Exam 1 18-20

Barriers to a systematized theory of evolution?

Time, evolution is slow

Ability to spend time observing/comparing species from multiple locations

What did Lyell and Hutton contribute to evolution

Hutton and Lyell proposed gradual changes over a long time led to geological features on earth

Provides time necessary for evolution

Similar to mechanisms of evolution

What did Lamarck contribute to evolution

Proposed idea that changes in an organisms life could be inherited

Important step for Darwin and Wallace

What did Wallace and Darwin contribute to evolution

TRaveled on expeditions

Suggested a fram work for idea of evolution by natural selection

Darwin published first, more detailed

Whats the definition of NAtural Selection

Pop of organisms show variation of a trait

Certain forms of trait lead organisms to survive and reproduce better

That form of trait is better represented in next generation

Fitness definition

Ability of an organism to survive and reproduce better based on traits

Variation in Evolution definition

Any difference between organisms which have a genetic basis

All variations originally arise from mutations

What is Adaptation?

A heritable trait that helps an organism BETTER survive and reproduce in it’s environment

Physical, behavioral, etc.

What is Convergent evolution

Similar phenotypes occur in distantly related lineages due to similar selective pressure

Divergent evolution

Lineages become increasingly different from each other as a result of different selective pressures

Human,Bat, whale, and cat arms all contain the same bones but look different and erve different purposes

Ways to study evolution

Fossils, Anatomy, Biogeography, and MOLecular methods

How are fossils used to study evolution

Show change in lineages over time

Show extinct organisms are distinct from ones alive today

How is Anatomy and embryology used to study evolution?

Anatomy allows us to compare structural similarities and differences between organisms

Embryology can also be used to compare the relatedness of organisms

Biogeography

Geographic distribution of organisms on the planet follows patterns that we can explain best by evolution in conjunction with tectonic plate movement over geological time

Molecular evolution

Changes in the genetic code (mutations) accumulate the more distantly related organisms become

Studying molecular evolution also provides insight into some of the mechanisms of evolution we will discuss later

Common evolutionary misconceptions

Evolution is just a theory

Individuals evolve

Evolution explains the origin of life

Organisms evolve on purpose

What are the ecological levels from least to most broad

Individual→Population→Community→Ecosystem

Definition of an Individual in Ecology

A single example member of the species, such as a single zebra

Definition of Population in Ecology

Many individuals of the same species living in the same place

Definition of a community

Multiple different populations of species living in the same place

Definition of ecosystem

A community living in conjunction with its abiotic environment, such as rocks, water, etc.

What is a species

A group able to breed, and produce fertile, viable offspring.

Hybrids

Forced reproduction between organisms such as a donkey(2n=62) and horse(2n=62)
Mule

Gene flow

Movement of alleles within and between populations

Animals move through territory or leave natal group

Sessile organisms typically have motile gametes/seeds

New gene flow

Increases genetic diversity

Long term geneflow

Reduces genetic diversity acroiss both populations

BGoth pops become homogenous

Allele freque3cy normalizes across both

No mutation accumulation

Speciation

Formation of two separate species from one original parent population

Allopatric speciation

Allo: other
Patris: homeland

Physical separation of the two new populations from the parent population, then subsequent speciation

Sympatric Speciation

Sym: Same
Patris:homeland

Speciation occurs when both new populations inhabit the same geographical range as the parent species

Dispersal

Allopatric speciation

Whenb a few members of a population move to a new area

Vicariance

Allopatric speciation

When geographical barriers physically divides the population
Reduces gene flow

Allopatric speciation results in what kind of adaptations

Divergent adaptations due to environmental pressures
Different mutations

Change in allele frequency

Adaptive Radiation

Relatively rapid evolution of many species from a single ancestor.

Results from new resource/habitat

Darwin’s finches and Allopatric specoation

Natural selection for specific food resources lead to evolution of bill adaptation

What causes Sympatric Speciation

Reproductive isolation

Caused by:Temporal;, behavioral, or habitat isolation, or polyploidy

Temporal

Variation in time of day or seasonality of mating (Plants/animals)

Behavioral

Different mating cues (animals)

Habitat

Individuals specialize within their environment

(typically leads to behavioral isolation)

Polyploidy

Tetraploidy

Reproductive Isolation

Prevents individuals from different species from interbreeding or, if they do interbreed, resultant offspring are nonviable or infertile.

Prevents gene flow between different species

Prezygotic barrier

Prevents mating from occurring or prevents fertilization from occuring

Postzygotic barrier

Zygote does not develop and dies or

Offspring is sterile

Prezygotic Barriers Examples

Temporal: reproduce at different times of year

Habitat: Individuals close but different habitats

Behavior: mating cues are different

Mechanical: Incompatible reproductive structures/incompatible gametes

Reconnection of Species

Recently differentiated species can interact with each other, “Hybrid Zone”

What do less fit hybrids do?

They reinforce speciation

Species will continue on different trajectories

As speciation progresses, fewer hybriuds are formed

eventually there will be no hybrids

Fusion of two species into one

When hybrid barriers weaken, species can fuse into one

Stabilization

When the two species remain seperate but interbreed and produce hybrids. Hybrid species may differentiate into a third species

Gradual speciation

Slow divergence of species over time

Small intermediate steps of speciation

Punctuated Equilibrium

NEw species diverge quickly from parents species and remain unchanged for long periods of time

Primary driver of speciation rate

Environmental conditions

Gene

Unit of DNA, transmits genetic information. Codes for a specific protein.

Locus

Each gene has a specific location on the chromosome.

