted from: Lederer R.J. 1984. Ecology and field biology. Menlo Park, CA.: Benjamin/Cummings. P. 200. population population population population population population population community

6. Population Fluctuations (+) natality Population of organisms (-) emigration (+) immigration (-) mortality Adapted from: Lederer RJ. 1984. Ecology and field biology. Menlo Park, CA.: Benjamin/Cummiongs. P. 207

7. A large mammals Number of survivors B humans, fruitflies, hydras, birds tree seedlings Adapted from: Lederer R.J. 1984. Ecology and field biology. Menlo Park, CA.: Benjamin/Cummings. P. 210. C oysters, salmon most invertebrates Age

8. B = birth D = death Equilibrium phase Carrying capacity of environment B approx D Number of organisms Exponential Growth B>D Adapted from: Lederer R.J. 1984. Ecology and field biology. Menlo Park, CA.: Benjamin/Cummings. P. 211. Lag phase B approx D Time

9. Adapted from: Miller, Jr. GT. 1990. Living in the environment, 6th ed. Belmont, CA.: Wadsorth. P. 4. 16 Exponential Growth of World Population Billions of people 8 Black death (bubonic plague) 0 8000bc 7000bc 6000bc 5000bc 4000bc 3000bc 2000bc 1000bc 1ad 1000ad 2000ad 21000ad

10. SPECIES • a group of populations that have the potential to interbreed in nature • each species has a geographical range where individuals are concentrated in several localized populations • these populations may be isolated, rarely exchanging genetic material

11. Territory - area of home range defended Adapted from: Lederer R.J. 1984. Ecology and field biology. Menlo Park, CA.: Benjamin/Cummings. P. 237-238. territory territory Personal Space territory territory territory Private Space territory territory Home Range Home Range - any location an organism may go

14. Functions of Territories • Familiarity with area • Distribution of resources • Reduces aggression with competitors • Less Disease because less density • Environment for rearing young • Food supply

16. Types of Territory • Intraspecific • Interspecific

17. Niche • Role an organism plays in a community

18. GENE POOL the total aggregate of genes in a population at any one time

19. Total genetic availabiltiy within a population individual individual individual individual individual individual individual individual Assumes panmixis (random mating) Gene Pool

20. Gene Pool • consists of all alleles at all gene loci in all individuals of a population • for diploid species, each locus is represented twice in the genome of an individual (either homo- or heterozygous for those homologous loci

21. MICROEVOLUTION when the relative frequencies of alleles in a population change over a succession of generations

22. HARDY-WEINBERG THEOREM frequencies of alleles in a population’s gene pool remain constant over the generations unless acted upon by agents other than sexual recombination

23. HARDY-WEINBERG THEOREM • VERY LARGE POPULATIONS • ISOLATION FROM OTHER SPECIES • NO NET MUTATIONS • RANDOM MATING • NO NATURAL SELECTION

24. Hardy-Weinberg Equation p2 + 2pq + q2 = 1 Frequency Frequency Frequency of AA of Aa of aa

25. Pink and White Wildflowers • “A” represents an allele for pink • “a” represents an allele for white • diploid organism • AA = homozygous pink • Aa = heterozygous pink • aa = homozygous white • Assume 500 flowers

27. Assume 20 of the flowers are white, 480 must be pink • Assume of 480 pink, 320 are AA and 160 are Aa • 500 plants = 1000 genes for flower color • How many express “A” 320 x 2 = 640 (AA) 160 x 1 = 160 (Aa) 800 express “A” Gene Frequency = 80% or .8

28. Since there are only 2 forms of the gene, “A” and “a” and 80% are “A”, then 20% or 0.2 must be “a” • How will genetic recombination (sex) affect the gene frequencies we just calculated? • Assume sperm and egg unite completely randomly • a sperm will have 0.8 chance to contain an “A” allele and 0.2 chance to contain an “a” allele • The same for each egg

29. Product Law of Probability • Probability of picking two “A” alleles is 0.8x0.8=.64 (64%) • Thus 64% of the plants in the next generation will have genotype AA • Probability picking two “a” alleles is 0.2x0.2=0.04 (4%) • Therefore, 32% (0.32) will be “Aa”

30. Second Generation • Second generation genetic make-up will be 0.64 Aa, 0.32 Aa, and 0.04 aa • If we repeat the process, another mating would result in the same gene frequencies • Results in equilibrium of the population, referred to as Hardy-Weinberg Equilibrium

31. Hardy-Weinberg Equation • allows you to calculate frequencies of alleles in gene pools if you know frequencies of genotypes • allows you to calculate frequencies of genotypes if you know the frequencies of alleles in gene pools

32. Example What percentage of the population carries the allele for PKU (phenylketonuria)? (recessive allele) • 1 in 10,000 babies in US are born with PKU • frequency of PKU babies in US = q2 in H-W equation • q2 = 0.0001 • q = 0.01 • Frequency of dominate allele p = 1-q or 0.99

33. Carriers (pq) = 2pq or 2x0.99x0.01=0.0198 • Approximately 2% carry the PKU gene

34. Microevolution Potential Agents of Microevolution • genetic drift • gene flow • mutation • nonradom mating • natural selection

35. Genetic Drift changes in the gene pool of a small population due to chance • small populations • wildfire • floods • other types of destruction of alleles due to chance

37. Bottleneck Effect and Genetic Drift • disasters that reduce the size of a population by killing individuals unselectively • surviving population unlikely to be representative of the original population • examples in Florida are the Florida panther that has been reduced to too few breeding individuals for any type of genetic variability

39. Founder Effect When a few individuals colonize an isolated area, the small sample size will probably not represent the original population from whence it came • Darwin’s finches • retinitis pigmentosa on Tristan da Cunha(progressive loss of retinal response, atrophy, clumping of pigment)

40. Peterson Roger Tory. 1967 Apr. The Galapagos:eerie cradle of new species. National Geographic. p. 544-545.

42. Gene Flow The migration of fertile individuals or the transfer of gametes between populations • pollination from other species from another area • breeding panthers from west to those from east

43. Mutation • spontaneous • induced

44. Nonrandom Mating • inbreeding • assortative mating - individuals select partners like themselves in certain phenotypic traits

45. These beetles, Lytta magister, are found in the Sonoran Desert of Arizona. They pair off, posterior to posterior, according to size. They may continue to feed on brittlebush flowers during copulation. Copulation may last several hours.

46. Natural Selection • some organisms produce more offspring than others • salt and pepper moths

47. From: Starr Cecie. 1997. Biology: concepts and applications, 3rd ed. Belmont, CA: Worth. Microevolution; p. 229.

48. The Genetic Basis of Variation • In what ways do members of a population vary? • How extensive is that variation? • What mechanisms generate and maintain variations in a population? • Do all variations function as raw material for selection?

49. From: Starr Cecie. 1997. Biology: concepts and applications, 3rd ed. Belmont, CA: Worth. Microevolution; p. 224.

50. The Nature and Extent of Genetic Variation Within and Between Populations • people reflect individual variations in appearance and temperament • not all variation observed is heritable (some is environmental) • Discrete and quantitative contribute to variation