BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 2: Lecture 2: Adaptation and Adaptation and EvolutionEvolution

Dafeng HuiDafeng Hui

Office: Harned Hall 320Office: Harned Hall 320

Phone: 963-5777Phone: 963-5777

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

Evolutionary EcologyEvolutionary Ecology

2.1 Nature selection as a force of evolution2.1 Nature selection as a force of evolution 2.2 Heritability is the feature of Natural 2.2 Heritability is the feature of Natural

SelectionSelection 2.3 Genes are the units of inheritance2.3 Genes are the units of inheritance 2.4 Genetic variation is the ingredient of NS2.4 Genetic variation is the ingredient of NS 2.5 Evolution is the outcome of NS resulted 2.5 Evolution is the outcome of NS resulted

from gene frequency changefrom gene frequency change 2.6 Speciation and mechanisms2.6 Speciation and mechanisms

Introduction to evolutionary ecologyIntroduction to evolutionary ecology

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 factors (domain of

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

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

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

2.1 Nature selection as a force 2.1 Nature selection as a force of evolutionof evolution

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

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

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

Two conditions (assumptions):Two conditions (assumptions): 1. There is variation in populations. Variation is 1. There is variation in populations. Variation is

heritable. heritable. 2. In every generation some organisms are more 2. In every generation some organisms are more

successful at surviving and reproducing than others. successful at surviving and reproducing than others. 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 2 conditions are met then the population will change If 2 conditions are met then the population will change from one generation to the next. Evolution will from one generation to the next. Evolution will occur.occur.

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 Finches Finches 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, small seeds declined more than large seeds.

Small beak birds have difficult 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

Types of natural selectionTypes of natural selection

black bellied seed cracker beak size

2.2 Heritability is an essential 2.2 Heritability is an essential feature of NSfeature of NS

Heritability: individualHeritability: individual’’s characteristics s characteristics are passed from one generation to the are passed from one generation to the next. Measured as proportion of the next. Measured as proportion of the variation in a trait in a population that variation in a trait in a population that is due to variation in genes.is due to variation in genes.

MendelMendel’’s genetics and inheritances genetics and inheritance

Mendle’s conclusions:1. Flower color is a heritable trait2. 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).

Mendle’s Pea experiment

2.3 Genes are the units of 2.3 Genes are the units of inheritanceinheritance

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: 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)

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 ability of a genotype to give a range of phenotypic expressions under different environmental conditions.

Norm of reactionNorm of reaction

The set of phenotype across a range of environmental conditions.

2.4 Genetic variation is the 2.4 Genetic variation is the ingredient for Natural Selectioningredient for Natural Selection

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 variationSources of genetic variation• Mutation: inheritable changes in a gene or a chromosomeMutation: inheritable changes in a gene or a chromosome

Gene mutation: (point mutation)Gene mutation: (point mutation) Chromosome mutationChromosome mutation

• deletion, duplication, inversion, translocationdeletion, duplication, inversion, translocation

• Genetic recombinationGenetic recombination

Sexual reproductionSexual reproduction

two individuals produce haploid gametes (egg or sperm) two individuals produce haploid gametes (egg or sperm) –– that that combine to form a diploid cell or zygote. combine to form a diploid cell or zygote.

• Reassortment of genes provided by two parents in the Reassortment of genes provided by two parents in the offspringoffspring

• Increases dramatically the variation within a population by Increases dramatically the variation within a population by creating new combinations of existing genes.creating new combinations of existing genes.

Asexual reproduction: less variation (only mutation)Asexual reproduction: less variation (only mutation)

What do we mean by What do we mean by genetic variation?genetic variation?

Range (variance) of phenotypes, as in Range (variance) of phenotypes, as in DarwinDarwin’’s Finch example s Finch example

Different chromosomal arrangements Different chromosomal arrangements (cytogenetics)(cytogenetics)

DNA sequence differences among DNA sequence differences among individualsindividuals

Electrophoresis--> electromorphs = Electrophoresis--> electromorphs = allozymesallozymes

Molecular marks: RFLP, RAPD, etc.Molecular marks: RFLP, RAPD, etc.

2.5 Evolution is a change in gene 2.5 Evolution is a change in gene frequencyfrequency

Evolution is a change of gene Evolution is a change of gene frequencies within a population (or frequencies within a population (or species) over timespecies) over time• Individuals do not evolve, populations Individuals do not evolve, populations

evolveevolve

• Focus on gene pool, collectiveFocus on gene pool, collective

But why do we see populations are still But why do we see populations are still the the ‘‘samesame’’ over many generations? over many generations?

