Lecture 4 Evolution and Life Histories

1. Lecture 4Evolution and Life Histories Principles of EcologyEbenGoodaleCollege of Forestry, Guangxi University

2. Readings • Up until now I have made reading notes for each lecture. • I will make one more of these for Tuesday lecture (my wife presenting). • It will be available Sunday night. • After that, we will have 2 chapters of textbook (ocassionally 1) per lecture.

3. Readings • The textbook chapters will be available as .xps files (10 pages per file). • I will give out today pendrives with Chapters 9-12 (Apr 4, Apr 7 lectures). • Please DO NOT give copies of these files to anyone outside of class (technically illegal). • I do not like distributing like this, but do so because textbook not distributed in China, and very expensive to buy privately.

4. Readings • Please do readings before class, because it will serve as a preparation for class. • The exam material will, however, be directly take from lectures, not the textbook. • Before the exam, I will make a summary for you on the concepts in the lectures that I will test you on. • Lecture PPTs will continue to be available before class on Thursdays and Sundays.

5. Lecture times: Schedule

6. Review I • We have been talking about how organisms interact with their environment, obtaining water, maintaining their temperature, and obtaining energy. • We have described features of organisms which are “adapted（适应）” to their environment (fit their environment due to evolution). • We have described some examples of “convergent evolution（趋同进化）”, where different organisms in similar environments look alike. Today we talk more in depth about evolution

7. Today’s class • Evolution • Evolution as change • Natural selection as mechanism of evolution • Other mechanisms of evolution • Speciation and evolutionary patterns • Life histories

8. Evolution（进化） is change • At the large time scale evolution is modification (change) in living things over time. • Contrasted with creationism, which says that: • species were developed independently of each other • species are fixed entities, they do not change • creation was recent

9. Evolution is change Things that led Darwin to believe in evolution: • Fossils • Vestigial（退化的） features • Relations between species Vestigial features have lost their function, like eyes on blind salamanders, or the human tail bone.

10. Evolution is change Things that led Darwin to believe in evolution: • Fossils • Vestigial features • Relations between species Galapagos “Darwin” finches… The birds on different islands resemble each other but also have differences.

11. Evolution is change • Contrasted with creationism, which says that: • species were developed independently of each other. Clear relationships among species. • species are fixed entities, they do not change. Fossil animals, vestigial features. • creation was recent. Evidence of ancient earth. Question: was Charles Darwin the first to postulate evolution?

12. Evolution is change • At a small time scale, evolution is the change in alleles（等位基因） (or change in gene frequencies) in a population over generations. • Example of allele controlling coat color, or beak size. An allele is an alternative version of a gene.

13. Natural selection is a mechanism of evolution • So how to explain evolution as the small time scale in a population? • Darwin postulated natural selection（自然选择）as a mechanism of evolution (this was his novel contribution). • Let’s review the basic steps in the process.

14. Natural selection What are the basic steps in this process: • Variation between individuals in traits • This variation is the trait is heritable（可继承的） • In every generation, there are more offspring produced than can survive. • Individuals with traits that fit the environment well survive and reproduce. • More individuals in the next generation will have the favored trait.

15. An important distinction:phenotype vs. genotype • We see that the first ingredient for natural selection is variation, and we note that if variation is hereditary, natural selection will occur. • BUT not all variation is genetic. Some of how an organism appears (its phenotype（表现型）) is environmental. Think of a large, spreading tree in a good sunny place, compared to one in the middle of a forest. • We should keep in mind that phenotypic plasticity（表现型可塑性）can explain variation among individuals. • What human examples can you think of? This book tells story of identical twins separated at birth

16. Natural selection in action Darwin’s Finches Images from: Freeman and Herron (2001)

17. Natural selection in action Peter and Rosemary Grant Daphne Major Beak of the Finch 1995 By J. Weiner

18. Natural selection in action 1. Variation between individuals in traits Images from: Freeman and Herron (2001)

19. Natural selection in action 2. This variation is heritable Images from: Freeman and Herron (2001)

20. Natural selection in action 3. In every generation, there are more offspring produced than can survive. # Birds 1975 1979 # Seeds Images from: Freeman and Herron (2001)

21. Natural selection in action 4. Individuals with traits that fit the environment well survive and reproduce. 5. More individuals in the next generation will have the favored trait. Large seeds Characteristic of seeds Small seeds Images from: Freeman and Herron (2001)

22. Natural selection in action 1976 4. Individuals with traits（特质） that fit the environment well survive and reproduce. 5. More individuals in the next generation will have the favored trait. 1978 Images from: Freeman and Herron (2001)

23. Review: using another example, explain how evolution occurred Weight of sheep Horn length 1975 2005 Year

24. Wild type A A G G G G A U U U C U A A U mRNA 5 3 Lys Protein Met Phe Gly Stop Amino end Carboxyl end Base-pair substitution No effect on amino acid sequence U instead of C A U G A A G U U U G G U U A A Lys Met Phe Gly Stop Missense A instead of G A A U G A A G U U U A G U U A Lys Met Phe Ser Stop Nonsense U instead of A G A A G G U U G A A U U U U C James Watson and Francis Crick, 1953 Met Stop What Darwin didn’t know: genetics and mutations. • We now know that genetic information is encoded in DNA. • Mistakes in DNA copying make mutations（突变）, which create variation. The simplest kind of mutation: a point mutation where one nucleotide replaced by another.

