1. 33-1 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Chapter 33: Mechanisms of evolution

2. 33-2 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Populations and their gene pools Population –group of individuals of the same species, usually occupying a defined habitat –over one or more generations, genes can be shared through entire range of population –asexual populations more difficult to define  characterised by similarities in phenotype Gene pool –sum of all genes in a population at a given time

3. 33-3 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Species –many concepts proposed to define a species Biological species concept –groups of actually or potentially interbreeding natural populations which, under natural conditions, are reproductively isolated from other such groups (definition proposed by Mayr and others) Other species concepts emphasise different aspects

4. 33-4 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Evolutionary change Microevolution –change in gene pools –natural selection  change due to impact of environment –genetic drift  random change Macroevolution –change at or above the level of species  speciation

5. 33-5 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Genetic variation Genetic variation within populations drives evolution Variation arises from –mutation –recombination

6. 33-6 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Mutation Spontaneous or induced change in DNA sequence –minor (e.g. nucleotide substitutions, deletions) –major (e.g. chromosome inversions, translocations) Effect of mutation is expressed in phenotype –neutral  no effect –disadvantageous  negative effect (reduces fitness) –advantageous  positive effect (increases fitness)

7. 33-7 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Measuring genetic variation Methods of detecting and measuring genetic variations –phenotypic frequency –genotypic frequency –allele frequency

8. 33-8 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Phenotypic frequency Some phenotypic traits allow a population to be characterised genetically –variation in phenotype is directly related to genotype –genetic markers Variations (polymorphisms) in phenotypic trait are controlled by different alleles –example: Rhesus (Rh) blood groups in humans  Rh+ (dominant)  Rh– (recessive)

9. 33-9 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Genotypic frequency Where dominance exists, phenotypic frequency gives incomplete information about allele frequency –recessive allele gives rise to phenotype when individuals are homozygous –dominant allele gives rise to same phenotype whether individuals are homozygous or heterozygous Immunological tests identify allele combinations –distinguish between homozygous and heterozygous individuals

10. 33-10 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Allele frequency Calculate frequencies with which certain alleles occur –proportion of total alleles –does not indicate combinations p + q = 1 where p and q are frequencies of each allele

11. 33-11 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Hardy–Weinberg principle Model of relationship between allele and genotypic frequencies Phenotypic frequencies in a population tend to remain constant at equilibrium values that can be estimated from allele frequencies Hypothetical ideal population –equilibrium established after one generation

12. 33-12 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Hardy–Weinberg equation Allows genotypic frequencies to be calculated from phenotypic frequencies –where dominance exists p 2 + 2pq + q 2 = 1 –calculate frequencies from q 2 (homozygous recessive)

13. 33-13 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Hardy–Weinberg assumptions Individuals mate at random The population is so large that it is not affected by genetic drift No mutation No migration No natural selection

14. 33-14 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Microevolution Hardy–Weinberg assumption: Individuals mate at random Random mating –trait has no effect on mate choice Assortative mating –trait has an effect on mate choice –phenotypically similar mates  positive assortative mating –phenotypically dissimilar mates  negative assortative mating

15. 33-15 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Genetic drift Hardy–Weinberg assumption: The population is so large that it is not affected by genetic drift Chance of microevolutionary change in a population’s gene pool –some alleles are lost –other alleles become fixed In small populations, the chance of genetic drift is high

16. 33-16 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Mutation and migration Hardy–Weinberg assumption: No mutation Mutation introduces novel genetic variation and new alleles Hardy–Weinberg assumption: No migration Migration can change composition of gene pools if different groups exhibit different allele frequencies

17. 33-17 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Natural selection Hardy–Weinberg assumption: No natural selection Natural selection acts on phenotypes Changes frequencies of genotypes that give rise to those phenotypes –fitter genotypes appear in greater proportion to less fit genotypes Moves allele frequencies away from equilibrium

18. Question 1: For a trait controlled by a single locus with two alleles which shows incomplete dominance, how many phenotypes are possible? a) One b) Two c) Three d) Four e) Five 33-18 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University

19. 33-19 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Natural selection (cont.) 1.More individuals are produced each generation than can survive to have offspring themselves –some individuals die before they reach breeding age –what determines which die and which survive? 2.Variation exists between individuals in a population and some of this variation involves differences in fitness –fitness is an organism’s ability to survive (viability) and produce the next generation (fertility) –some individuals have greater fitness than others

20. 33-20 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Natural selection (cont.) 3.Fitter individuals make a relatively greater contribution to the next generation than the less fit individuals –fitter individuals produce more offspring than others 4.Differences in fitness between individuals are inherited –reproducing individuals pass on their characteristics to the next generation