Phenotype

Obser5vable trait of individual. Determined by genotype

Alleles

Different versions of a gene

Genotype

Specific alleles present in an individual

Phenotype

Observable trait of individual. Determined by genotype

Diploid (2n)

2 copies of each chromosome

Somatic body cerlls

Mitosis produces two diploid cells from one diploid parent cell

Haploid (n)

1 copy of eazch chromosome

Gametes (eggs and sperm)

Meiosis produces four haploid cells from one diploid parent cell

Microevolution

Small scale changes in allele frequency of a population

Changes in a genepool

From one generation to the next

Results in phenotypic change

Eventually leads to genus-level speciation

Macroevolution

Large-scale changes in allele frequency of a population

Extends over a long period of time

Gives rise to new species

Extends beyond the genus level

Allele frequency

Rate at which a specific allele occurs in a population

Can change in response to selective pressures, where one allele is more advantageous than another

Fixed allele

Only one version of an allele in a population

Genotype frequency

Rate at which a specific genotype occurs in a population

Genotype frequencies change as allele frequencies change

Population Genetics

Measure the effect of natural selection on allele and genotype frequencies in a population

Change in a populations allele frequency is evolution

Genepool

Is the sum of all alleles present within a population

Genetic drift

When allele frequencies change rapidly with no apparent advantage

Characteristics of genetic drift

Due to random chance

Happens in small populations

Alleles can quickly become fixed due to genetic drift

Founder effect

Initiates change in allele frequency in an isolated population

Happens when organisms spread to a novel environment

Islands

Hardy Weinberg Equilibrium conditions

No gene flow

No natural selection

No mutation

Random mating

No genetic drift (infinitely large populations)

Formula for allele frequency

p+q=1

Genotype frequency

p²+2pq+q²=1

Genetic Drift

Change in allele frequency due to random chance\

Some individuals have more offspring than other individuals

Some individuals do not reproduce

Occurs in all populations

Has significant effect in small populations

Has less effect in large populations

Can lead to allele fixation

Only one allele present in population

Founder effect

Skewed representation of alleles in population

Some individuals leave parent population to inhabit new areas

Bottle neck event

An event that drastically reduces popultion size

Skewed representation of alleles in population

Only certain individuals survive the bottle neck event

Allele frequencies are based on alleles present in individuals that survive

Non-random mating

Not all individuals have an equal opportunity

Non random mating

Not all individuals have an equal opportunity to mate

Most species compete for mates

Mate choice: females prefer to mate with a male with specific traits

Sometimes also caused by geographic location

Few individuals in an area→less mate choice

Even within a large popln those closest to each other mate with each other

Gene flow

Flow of alleles in and ouj of a population due to migration

No immigration/emigration means no gene flow

Immigration/emigration is gene flow

Rate of gene flow affects allele frequency

Initial gene flow between populations increases the genetic variation within the receiving population

continual gene flow between populations leads to less genetic variation between those populations

Natural selection and beneficifial traits

Increases allele frequency in population

Natural selection and deleterious traits

Selects against deleterious traits, decreases frequency

Natural selection and alleles

Is selecting for phenotypes not alleles

Selects for individuals who contribute most to the gene pool (evolutionary fitness)

Relative fitness

Measure of an individuals fitness relative to the fitness of others in the population

Individuals with high relative fitness will have higher contributions to gene pool

Effects of natural selection/adaptive evolution

Stabilizing selection

directional selection

disruptive selection

frequency dependent selection

Sexual selection

Stabilizing selection

Selective pressure for average phenotype(greater relative fitness)

Selective pressure against extreme phenotypes(less relative fitness)

Genetic variance decreases

Directional selection

Selective pressure for one extreme phenotype(greater relative fitness)

Selective pressure against the other extreme and avergae

Populations genetic variance shifts to new phenotype

Diversifying selection

Selective pressure for both extreme ohenotypes

selective pressure against average phenotype

genetic variance in population will increase

Positive frequency dependent selection

Select sfor common phenotypes

Relative fitness increases when phenotype is common

Relative fitness decreases when phenotype is rare

decreases genetic variance

Rare phenotypes (negative frequency-dependent)

Relative fitness decreases when phenotype is common

Relative fitness increases when phenotype is rare

increases genetic variance

Sexual selection

Selection of phenotype that is gendered

Sexual dimorphism

is when males and females of a species exhibit phenotype differences beyond reproductive organs

Occurs when males’ ability to mate is more variable than females'

• Bigger/stronger males can fight off other males

• Prettier/showy males are more attractive to females

Variation in male reproductive success creates strong sexual selection for:

• Males to be bigger/stronger, or prettier/showy

• Females to choose to mate with males that are bigger/stronger, or prettier/showy

Handicap principle/good gene hypothesis

Phenotype is such a disadvantage that only the fittest males can survive with it

Extravagant male traits may be indicator of their superior genetic quality

• Honest signal to females

Females mate with these males so their offspring inherit better genes which leads to increased fitness

• Females choosing to mate with these males further reinforce the selective pressure

Taxonomy

International classification system used to name organisms in a hierarchical manner

• More→less inclusive

• Less→more related

• Each taxonomic group is called a taxon

• Genus species← right form

Systematics

Classifies organisms based on their evolutionary relationships

• Fossil data

• homolgous structures

• biomolecular data

• DNA

Phylogeny

Evolutionary history of organisms and their relationships to other organisms

Phylogenetic tree

Uses systematics and phylogeny to reflect evolutionary relationships and history

Hypotheses of the past

rooted, phylogeny term

Single common ancestor

Brnach point

Single lineage splitting into two

Bars

Evolution of novel trait

Basal taxon

Unbranched lineage evolved from the common ancestor,

the outgroup

Sister taxa

Two lineages stemming from same branch point

Polytomy

Branch with three or more lineages, undetermined relationships