The Hardy-Weinberg PrincipleThe 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)

The Hardy-Weinberg Principle

Five Causes of evolutionFive Causes of evolution

MutationsMutations Gene flow - Gene flow - Emigration and immigration of Emigration and immigration of

individuals (Flow of alleles)individuals (Flow of alleles) Genetic Drift Genetic Drift –– Changes in the gene pool of Changes in the gene pool of

a small population due to chancea small population due to chance Nonrandom mating: (AA mates AA, Aa) Nonrandom mating: (AA mates AA, Aa) Natural selectionNatural selection

One Example: Genetic drift in a small population

2.6 Speciation and mechanisms2.6 Speciation and mechanisms Speciation: splitting of one species into 2 Speciation: splitting of one species into 2

different species.different species.

Concept of species:Concept of species:• Biological Species: a species is a group of Biological Species: a species is a group of

organisms whose individual have the potential organisms whose individual have the potential to interbreed and produce fertile offspring. to interbreed and produce fertile offspring.

Reproductively isolated: donReproductively isolated: don ’’t produce fertile t produce fertile hybridshybrids

Natural conditions: artificial breeding doesnNatural conditions: artificial breeding doesn ’’t t count. For example, artificial insemination, count. For example, artificial insemination, keeping 2 species locked up together.keeping 2 species locked up together.

• Morphological species: members of the same Morphological species: members of the same species look similar to each other. Many species look similar to each other. Many examples of organisms that look similar but examples of organisms that look similar but cancan’’t produce fertile offspring.t produce fertile offspring.

• • No one species concept applies to all No one species concept applies to all

organismsorganisms Flickers

Genetic isolation mechanisms Genetic isolation mechanisms (reproductive barriers)(reproductive barriers)

Premating mechanismsPremating mechanisms• Habitat selection; temporal isolation; behavior or Habitat selection; temporal isolation; behavior or

mechanical or structure incompatibilitymechanical or structure incompatibility

Postmating mechanismsPostmating mechanisms• Genetic barrier such as hybrids are sterile; Genetic barrier such as hybrids are sterile; seed

abortion; hybrid inviability.

Mechanisms of speciationMechanisms of speciation

Several are well documented:Several are well documented:• Allopatric speciation (probably most Allopatric speciation (probably most

vertebrates)vertebrates) allopatric species occupy areas separated by allopatric species occupy areas separated by

time or space.time or space.

• Sympatric speciation (especially plants and Sympatric speciation (especially plants and insects)insects)

Sympatric species occupy the same place at the Sympatric species occupy the same place at the same timesame time

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

Allopatric speciation: Ring species

salamander

San Joaquin Valley, CA

Speciation via geographic isolation and divergence

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

About half of all flowering plants are polyploid: more About half of all flowering plants are polyploid: more than 2 copies of each gene. than 2 copies of each gene.

Polyploids are the result of failure of cell division Polyploids are the result of failure of cell division (mitosis or meiosis) to separate the chromosomes (mitosis or meiosis) to separate the chromosomes into 2 cells.into 2 cells.

2.4 Adaptations reflect trade-offs 2.4 Adaptations reflect trade-offs and constraintsand constraints

Adaptation: Individuals of a species Adaptation: Individuals of a species have certain characteristics that have certain characteristics that enable an organism to thrive in a enable an organism to thrive in a given environment.given environment.

Adaptations maintain or increase Adaptations maintain or increase fitness of an organism in a given fitness of an organism in a given environmental conditions.environmental conditions.

TradeoffTradeoff

Evolution is reflected in changes in Evolution is reflected in changes in gene frequencies and phenotypesgene frequencies and phenotypes

However, changes in gene However, changes in gene frequencies involve tradeoffsfrequencies involve tradeoffs

Giraffes do not graze well on grass Giraffes do not graze well on grass due to their long necksdue to their long necks

Snow leopards can hide in snowy Snow leopards can hide in snowy mountains, ordinary leopards can mountains, ordinary leopards can hide well in green trees.hide well in green trees.

ConstraintConstraint

There are many other There are many other factors that can influence factors that can influence species adaptation. species adaptation.

For example, response of For example, response of an organism to an an organism to an environmental gradient environmental gradient such as temperature.such as temperature.

All these factors influence All these factors influence species adaptation.species adaptation.

