Review

All populations of species have within them genetic variation that results in qualitative and quantitative differences in phenotype

Environments cycle through periods of stasis and flux

Organisms best suited to compete for available resources produce the most viable offspring

What are the sources of variation?

Mutations in genes Recombination of alleles during

meiosis (crossing over) Orientation of homologous

chromosomes during metaphase I

Fertilization (one sperm and egg out of many variations)

What causes the change of variation (allele frequency) within a population?

MutationsGene flow (immigration)Nonrandom matingGenetic drift (founder and bottleneck effects)

Selection (artificial and natural)

Mom, Dad…There’s something you need to know…

I’m a MAMMAL!

The Origin of Species

“That mystery of mysteries…”

Darwin never actually tackled how new species arose…Darwin never actually tackled how new species arose…

Both in space and time, we seem to be brought

somewhat near to that great fact—that mystery of mysteries—

the first appearance of new beings on this Earth.

So…what is a species?

Biological species concept population whose members can interbreed &

produce viable, fertile offspring reproductively compatible

Western MeadowlarkEastern Meadowlark

Distinct species:songs & behaviors are different enough to prevent interbreeding

Distinct species:songs & behaviors are different enough to prevent interbreeding

How and why do new species originate?

Species are created by a series of evolutionary processes populations become isolated

geographically isolated reproductively isolated

isolated populations evolve independently

Isolation allopatric

geographic separation sympatric

still live in same area

Speciation

The process by which a new species is formed from a related preexisting species

The development of a new branch on the tree of life

The formation of a new and isolated gene pool

Begin class by working on speciation vocabulary

assignment for 10 minutes

Please do so QUIETLY

Hardy-Weinberg Equilibrium

Assume a population of monkeys living on an island is in Hardy-Weinberg equilibrium No mutations, large population size, no gene flow, no

genetic drift, no natural selection.This means that the allele frequencies of the gene

pool does not change from one generation to the next.1=p2 +2pq + q2

If 25% of the monkeys exhibit the dominant trait of black fur, and there are 200 monkeys in the population, how many of have a heterozygous genotype?

Factors the affect variation within a population (Changes allele frequency in a gene pool)

Reduces Variation

Increases Variation

MutationsImmigrationIndependent

AssortmentBottleneck EffectNatural SelectionRandom FertilizationEmmigrationNon-random MatingCrossing Over

(meiosis)

In your notes, fill in the t-chart above with the terms listed to the

right

Isolation Leads to Speciation

Types of Isolating Mechanisms

Pre-zygotic Isolating Mechanisms

Ecological Geographical Mechanical Temporal Behavioral Gametic

Post-zygotic Isolating Mechanisms Reduced Hybrid

Viability Reduced Hybrid

Fertility Hybrid

Breakdown

PRE-reproduction barriersObstacle to mating or to fertilization if mating

occurs

behavioral isolation

geographic isolation ecological isolation temporal isolation

mechanical isolation gametic isolation

Geographic isolation

Species occur in different areas physical barrier

Ex. canyon, river, forest, desert, ocean, mountain, etc.

allopatric speciation “other country”

Harris’s antelope squirrel inhabits the canyon’s south rim (L). Just a few miles away on the north rim (R) lives the closely related white-tailed antelope squirrel

Harris’s antelope squirrel inhabits the canyon’s south rim (L). Just a few miles away on the north rim (R) lives the closely related white-tailed antelope squirrel

Ammospermophilus spp

Geographical Isolation

Ecological isolation

Species occur in same region, but utilize habitats differently so they rarely encounter each other Sympatric speciation (same

country)

2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial

2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial

Ecological Isolation

The Anopheles genus consists of six mosquito species

The species are virtually indistinguishable morphologically, but are isolated reproductively

They breed in different habitats.

Some breed in brackish water, others in running fresh water, and still others in stagnant fresh water.

Temporal isolation

Species that breed during different times of day, different seasons, or different years cannot mix gametes reproductive isolation sympatric speciation

Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

Temporal Isolation

Behavioral isolation

Unique behavioral patterns & rituals isolate species identifies members of species attract mates of same species �

courtship rituals, mating calls, etc.

Blue footed boobies mate only after a courtship display unique to their species

Blue footed boobies mate only after a courtship display unique to their species

firefly courtship displaysfirefly courtship displays

courtship display of Gray-Crowned Cranes, Kenya

courtship display of Gray-Crowned Cranes, Kenya

courtship songs of sympatricspecies of lacewings

courtship songs of sympatricspecies of lacewings

Recognizing your own species

Mechanical isolation

Morphological differences can prevent successful mating

Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. These 2 species of monkey flower differ greatly in shape & color, therefore cross-pollination does not happen.

Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. These 2 species of monkey flower differ greatly in shape & color, therefore cross-pollination does not happen.