25. What Darwin didn’t know: genetics and mutations. • Mutations can also be larger: like the deletion of entire parts of a chromosome. • In addition to mutation, recombination（重组）, which occurs during sexual reproduction, also produces variation

26. Mutation as an evolutionary force • Mutation and recombination produce variation among individuals, the first ingredients for natural selection. • Mutation can also be thought of as a mechanism of evolution because it creates new alleles.

27. Another evolutionary force: genetic drift Before After Genetic drift（基因漂变）is the change in the frequency of alleles in a population over time through random events

28. Genetic drift Demonstration of Genetic drift in simulation: http://sites.sinauer.com/ecology3e/problem06.html Genetic drift is more important factor in small populations than large ones. Cheetahs are an example of a small population One example of genetic drift is when a species gets very rare “Bottleneck” Or when a small group of individuals starts a new colony

29. Another evolutionary force: gene flow • Gene flow（基因流）is when alleles move between populations. • Because it tend to make populations more similar to each other, it acts to slow evolution.

30. Summary of evolutionary forces • Natural selection: increases frequency of advantageous alleles. • Mutation: creates new alleles. • Genetic drift: change in frequency of alleles, can lose to loss of alleles in small populations. • Gene flow: movement of alleles between populations. Tends to decrease changes in alleles. Only one of these mechanisms of evolution leads to adaptation. Which is it?

31. Only natural selection creates adaptations • Adaptation is the match of an organism to its environment. • A great example is the story of the Soapberry Bugs. The length of beak of soapberry bugs in different populations

32. There are limit to adaptations • There needs to be the variation for natural selection to work with. • The history of animals limits their possibilities. For example, mammals that return to the sea (dolphins) can’t just evolve the ability to breathe under water. • Gene flow often acts against adaptation. • The environment is itself changing… so there’s a “moving target”. Nor can a panda immediately evolve an opposable thumb.

33. What does natural selection lead to? What kind of selection was our bird example? Our sheep example?

34. Stabilizing（稳定性） selection • Idea of trade-offs www.kellymannophotography.com/ Size of babies Low birth weight often higher risk of infection High birth weight complications at birth

35. Disruptive selection www.blackwellpublishing.com Back to Darwin’s finches … what would happen if two types of seeds were available… very large and very small? T. B. Smith, Nature, 1987 This kind of natural selection is rare and may lead to speciation…

36. Speciation • Speciation（物种形成）can occur when: • Two populations become isolated • Each population undergoes evolution, usually through natural selection. • When they meet again they do not reproduce.

37. Speciation • Often occurs because these two populations are in different places (allopatric speciation（区域种化）), but can occur in same place (sympatric speciation（同域物种形成）) in some circumstances. Famous example of sympatric evolution, where one population of apple fly adapted to new invasive tree species

38. Speciation Each type of cross-bill has its own call type (so they can Recognize each other) Assortative mating How does Benkman (2003) hypothesize that speciation is occuring?

39. A phylogenetic (= evolutionary) treeshows history of speciation and extinction This recent example of whale evolution similar to ideas Darwin proposed in his notebooks in the 1850’s

40. Story of life includes periods of mass extinction, followed by adaptive radiations • In history of earth, 5 mass extinction（大量消亡）events may have removed many species. • Adaptive radiations（适应辐射）are when a group of organisms give rise to many species in a short time Adaptive radiations occur when a new niche opens up after extinction (mammals after dinosaurs), or a new place is colonized (Hawaii is formed by volcanos)

41. Evolution and ecology and linked together • Take for example, the case of predator and prey, an ecological relationship. • Over time predators become more efficient at catching prey through natural selection. • But at the same time, prey become more efficient at escaping predators! • Ecology at one instance a product of ever-changing “coevolutionary（共同进化） armsrace”.

42. Evolution and ecology and linked together • Ecology also influences evolution: • Take care for instance the soapberry bugs. • New environments (different trees) make different kinds of beaks adaptive. • Leads to two different kinds of populations and eventually speciation. • Ecological change has lead to evolution.

43. Today’s class • Evolution • Evolution as change • Natural selection as mechanism of evolution • Other mechanisms of evolution • Speciation and evolutionary patterns • Life histories（生活史）

44. The case study of Nemo We all know that movie’s are not realistic… but did you know that in real life Nemo’s father probably would have changed sex and turned into a female? Sequential （连续地）hermaphroditism（雌雄同体）

45. The diversity and complexity of lifecycles Release egg and sperm • Note : • Sexual / Asexual • life phases • Metamorphosis（变形） • Estimated 80% of • animal species undergo Colony of identical polyps Polyp reproduces asexually Small larva floating at sea Metamorphosis into attached polyp

46. The diversity and complexity of lifecycles Even more strange (to humans) because Haploid（单一的） life stages are multicellular.

47. Basic question: to be sexual or not? • Advantages asexual

48. Basic question: to be sexual or not? Advantages sexual • Sexual reproduction increases genetic variability (new combinations of genes, recombination) • Evidence from C. elegans worms

49. Life history • The study of life history looks at the timing of how organisms grow, develop, reproduce and survive until death. • Stress on trade-offs（物质交换）. For example, early reproduction often means low survival. When first reproduce? How many offspring? Size of offspring? How long survive?

50. Trade-off I: size of offspring Trade-off: the bigger your offspring, the less you can have of them. For plants: For animals: