LAB:Variation in a Species

• What is the purpose of Part 1?• (Measuring Pumpkin seeds)

• There is variation in size in Pumpkin plants. Variation can be measured.

LAB:Variation in a Species

• What is the purpose of Part 2?• (Calculate how long it takes pumpkin plants to take over

the Earth)

• There are reasons to explain why pumpkin plants have not ever taken over the Earth

LAB:Variation in a Species

• What is the purpose of Part 3?• (Effect of predators on sweet cute Bonitos)

• There are reasons to explain why the population of bonitos on one island look different from bonitos on another island

What is a species?

• A group of living things that

• are similar,

• and can breed together in nature

• to produce fertile offspring.

What is a population?

• A group of living things that

• belong to the same species,

• live in the same area,

• and can reproduce together.

What is a gene pool?

• The total collection of genes in a population at any one time.

Hardy & Weinberg

• What is allele frequency?

• 1908: Hardy and Weinberg invented the term “allele frequency” to describe the percentage of dominant and recessive alleles found in a populaton.

Hardy & Weinberg

• How is allele frequency measured?

• Example: a lizard population might have the following allele frequency for the alleles F and f:

• FF = 0.64 (64%)• Ff = 0.32 (32%)• ff = 0.04 (4%)

Hardy & Weinberg

• What is genetic equilibrium?

• 1908: Hardy and Weinberg invented the term “genetic equilibrium” to describe a population in which the frequency of alleles stays the same from one generation to the next.

Hardy & Weinberg• How was genetic equilibrium measured?

• Hardy-Weinberg equations:• p2 + 2pq +q2 = 1• p + q = 1

Hardy & Weinberg• Hardy-Weinberg Equations

• Where p2 is the frequency of homozygous dominant individuals

• Where 2pq is the frequency of heterozygous individuals

• Where q2 is the frequency of homozygous recessive individuals

Hardy & Weinberg• What causes genetic equilibrium?• There must be…….

• A large population

• Members mating at random

• No mutation• No migration• No natural selection

Hardy & Weinberg• What can cause allele frequency to change?

• Migration (also called gene flow)

• Mutation

• Mate selection (non-random mating)

• Predators, disease, famine, drought, storms, accidents.

Observing Variation

• (1) Variation exists in living populations.

• (2) Some variations are helpful and increase life span.

• (3) Some variations are harmful and decrease life span.

Observing Variation

• (4) A population may become physically separated, so two groups form.

• (5) As mutations and meiosis occur, new variations will appear.

• (6) Some offspring will survive better than others.

Observing Variation

• (7) Offspring that survive in one area may not survive in another area.

• (8) Over time, more variations will accumulate in the two populations.

• (9) The two populations will become different because different variations occur in the two groups.

Observing Variation

• (10) Individuals that die out do not get to reproduce.

• (12) Sometimes, a new species has formed.

• (11) In some cases, the two groups become so different from each other that they can no longer interbreed.

What is this Process?

• Evolution of species

• A set of natural processes that causes change in a population of living things over time.

• Biological evolution, simply put, is descent with modification.

Why was this little sticker so controversial?

Source: http://www.swarthmore.edu/NatSci/cpurrin1/textbookdisclaimers/CobbDisclaimer.jpg

Understanding Evolution

• Scientists study natural processes and look for natural explanations.

• I will introduce you to some of the evidence that leads biologists to view evolution as the great unifying theory of the field.

• Science cannot answer every question.

• What if you disagree with photosynthesis?

Evolution by Natural Selection

• Variation exists in every population.

• Natural selection (predators, disease, drought, cold, famine, flood, heat…..) causes some individuals to survive while others do not.

• Sources of inherited variation: meiosis, crossing over, mutation.

• Allele frequency change is called evolution. Sometimes it causes speciation.

Charles Darwin• Age 25: set sail on 5 year voyage on HMS

Beagle as “naturalist”.

A reconstruction of the HMS Beagle sailing off Patagonia.

Darwin’s Voyage of Discovery

The Voyage of the Beagle

Cape Verde and Galapagos Archipelegos

Galapagos Islands and South American Mainland

Intra-Galapagos Variability:Darwin’s Finches

Darwin saw patterns among a diverse, extensive array of fossils & specimens(worked on it for a couple decades!)

Charles Darwin observed animals and plants in the Caribbean, South America, the Galapagos, Hawaii, Indonesia, Africa and Europe.

• He took massive notes in several notebooks.• He wrote three books about his experiences.

Common AncestorThe central idea of biological evolution is that all life on Earth shares a common ancestor, just as you and your cousins share a common grandmother.

Darwin’s Notebook

Darwin’s Ideas Did Not Develop in a Vacuum

Contributor’s to Darwin’s thinking included:

Charles Lyell – uniformitarianism.

1797-1875

Georges Cuvier – species extinction.

1769-1832

Darwin’s Ideas Did Not Develop in a Vacuum

Contributor’s to Darwin’s thinking included:

Thomas Malthus – struggle for existence.

1766-1834

Jean Baptiste de Lamarck – evolution by acquired characteristics.

1744-1829

Jean Baptiste de Lamarck

• Animals face a need to change.

• Animals make themselves change

• Animals pass on the changes to offspring.

• “Inheritance of Acquired Characteristics”

Alfred Russel Wallace Independently Drew the Same Conclusions as Darwin

Papers from Wallace and Darwin were jointly presented (with little impact) to the Linnaean Society in 1858.