21. 33-21 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Natural selection (cont.) Fitter individuals reproduce more successfully than less fit individuals Contribute proportionately more to the next generation Cumulative effect over generations –results in change in gene pool

22. 33-22 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Speciation and species concepts Speciation is the process by which new species are formed Defining the concept of species is complex and no single species concept is universally accepted –biological species concept –taxonomic or morphological species concept –recognition species concept –evolutionary species concept –cohesion species concept

23. 33-23 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Species concepts Biological species concept –‘groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups’ –does not consider morphologically different species that can interbreed to produce hybrids or asexually- reproducing species Taxonomic species concept –species is defined by phenotypic distinctiveness –members of a species are morphologically alike –problems with convergence and mimicry

24. 33-24 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Species concepts (cont.) Recognition species concept –species are groups sharing a common mate recognition system –does not consider asexually reproducing species Evolutionary species concept –a species is a lineage of populations delineated by common ancestry and able to remain separate from other species Cohesion species concept –species have mechanisms for maintaining phenotypic similarity, including gene flow and developmental constraints

25. 33-25 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Reproductive isolation All species concepts consider reproductive isolation (prevention of gene flow between species) to be an important factor in maintaining a species’ integrity Reproductive isolating mechanisms inhibit or prevent gene flow between species –ecological isolation –temporal isolation –ethological isolation –mechanical isolation –gametic isolation –postzygotic isolation

26. 33-26 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Reproductive isolation (cont.) Ecological isolation –species do not hybridise because they occupy different habitats Temporal isolation –species do not hybridise because they are not ready to mate at the same time –example: two plant species produce flowers at different times Ethological (behavioural) isolation –species do not recognise each other as potential mates because the courtship patterns differ between species –example: frogs of different species have different mating calls

27. 33-27 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Reproductive isolation (cont.) Mechanical isolation –species do not hybridise because reproductive structures differ –example: differences in pedipalps of male spiders Gametic isolation –species do not hybridise because sperm are inviable in female reproductive tract, do not recognise egg of other species or cannot enter egg Postzygotic isolation –species may produce hybrids but hybrids are inviable or are sterile

28. Question 2 Which of the following is not an example of a pre- mating reproductive isolating mechanism? a) Temporal isolation b) Mechanical isolation c) Use of different sex attractant pheromones in butterflies d) Ecological isolation e) Incompatible sperm and ova 33-28 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University

29. 33-29 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Allopatric speciation Populations of ancestral species are split by geographical barrier –inhibits migration and disrupts gene flow between populations Divergence of populations due to natural selection and genetic drift Reproductive isolation may develop, so if populations were to be reunited, gene flow would not be re-established

30. 33-30 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Fig. 33.17: Models of speciation (a)

31. 33-31 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Parapatric speciation Parapatric speciation occurs in adjacent populations Geographical ranges are in contact, but selection exerts different pressures on populations Eventually gene flow is interrupted and populations become reproductively isolated

32. 33-32 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Fig. 33.17: Models of speciation (cont.) (b)

33. 33-33 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Sympatric speciation Sympatric speciation takes place without geographical separation of populations Disruption of gene flow occurs when groups of individuals become reproductively isolated from other members of the population Polyploidy is a mechanism by which this occurs –multiple sets of chromosomes –common in plants –also found in some animals

34. 33-34 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Fig. 33.17: Models of speciation (cont.) (c)

35. 33-35 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Hybridisation Not all hybrids are inviable or sterile Hybrids between species may become parthenogenetic –produce young from eggs without fertilisation Avoids problems of chromosome pairing with mismatched sets of chromosomes –example: parthenogenetic triploid gecko Heteronotia binoei formed by two hybridisation events

36. 33-36 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Copyright © Craig Moritz, University of Queensland Fig. 33.21: Origin of Heteronotia binoei

37. 33-37 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Fig. 33.24: Origin of Heteronotia binoei (cont.) Copyright © Craig Moritz, University of Queensland

38. 33-38 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University Molecular evolution Molecular sequences have diverged from a common ancestral sequence Gene duplication and sequence divergence produces gene families Homologous genes are derived from a common ancestral gene –orthologous genes arise when a species with the ancestral gene splits into two species –paralogous genes arise by gene duplication in a line of descent

39. Summary Evolution is the process of genetic change in a population over time Evolution results in individuals who are able to survive and reproduce in their environment well enough to produce viable offspring Biological evolution requires heritable variation and a force to act on this variation Natural selection occurs when individuals with heritable differences show differences in survival and reproduction. 33-39 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University

40. Summary (cont.) Heritable traits from fitter individuals become more numerous in a population over time Natural selection may act differently on males and females in the same population Co-operation between individuals in a population can increase their inclusive fitness Speciation usually involves physical, ecological or temporal isolation of populations, which diverge over time 33-40 Copyright  2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University