The EndThe End

Brief history of integration of Brief history of integration of Genetics into Ecological studiesGenetics into Ecological studies

Natural SelectionNatural Selection——Darwin (1859) The Origin of SpeciesDarwin (1859) The Origin of Species Particulate genetics & inheritanceParticulate genetics & inheritance——Gregor Mendel (1856-1864)Gregor Mendel (1856-1864) Mutations & chromosomesMutations & chromosomes——Hugo Devries & others (1901)--sources of variation Hugo Devries & others (1901)--sources of variation

in populations; rediscovery of Mendelin populations; rediscovery of Mendel’’s work s work ““The Modern SynthesisThe Modern Synthesis”” (Dobzhansky, Wright, Fisher, Haldane, Mayr, Simpson-- (Dobzhansky, Wright, Fisher, Haldane, Mayr, Simpson--

1930s & 1940s)1930s & 1940s)

• Integration Natural Selection & mutation; genetic drift; migrationIntegration Natural Selection & mutation; genetic drift; migration

• Appreciation of genetic variation within populations in natureAppreciation of genetic variation within populations in nature DNA structure/importance elucidated by Watson & Crick (1953) double helix DNA structure/importance elucidated by Watson & Crick (1953) double helix

structure of DNA structure of DNA Molecular variationMolecular variation in natural populations (Harris; Lewontin & Hubby 1966)-- in natural populations (Harris; Lewontin & Hubby 1966)--

using starch gel electrophoresis using starch gel electrophoresis molecular biology. molecular biology. Synthesis of Ecology with Genetics --> Evolutionary Ecology (starting in 1970s)!Synthesis of Ecology with Genetics --> Evolutionary Ecology (starting in 1970s)!

The major factors affecting the organismsThe major factors affecting the organisms’’ survival in the system is Fitnesssurvival in the system is Fitness

Darwinian fitness: ability of an organism to Darwinian fitness: ability of an organism to survive and reproduce in its environment.survive and reproduce in its environment.

Adaptation is a characteristic or trait of an Adaptation is a characteristic or trait of an organism that increases its fitness relative to organism that increases its fitness relative to individuals that do not possess it. It is an individuals that do not possess it. It is an inherited characteristic that increases the ability inherited characteristic that increases the ability of an organism to survive and reproduce.of an organism to survive and reproduce.

Evolution by Natural SelectionEvolution by Natural Selection

The traits selected for by natural selection need to be inheritable The traits selected for by natural selection need to be inheritable so that the next generation after selection retains the changeso that the next generation after selection retains the change

Three types of selectionThree types of selection• DirectionalDirectional

See finchesSee finches• StabilizingStabilizing

Long necks in giraffesLong necks in giraffes• DisruptiveDisruptive

Sexual dimorphismSexual dimorphism

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

SummarySummary What is natural selection? What is natural selection? Different types of NSDifferent types of NS Gene and genetic variationGene and genetic variation EvolutionEvolution Hardy-Weinberg principleHardy-Weinberg principle Concept of species. Concept of species. Speciation and mechanismsSpeciation and mechanisms Adaptation and trade-offsAdaptation and trade-offs

What is a speciesWhat is a species Ecology is based on the idea that we can identify Ecology is based on the idea that we can identify

different groups of organisms within an ecosystemdifferent groups of organisms within an ecosystem These groups are generally called speciesThese groups are generally called species There are three specific means of defining a speciesThere are three specific means of defining a species

• Morphological species conceptMorphological species concept A species is defined as a morphologically consistent group of A species is defined as a morphologically consistent group of

organisms than can be distinguished from all other speciesorganisms than can be distinguished from all other species• Can fail. So called cryptic speciesCan fail. So called cryptic species

• Biological species conceptBiological species concept A group of populations whose individuals can interbreed and A group of populations whose individuals can interbreed and

produce fertile offspring and cannot interbreed with other speciesproduce fertile offspring and cannot interbreed with other species Reproductive isolationReproductive isolation

• Still fails. If you cannot tell the individuals apart morphologically, how Still fails. If you cannot tell the individuals apart morphologically, how can you tell if they are interbreeding or notcan you tell if they are interbreeding or not

• Also, some species can interbreed and produce viable offspringAlso, some species can interbreed and produce viable offspring Bontebok and Blesbok in South AfricaBontebok and Blesbok in South Africa

• Genetic species conceptGenetic species concept A group of populations whose individuals have a distinct genetic A group of populations whose individuals have a distinct genetic

makeup and who do not interbreed with others groups of makeup and who do not interbreed with others groups of populations for some reasonpopulations for some reason

• Bontebok and Blesbok are genetically distinct as well as being Bontebok and Blesbok are genetically distinct as well as being morphologically different. Do not naturally overlap in rangemorphologically different. Do not naturally overlap in range

Geographical isolatesGeographical isolates

Salamanders

Adaptations of Honeycreepers on the island of Hawaii

RecapRecap

WhatWhat’’s Nature selection? 2 s Nature selection? 2 assumptions? assumptions?

Three types of natural selectionThree types of natural selection Concept in genetics: gene, Concept in genetics: gene,

chromosome, DNA, allele, locus, chromosome, DNA, allele, locus, genotype, phenotype, dominance, genotype, phenotype, dominance, incomplete dominance etcincomplete dominance etc