Plants

Mechanical isolation

For many insects, male & female sex organs of closely related species do

not fit together, preventing sperm transfer

lack of “fit” between sexual organs: hard to imagine for us… but a big issue for insects with different shaped genitals!

Damsel fly penises

Animals

Mechanical isolation

Bush babies, a group of small arboreal primates, are divided into several species based on mechanical isolation.

Each species has distinctly shaped genitalia that, like locks and keys, only fit with the genitalia of its own species.

Gametic isolation

Sperm of one species may not be able to fertilize eggs of another species mechanisms

biochemical barrier so sperm cannot penetrate egg receptor recognition: lock & key between egg & sperm

chemical incompatibility sperm cannot survive in female reproductive tract

POST-reproduction barriers

Prevent hybrid offspring from developing into a viable, fertile adult

reduced hybrid viability reduced hybrid fertility hybrid breakdown

zebroid

Reduced hybrid viability

Genes of different parent species may interact & impair the hybrid’s development

Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.

Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.

Mules are vigorous, but sterile

Reduced hybrid fertility

Even if hybrids are vigorous they may be sterile chromosomes of parents may differ in

number or structure & meiosis in hybrids may fail to produce normal gametes

Donkeys have 62 chromosomes(31 pairs)

Horses have 64 chromosomes(32 pairs) Mules have 63 chromosomes!

Reduced Hybrid Fertility

The Liger-massive, but sterile

Hybrid breakdown

Hybrids may be fertile & viable in first generation, but when they mate offspring are feeble or sterile

In some strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile.On path to separate species.

In some strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile.On path to separate species.

Isolation Can Lead to Speciation

One Gene Pool

Isolation

Independent Adaptation

Many Generations

Removal of Barrier

Design an Experiment!

Work with a partner, record your ideas on a separate sheet of paper that will be turned in.

Choose a laboratory organism… Fruit fly, convict cichlid, pea plant

Develop an experiment that you think could result in the formation of two distinct species from the original. Describe your procedure in as much detail as you can, as if you

were going to perform this experiment.

Hint: How will you know when two species have formed?

Trends in Evolution

Adaptive RadiationDivergent EvolutionConvergent EvolutionGradualismPunctuated EquilibriumPolyploidyTransient PolymorphismBalanced Polymorphism

Divergent Evolution

Speciation often happens repeatedly, to form a group of species from one ancestral lineage.

Often these species evolve in different ways due to random genetic variation and varying selective pressures

This is known as divergence

Adaptive Radiation

Rapid and repeated divergenceOften occurs when a multiple varying niches

are available

Convergent Evolution

Organisms sometimes adapt similar solutions to physiological problems presented by similar selective pressures

Unrelated species show striking similarities

Convergent Evolution of Marsupial and Placental Mammals

Niles EldredgeCurator

American Museum of Natural History

Rate of Speciation

Current debate:Does speciation happen gradually or rapidly Gradualism

Charles Darwin Charles Lyell

Punctuated equilibrium Stephen Jay Gould Niles Eldredge

Gradualism

Gradual divergence over long spans of time assume that big changes

occur as the accumulation of many small ones

Punctuated Equilibrium

Rate of speciation is not constant rapid bursts of change long periods of little or no

change species undergo rapid

change when they 1st bud from parent population

Visualizing Evolution

The Cambrian Explosion:Evidence of Punctuated

Equilibrium

The Tale of Two Snails

Environment Changes

Snails in new environment adapt

Two different population

Environment keeps changing

Survival of the Fittest

Everything’s back to normal (kind of)

The Fossil Record

Polyploidy

Errors during meiotic cell division result in extra sets of chromosomes, a condition called polyploidy

30-70% of flowering plants thought to be polyploid

Polyploid types are labeled according to the number of chromosome sets in the nucleus:

triploid (three sets; 3x), for example the phylum Tardigrada tetraploid (four sets; 4x), for example Salmonidae fish Pentaploid (five sets; 5x) hexaploid (six sets; 6x), for example wheat, kiwifruit octaploid (eight sets; 8x), for example Acipenser (genus of sturgeon

fish) decaploid (ten sets; 10x), for example certain strawberries dodecaploid (twelve sets; 12x), for example the plant Celosia argentea

and the amphibian Xenopus ruwenzoriensis

Speciation via polyploidy

A diploid cell undergoes failed meiosis, producing diploid gametes, which self-fertilize to produce a tetraploid zygote.

Polymorphisms: Traits with multiple, distinct phenotypes (morphs)

Transient Polymorphisms

One morph or allele with gradually replace the other as generations pass because it confers a reproductive advantage

Pepper Moth is the classic example of this.

Pepper Moths

Balanced Polymorphism

The various morphs are maintained with a population throughout multiple generations

Sickle Cell Anemia is the most thoroughly researched example of this.

Evolution is not goal-oriented

An evolutionary trend does not mean that evolution is goal-oriented.

Surviving species do not represent the peak of perfection. There is compromise & random chance involved as well

Is this also true for humans as well?