Evolution by Natural Selection

• Variation exists in a population. (Darwin did not know how the variation was passed…genetics was not yet understood)

• Some organisms survive and pass on genes…some do not.

• Causes of this evolution: migration, “heredity”, mate selection, predators, disease, famine, drought,

Lamarck and Wallace: How would they explain these observations?

• In 1960, a pesticide was sprayed at Tybee Island, GA, killing 97% of all mosquitoes.

• In 1979, the same pesticide killed less than 30% of all the mosquitoes.

• Lamarck: Wallace:

Darwin’s Observations and Inferences

Observation 1: Left unchecked, the number of organisms of each species will increase exponentially, generation to generation.

Observation 2: In nature, populations tend to remain stable in size.

Inference 1: Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals, with only a fraction of offspring surviving in each generation.

Observation 3: Environmental resources are limited.

Darwin’s Observations and Inferences

Observation 4: Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike.

Observation 5: Much of this variation between individuals is heritable.

Inference 2: Survival in the struggle for existence is not random, but depends in part on the heritable characteristics of individuals. Individuals who inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals.

Darwin’s Observations and Inferences

Inference 3: The unequal ability of individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations (natural selection).

Taken together, these three inferences are a statement of Darwin’s Theory of Evolution.

Darwin’s Observations and Inferences

Genetics and the Modern Synthesis

A major problem in Darwin’s theory was the lack of a mechanism to explain natural selection.

How could favorable variations be transmitted to later generations?

With the rediscovery of Mendel’s work and its vast extension in the first half of the 20th century, the missing link in evolutionary theory was forged.

Darwinian theory supported by genetics is known as the modern synthesis.

The Modern Synthesis1932-1953

1) Mutation and segregation result in large variability within populations

2) Individuals pass alleles to offspring

3) Differential reproductive success

4) Adaptation increases allelic fitness

How can allele frequency change?

Mutation

• Migration

• Meiosis and crossing over

• Genetic drift (luck)

• Natural Selection (predators, disease, famine, drought)

• Non-random mating (sexual selection)

How can evolution occur?

Mutation

• Migration

• Meiosis and crossing over

• Genetic drift (luck)

• Natural Selection (predators, disease, famine, drought)

• Non-random mating (sexual selection)

Evidence that evolution takes place

• Homologous or vestigial structures

• Biogeography

• Homologous DNA and proteins

• Fossil evidence

• Evolution observed right now

Why use the same skeletal plan for these very different appendages?

Homologous skeletal structure

Homologous Structures

Bees, ants and wasps have stingers which are modified ovipositors…which explains why only females can sting!

Vestigial whale pelvis bones

Vestigial anthers and pollen: Dandelions are asexual

Evidence of Evolution –Conservation and Diversification at the Molecular Level

Why does the degree of relationship of genes match their degree of relationship established by other methods?

Why should different organism possess related genes?

Embryo Homology

Evidence for Evolution - Comparative Embryology

Why do embryos of different animals pass through a similar developmental stage?

Recent discoveries of the conservation of molecular mechanisms of development are even more compelling.

Plant embryo homology

Evidence for Evolution – Evolution Observed

Evolution of pesticide resistance in response to selection.

Explain how this is perceived as an example of evolution.

Evidence for Evolution – Evolution Observed

Evolution of drug-resistance in HIV.Interpret this example of evolution.

Bear evolution based on homologous DNA genes

Whale and dolphin evolution based on DNA homology

Evolution: Changes in allele frequency over time

Phylum Annelida segmented worm evolution based on fossil and DNA homology

Evolution of Turtles, with massive fossil evidence

Biogeography

Hawaiian Monk Seals

Common Ancestor

Evolution: Changes in allele frequency over time

Whale evolution

Hardy-Weinberg genetic equilibrium

• Allele frequency will not change as long as:• There is no migration (gene flow)• There is no mutation• There is random mating• There is no natural selection• The population is large, so there is no

genetic drift

Genetic Drift: The Founder Effect• A few individuals are separated from the

original population.• All the descendants resemble the founders,

even if those traits are not best for the environment.

• EXAMPLE: island tortoises

Genetic Drift: Bottleneck Effect

• A large population declines rapidly.• The survivors reproduce and the population

goes up in number, but the new population resembles the survivors.

• The genes of the new population are often more uniform, with less variation

• EXAMPLE: cheetahs

Natural Selection

• Stabilizing Selection: natural selection removes organisms at the extremes of a population….like Goldilocks.

Natural Selection

• Directional selection: natural selection removes organisms at one extreme and in the middle, favoring one extreme.

Natural Selection

• Disruptive selection: natural selection removes organisms with the average form of a trait, favoring both extremes.

How to form new SPECIES?

• Reproductive isolation is required.• Allopatric speciation:

– Geographic barrier divides the population (ocean, canyon, mountain)

• Sympatric speciation

– Organisms all live in same area, isolated by song, timing, mutation

Adaptive Radiation – process by which a single species evolves into several different forms that live in different ways

Songbirds from South America Honeycreepers from Hawaii

Convergent Evolution – process by which unrelated organisms independently evolve similarities when adapting to similar environments.

Nothing in biology makes sense except in the light of evolution. Theodosius Dobzhansky

Charles Darwin in later years