BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 6: Evolution and Lecture 6: Evolution and AdaptationAdaptation

Dafeng HuiDafeng Hui

Office: Harned Hall 320Office: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: dhui@tnstate.edu

Introduction Introduction

Major question in Ecology: What determines Major question in Ecology: What determines distribution & abundance of species?distribution & abundance of species?

Two classes of answersTwo classes of answers• Contemporary, local and regional factors

(biomes and PPT and T)• Historical factors (= evolutionary ones)

Why different species live in different Why different species live in different environments? (Adaptation and environments? (Adaptation and evolution)evolution)

E.g., grasslands; long necked giraffe in E.g., grasslands; long necked giraffe in savannas of Africa (widely dispersed, savannas of Africa (widely dispersed, umbrella-shaped trees); white coated umbrella-shaped trees); white coated polar bear in Arctic (invisible to prey)polar bear in Arctic (invisible to prey)

Evolutionary Ecology (Chapter 6)Evolutionary Ecology (Chapter 6)

6.1 Phenotype is the outward expression of an 6.1 Phenotype is the outward expression of an individual’s genotypeindividual’s genotype

6.2 Adaptations result from natural selection 6.2 Adaptations result from natural selection on heritable variation in traits that affect on heritable variation in traits that affect evolutionary fitnessevolutionary fitness

6.3 Evolutionary changes in allele frequencies 6.3 Evolutionary changes in allele frequencies have been documented in natural populationshave been documented in natural populations

6.4 Individuals can respond to their 6.4 Individuals can respond to their environments and increase their fitnessenvironments and increase their fitness

6.5 Phenotypic plasticity allows individuals to 6.5 Phenotypic plasticity allows individuals to adapt to environmental changeadapt to environmental change

6.1 Phenotype is the outward 6.1 Phenotype is the outward expression of an individual’s expression of an individual’s

genotypegenotype

Review concepts in Genetics:

1. Gene and genetic variation

2. Phenotype and genotype

3. Sources of genetic variation

4. Qualitative and quantitative traits

What are genes?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)

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)

How are genes transmitted?How are genes transmitted?

Phenotypic plasticityPhenotypic plasticity

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

Sources of genetic variationSources of genetic variation

Genetic variation within a population is Genetic variation within a population is absolutely necessary for natural selection to absolutely necessary for natural selection to

occuroccur

If all individuals are identical within a population If all individuals are identical within a population then their fitness will all be the samethen their fitness will all be the same

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)

Genetic basis of continuously Genetic basis of continuously varying phenotypic traitsvarying phenotypic traits

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

6.2 Adaptation result from natural 6.2 Adaptation result from natural selection on heritable variation in selection on heritable variation in

traits that affect evolutionary fitnesstraits that affect evolutionary fitness Evolution pertains to any changes in a population’s Evolution pertains to any changes in a population’s

gene pool. When genetic factors cause differences gene pool. When genetic factors cause differences among individuals in survival and reproductive among individuals in survival and reproductive success, evolutionary change comes about through success, evolutionary change comes about through natural selection. Individuals whose traits enable natural selection. Individuals whose traits enable them to achieve higher rates of reproduction leave them to achieve higher rates of reproduction leave more descendants, and therefore the alleles more descendants, and therefore the alleles responsible for those traits increase in the gene responsible for those traits increase in the gene pool of the population. pool of the population.

The process is often referred to as Adaptation.The process is often referred to as Adaptation.

Evolution by natural selectionEvolution by natural selection

What is DarwinWhat is Darwin’’s natural selection?s natural selection?

The differential success (survival and The differential success (survival and reproduction) of individuals within the reproduction) of individuals within the population that results from their interaction population that results from their interaction with their environment.with their environment.

““Survival of fitness, elimination of Survival of fitness, elimination of ‘‘inferiorinferior’’ individualindividual””

Three main ingredients of evolution by Three main ingredients of evolution by natural selection:natural selection:

1. There is variation among individuals in a 1. There is variation among individuals in a population. population.

2. The Variation is heritable. 2. The Variation is heritable. 3. Differences in survival and reproductive success, 3. Differences in survival and reproductive success,

or fitness, related to that variation. or fitness, related to that variation. Survival and reproduction are not random, but are Survival and reproduction are not random, but are

related to variation among individuals. Organisms related to variation among individuals. Organisms with best characteristics are with best characteristics are ‘‘naturally selected.naturally selected.’’

If 3 conditions are met, the population will change If 3 conditions are met, the population will change from one generation to the next. Evolution will from one generation to the next. Evolution will occur.occur.

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)

Evidence of natural selectionEvidence of natural selection

Evolution of beak shape in Finches.Evolution of beak shape in Finches.

Peter and Rosemary GrantPeter and Rosemary Grant’’s (and s (and colleagues) work on Medium Ground colleagues) work on Medium Ground Finch Finch Geospiza fortis.Geospiza fortis.

Natural Natural selectionselection

DarwinDarwin’’s s FinchesFinches

Genetic Genetic studies show studies show all arise from all arise from a single a single ancestral ancestral species.species.

Rosemary & Peter Grant

40-ha Daphne Major island

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

Is variation in beak size correlated with Is variation in beak size correlated with variation in fitness?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.

Beak size evolvesBeak size evolves

pre

-dro

ught

po

st-d

roug

ht

Conclusion: Nature selection indeed caused evolution in beak size

Three types of selection

Disruptive selection increases phenotypic variation in a population

Black bellied seedcraker

6.3 Evolutionary changes in allele 6.3 Evolutionary changes in allele frequencies have been documented in frequencies have been documented in

natural populationsnatural populations

Cyanide resistance in scale insectsCyanide resistance in scale insects Pesticide and herbicide resistance Pesticide and herbicide resistance

among agricultural pestsamong agricultural pests Antibiotic resistance among Antibiotic resistance among

pathogenic bacteria (superbug)pathogenic bacteria (superbug)

Selection and change in frequency of melanistic moths

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.

Birds eaten

Normal Melanistic

Unpollu- ted woods 26 164

Polluted 43 15woods

Kettlewell (1950s)

England, started pollution control in the 1950s

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.

BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 6: Evolution and Lecture 6: Evolution and AdaptationAdaptation

Dafeng HuiDafeng Hui

Office: Harned Hall 320Office: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: dhui@tnstate.edu

RecapRecap

Evolution by natural selectionEvolution by natural selection

Example of national selection: Beak sizeExample of national selection: Beak size

Three types of selectionThree types of selection

Individuals can respond to environmental Individuals can respond to environmental changeschanges

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.

Norm of reactionNorm 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.

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.

Norm of reactionNorm of reaction

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 .

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

Larrea: creosote bush, subtropical desert plant, photosynthesis in both winter and summerAtriplx: saltbush, native to cool coastal region of CATidestromia: heat-loving, thermophilic species

Blue: 20oCRed: 45oC

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

Development responses are not reversible

Water fleas

Left was exposed to predators and survived, with a helmet.

Genotype-environment interaction

Phenotypes = Genotypes + Environments

How to test if phenotypic variation is due to genotype or environments?

Reciprocal transplant experiments

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

populations

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

The EndThe End