BIOL 4120: Principles of Ecology Lecture 6: Evolution and Adaptation

1. BIOL 4120: Principles of Ecology Lecture 6: Evolution and Adaptation Dafeng Hui Office: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu

2. Introduction • Major question in Ecology: What determines distribution & abundance of species? • Two classes of answers • Contemporary, local and regional factors (biomes and PPT and T) • Historical factors (= evolutionary ones) • Why different species live in different environments? (Adaptation and evolution) • E.g., grasslands; long necked giraffe in savannas of Africa (widely dispersed, umbrella-shaped trees); white coated polar bear in Arctic (invisible to prey)

3. Evolutionary Ecology (Chapter 6) • 6.1 Phenotype is the outward expression of an individual’s genotype • 6.2 Adaptations result from natural selection on heritable variation in traits that affect evolutionary fitness • 6.3 Evolutionary changes in allele frequencies have been documented in natural populations • 6.4 Individuals can respond to their environments and increase their fitness • 6.5 Phenotypic plasticity allows individuals to adapt to environmental change

4. 6.1 Phenotype is the outward expression of an individual’s genotype Review concepts in Genetics: 1. Gene and genetic variation 2. Phenotype and genotype 3. Sources of genetic variation 4. Qualitative and quantitative traits

5. What are genes? Genes: discrete subunit of chromosome, carry genetic information Chromosomes: the threadlike structures where DNA is contained DNA: Deoxyribonucleric acid. All DNA is composed of the same 4 nucleotide (ATGC), differ in sequence. Alleles: different forms of a gene (A, a). Locus: the position of an allele occupies on a chromosome Homozygous (AA, aa) vs heterozygous (Aa) Dominance (A vs a), incomplete dominance (Aa shows different trait to AA or aa)

6. How are genes transmitted? Genotype: the sum of genes carried by the individual. Gene pool: total collection of genes across all individual in the population at any one time Phenotype: the observed expression of genotype (color etc)

7. Phenotypic plasticity Phenotypic plasticity: the capability of an individual to exhibit different responses and produce a range of phenotypic expressions under different environmental conditions.

8. Sources of genetic variation Genetic variation within a population is absolutely necessary for natural selection to occur If all individuals are identical within a population then their fitness will all be the same

9. Sources of genetic variation • Mutation: inheritable changes in a gene or a chromosome • Gene mutation: (point mutation) such as sickle-cell anemia, cystic fibrosis • Chromosome mutation • deletion, duplication, inversion, translocation • Genetic recombination Sexual reproduction two individuals produce haploid gametes (egg or sperm) – that combine to form a diploid cell or zygote. • Reassortment of genes provided by two parents in the offspring • Increases dramatically the variation within a population by creating new combinations of existing genes. Asexual reproduction: less variation (only mutation)

10. Genetic basis of continuously varying phenotypic traits Many phenotypic traits show continuous variation (quantitative traits). Traits such as sizes and rates of processes are often influenced by many genes.

11. 6.2 Adaptation result from natural selection on heritable variation in traits that affect evolutionary fitness • Evolution pertains to any changes in a population’s gene pool. When genetic factors cause differences among individuals in survival and reproductive success, evolutionary change comes about through natural selection. Individuals whose traits enable them to achieve higher rates of reproduction leave more descendants, and therefore the alleles responsible for those traits increase in the gene pool of the population. • The process is often referred to as Adaptation.

12. Evolution by natural selection What is Darwin’s natural selection? The differential success (survival and reproduction) of individuals within the population that results from their interaction with their environment. “Survival of fitness, elimination of ‘inferior’ individual”

13. Three main ingredients of evolution by natural selection: • 1. There is variation among individuals in a population. • 2. The Variation is heritable. • 3. Differences in survival and reproductive success, or fitness, related to that variation. • Survival and reproduction are not random, but are related to variation among individuals. Organisms with best characteristics are ‘naturally selected.’ If 3 conditions are met, the population will change from one generation to the next. Evolution will occur.

14. One example: Evolutionary change in a population may result from a change in the environment. Cyanide fumigation to kill scale insects Initially, very effective, killed most non cyanide-resistant individuals Fumigation was not effective Natural and artificial selection (crops, domestic animals)

15. Evidence of natural selection • Evolution of beak shape in Finches. • Peter and Rosemary Grant’s (and colleagues) work on Medium Ground Finch Geospiza fortis.

