BIOL 4120: Principles of Ecology Lecture 2: Adaptation and Evolution

1. BIOL 4120: Principles of Ecology Lecture 2: Adaptation and Evolution Dafeng Hui Office: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu

2. Evolutionary Ecology • 2.1 Nature selection as a force of evolution • 2.2 Heritability is the feature of Natural Selection • 2.3 Genes are the units of inheritance • 2.4 Genetic variation is the ingredient of NS • 2.5 Evolution is the outcome of NS resulted from gene frequency change • 2.6 Speciation and mechanisms

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

4. 2.1 Nature selection as a force of evolution 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”

5. Two conditions (assumptions): • 1. There is variation in populations. Variation is heritable. • 2. In every generation some organisms are more successful at surviving and reproducing than others. Survival and reproduction are not random, but are related to variation among individuals. Organisms with best characteristics are ‘naturally selected.’ If 2 conditions are met then the population will change from one generation to the next. Evolution will occur.

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

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

8. 40-ha Daphne Major island Rosemary & Peter Grant

9. Is there a phenotypic variation in beak size?

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

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

12. Types of natural selection black bellied seed cracker beak size

13. 2.2 Heritability is an essential feature of NS • Heritability: individual’s characteristics are passed from one generation to the next. Measured as proportion of the variation in a trait in a population that is due to variation in genes. • Mendel’s genetics and inheritance

14. Mendle’s Pea experiment • Mendle’s conclusions: • Flower color is a heritable trait • For each inherited char, an organism has two units, one from each parent • (one each from egg and sperm). The unit may be the same or different. • 3. When the two units are different, one is fully expressed, another one has no • noticeable effect of the organism’s outward appearance. • Dominant: the unit is expressed (purple) • Recessive: not expressed (white).

15. 2.3 Genes are the units of inheritance

16. 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: alternate 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)

17. 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)

18. Phenotypic plasticity Phenotypic plasticity: the ability of a genotype to give a range of phenotypic expressions under different environmental conditions.

19. Norm of reaction The set of phenotype across a range of environmental conditions.

20. 2.4 Genetic variation is the ingredient for Natural Selection 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

21. Sources of genetic variation • Mutation: inheritable changes in a gene or a chromosome • Gene mutation: (point mutation) • 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)

22. What do we mean by genetic variation? • Range (variance) of phenotypes, as in Darwin’s Finch example • Different chromosomal arrangements (cytogenetics) • DNA sequence differences among individuals • Electrophoresis--> electromorphs = allozymes • Molecular marks: RFLP, RAPD, etc.

23. 2.5 Evolution is a change in gene frequency • Evolution is a change of gene frequencies within a population (or species) over time • Individuals do not evolve, populations evolve • Focus on gene pool, collective • But why do we see populations are still the ‘same’ over many generations?

24. The Hardy-Weinberg Principle • The Hardy-Weinberg Principle: Gene frequencies will remain the same in successive generations of a sexually reproducing population if the following five conditions hold: • Random mating • There is no mutation • The population is very large • There is no selection • There is no migrations (isolated from other populations)

25. The Hardy-Weinberg Principle

26. Five Causes of evolution • Mutations • Gene flow - Emigration and immigration of individuals (Flow of alleles) • Genetic Drift –Changes in the gene pool of a small population due to chance • Nonrandom mating: (AA mates AA, Aa) • Natural selection

27. One Example: Genetic drift in a small population

29. 2.6 Speciation and mechanisms • Speciation: splitting of one species into 2 different species. • Concept of species: • Biological Species: a species is a group of organisms whose individual have the potential to interbreed and produce fertile offspring. • Reproductively isolated: don’t produce fertile hybrids • Natural conditions: artificial breeding doesn’t count. For example, artificial insemination, keeping 2 species locked up together. • Morphological species: members of the same species look similar to each other. Many examples of organisms that look similar but can’t produce fertile offspring. • No one species concept applies to all organisms Flickers

30. Genetic isolation mechanisms (reproductive barriers) • Premating mechanisms • Habitat selection; temporal isolation; behavior or mechanical or structure incompatibility • Postmating mechanisms • Genetic barrier such as hybrids are sterile; seed abortion; hybrid inviability.

