1. BIOL 4120: Principles of Ecology Lecture 2: Adaptation and Evolution
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BIOL 4120: Principles of Ecology Lecture 2: Adaptation and Evolution
Dafeng Hui
Office: Harned Hall 320
Phone:

2. 2.1 Nature selection as a force of evolution
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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
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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
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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”
Fitness of an individual is measured by the proportionate contribution it makes to future generations.
Fitness is “reproduction”
Selection works on population, not individual.

5. Two conditions (assumptions):
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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
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Evidence of natural selection
Evolution of beak shape in Finches.
Peter and Rosemary Grant’s (and colleagues) work on Medium Ground Finches Geospiza fortis.
Do we have any evidence of NS? (Domestic animal, crops Natural+articifical selection?)
webbed foot of a duck enables it to swim better than a foot that is not webbed.
There are two forms of the peppered moth (Biston betularia) in England- a dark-colored form (carbonaria) and a light form (typica).

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

8. 4/19/2017
40-ha Daphne Major island
Rosemary & Peter Grant

9. Is there a phenotypic variation in beak size?
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Is there a phenotypic variation in beak size?

10. Is variation in beak size correlated with variation in fitness?
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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
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Beak size evolves
post-drought
pre-drought
Conclusion: Nature selection indeed caused evolution in beak size

12. Types of natural selection
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Types of natural selection
Stabilizing selection: human birth weight.
Black bellied seedcraker: feed on seeds of two species of sedge. Seeds are same in size, but differ in hardness. Large beak on hard seed, small on soft seeds.
black bellied seed cracker beak size

13. 2.2 Heritability is an essential feature of NS
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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
For NS to occurs, the first thing is inheritable variation. “Blending inheritance” before Mendel.

14. Mendle’s Pea experiment
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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
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2.3 Genes are the units of inheritance

16. 4/19/2017
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)
At any locus, diploid individuals have two copies of genes (alleles).

17. How are genes transmitted?
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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)
Flower color is controlled by one gene, two alleles. P and W. (Picture was cut somehow, differ from textbook)
Gametes: egg or sperm

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

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

20. 2.4 Genetic variation is the ingredient for Natural Selection
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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
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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?
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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
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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
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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
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26. Five Causes of evolution
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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
Gene frequency: any thing influencing gene f will

27. One Example: Genetic drift in a small population
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One Example: Genetic drift in a small population

28. 4/19/2017
Flooding

29. 2.6 Speciation and mechanisms
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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)
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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
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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
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Allopatric Speciation
Geographic isolation, Easy to understand.
The following concepts mentioned in the textbook.
Cline: measurable, gradual change over a geographic region in the average of some phenotypic charter, such as size, coloration or a gradient genotypic frequency. Example, weight change of White-tailed deer, 136 kg in Canada, 93 kg in Kansa, 46 in Louisiana.
Ecotype: a population adapted to local environmental conditions (step clines). Examples, Yarrows from high elevation to low elevation. Short Stature from high elevation retained no matter where planted.
Geographic isolates (subspecies): distinguishable by certain characters, but there is gene flow between them. First stage of speciation.

33. Allopatric speciation: Ring species
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Allopatric speciation: Ring species
salamander
San Joaquin Valley, CA
Ring species: population of a single species encircle an area of unsuitable habitat. As a result, the species becomes geographically distributed in a circular, or ring, pattern over a large geographic area.

34. Speciation via geographic isolation and divergence
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Speciation via geographic isolation and divergence

35. Sympatric speciation (e.g: Speciation by Polyploidy)
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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
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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.

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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.

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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. 4/19/2017
The End

40. Brief history of integration of Genetics into Ecological studies
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Natural Selection—Darwin (1859) The Origin of Species
Particulate genetics & inheritance—Gregor Mendel ( )
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
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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. Three types of selection
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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
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Fig. 5-6 An example of microevolution – directional selection

44. Summary What is natural selection? Different types of NS
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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
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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
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Geographical isolates
Salamanders

47. Adaptations of Honeycreepers on the island of Hawaii
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Adaptations of Honeycreepers on the island of Hawaii

48. Recap What’s Nature selection? 2 assumptions?
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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