16. Natural selection • Darwin’s Finches • Genetic studies show all arise from a single ancestral species.

17. 40-ha Daphne Major island Rosemary & Peter Grant

18. Is there a phenotypic variation in beak size?

19. Is variation in beak size correlated with variation in fitness? In 1978, there was a severe drought due to La Nina, small seeds declined more than large seeds. Small beak birds have difficulty to find seeds, and suffered heavy mortality, especially females.

20. Beak size evolves post-drought pre-drought Conclusion: Nature selection indeed caused evolution in beak size

21. Three types of selection

22. Disruptive selection increases phenotypic variation in a population Black bellied seedcraker

23. 6.3 Evolutionary changes in allele frequencies have been documented in natural populations • Cyanide resistance in scale insects • Pesticide and herbicide resistance among agricultural pests • Antibiotic resistance among pathogenic bacteria (superbug)

24. Selection and change in frequency of melanistic moths Birds eaten Normal Melanistic Unpollu- ted woods 26 164 Polluted 43 15 woods Kettlewell (1950s) Early in the nineteenth century, occasional dark, or melanistic, speciemens of the peppered moth were collected. Over the next hundred years, this dark form became increasing common in forests near heavily industrialized region  industrial melanism.

25. England, started pollution control in the 1950s

26. 6.4 Individuals can respond to their environments and increase their fitness Evolution occurs through the replacement of less fit individuals by the progeny of more fit individuals in a population over time. Individuals do not benefit from evolution. It is the gene pool of the population evolves, not individuals. But individuals can undergo certain changes over space and time and respond to the environmental changes. E.g.: Global change or urbanization. Animal: can move around. Microhabitaes and microenvironments. Example: Responses of Catcus wren to microhabitats.

28. BIOL 4120: Principles of Ecology Lecture 6: Evolution and Adaptation Dafeng Hui Office: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu

29. Recap Evolution by natural selection Example of national selection: Beak size Three types of selection Individuals can respond to environmental changes

30. 6.5 Phenotypic plasticity allows individuals to adapt to environmental change The set of phenotype expressed by a single genotype across a range of environmental conditions is referred to as the norm of reaction Reaction norm.

31. Norm of reaction The set of phenotype expressed by a single genotype across a range of environmental conditions is referred to as the norm of reaction.

32. The reaction norms of populations adapted to different environments may differ Caterpillars of swallowtail butterfly were obtained from two populations: one from Alaska and one in Michigan. Grow in two temperature conditions High T stimulated growth, but in cold T, caterpillars from Alaska grow better under lower T.

33. Norm of reaction

34. Reaction norms may be modified by evolution Reaction norms may diverge when two populations of the same species exist for long periods under different conditions. Very often, an increase in performance under prevalent conditions is accompanied by a decrease in performance when exposed to conditions outside the population’s normal range .

35. Acclimation Adaptive phenotypic plasticity referred to as Acclimation, such as growing thicker fur in winter, producing smaller leaves during the dry season, producing enzymes with different T optima at different temperatures. Acclimation may be thought as a shift in an individual’s range of physiological tolerances. It is useful in response to seasonal and other persistent changes in conditions Acclimation may takes days to weeks Acclimation is reversible

36. Blue: 20oC Red: 45oC Larrea: creosote bush, subtropical desert plant, photosynthesis in both winter and summer Atriplx: saltbush, native to cool coastal region of CA Tidestromia: heat-loving, thermophilic species

37. Irreversible developmental responses Development responses: When conditions persist for long periods, the environment may influence individual development so as to modify the size or other attributes of the individual for long periods, even for its remaining life time. These changes are referred to as Development Responses Coloration of African grasshopper

38. Development responses are not reversible Water fleas Left was exposed to predators and survived, with a helmet.

39. Genotype-environment interaction Phenotypes = Genotypes + Environments How to test if phenotypic variation is due to genotype or environments? Reciprocal transplant experiments

40. Reciprocal transplant experiment are used to investigate the causes of differences between populations

41. The growth rate of fence lizards reveal both genetic determination and phenotypic plasticity

42. The End