31. Mechanisms of speciation • Several are well documented: • Allopatric speciation (probably most vertebrates) • allopatric species occupy areas separated by time or space. • Sympatric speciation (especially plants and insects) • Sympatric species occupy the same place at the same time

32. Allopatric Speciation • Geographic isolation, Easy to understand.

33. Allopatric speciation: Ring species salamander San Joaquin Valley, CA

34. Speciation via geographic isolation and divergence

35. Sympatric speciation (e.g: Speciation by Polyploidy) • About half of all flowering plants are polyploid: more than 2 copies of each gene. • Polyploids are the result of failure of cell division (mitosis or meiosis) to separate the chromosomes into 2 cells.

36. 2.4 Adaptations reflect trade-offs and constraints Adaptation: Individuals of a species have certain characteristics that enable an organism to thrive in a given environment. Adaptations maintain or increase fitness of an organism in a given environmental conditions.

37. Tradeoff • Evolution is reflected in changes in gene frequencies and phenotypes • However, changes in gene frequencies involve tradeoffs • Giraffes do not graze well on grass due to their long necks • Snow leopards can hide in snowy mountains, ordinary leopards can hide well in green trees.

38. Constraint • There are many other factors that can influence species adaptation. • For example, response of an organism to an environmental gradient such as temperature. • All these factors influence species adaptation.

39. The End

40. Brief history of integration of Genetics into Ecological studies • Natural Selection—Darwin (1859) The Origin of Species • Particulate genetics & inheritance—Gregor Mendel (1856-1864) • Mutations & chromosomes—Hugo Devries & others (1901)--sources of variation in populations; rediscovery of Mendel’s work • “The Modern Synthesis” (Dobzhansky, Wright, Fisher, Haldane, Mayr, Simpson--1930s & 1940s) • Integration Natural Selection & mutation; genetic drift; migration • Appreciation of genetic variation within populations in nature • DNA structure/importance elucidated by Watson & Crick (1953) double helix structure of DNA • Molecular variation in natural populations (Harris; Lewontin & Hubby 1966)--using starch gel electrophoresis  molecular biology. • Synthesis of Ecology with Genetics --> Evolutionary Ecology (starting in 1970s)!

41. Evolution by Natural Selection • The major factors affecting the organisms’ survival in the system is Fitness • Darwinian fitness: ability of an organism to survive and reproduce in its environment. • Adaptation is a characteristic or trait of an organism that increases its fitness relative to individuals that do not possess it. It is an inherited characteristic that increases the ability of an organism to survive and reproduce.

42. The traits selected for by natural selection need to be inheritable so that the next generation after selection retains the change • Three types of selection • Directional • See finches • Stabilizing • Long necks in giraffes • Disruptive • Sexual dimorphism

43. Fig. 5-6 An example of microevolution – directional selection

44. Summary • What is natural selection? • Different types of NS • Gene and genetic variation • Evolution • Hardy-Weinberg principle • Concept of species. • Speciation and mechanisms • Adaptation and trade-offs

45. What is a species • Ecology is based on the idea that we can identify different groups of organisms within an ecosystem • These groups are generally called species • There are three specific means of defining a species • Morphological species concept • A species is defined as a morphologically consistent group of organisms than can be distinguished from all other species • Can fail. So called cryptic species • Biological species concept • A group of populations whose individuals can interbreed and produce fertile offspring and cannot interbreed with other species • Reproductive isolation • Still fails. If you cannot tell the individuals apart morphologically, how can you tell if they are interbreeding or not • Also, some species can interbreed and produce viable offspring • Bontebok and Blesbok in South Africa • Genetic species concept • A group of populations whose individuals have a distinct genetic makeup and who do not interbreed with others groups of populations for some reason • Bontebok and Blesbok are genetically distinct as well as being morphologically different. Do not naturally overlap in range

46. Geographical isolates Salamanders

47. Adaptations of Honeycreepers on the island of Hawaii

48. Recap • What’s Nature selection? 2 assumptions? • Three types of natural selection • Concept in genetics: gene, chromosome, DNA, allele, locus, genotype, phenotype, dominance, incomplete dominance etc