Selection and the Blond Beach Mouse Selection and the Blond Beach Mouse by Joan Sharp Department of...

Selection and the Selection and the Blond Beach MouseBlond Beach Mouse

byJoan SharpDepartment of Biological SciencesSimon Fraser University, BC, Canada

Introducing Dr. Hopi Hoekstra

Dr. Hoekstra is Professor of Zoology and Curator of Mammals at Harvard University. She studies the oldfield deer mouse, Peromyscus polionotus, to understand the evolution of its cryptic coloration and behavior.

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Part I: The Adaptive Value of Cryptic Coloration

The Oldfield Deer Mouse

Peromyscus polionotus3

The Oldfield Deer Mouse

• Oldfield deer mice (Peromyscus polionotus) live in abandoned agricultural fields throughout the SE United States.

• They live in loosely packed sandy or clay soils, where they can dig their burrows.

• Mainland oldfield deer mice have a dark brown dorsal coat, a light grey belly, and a striped tail.

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The Beach Mouse

The Alabama beach mousePeromyscus polionotus subspecies ammobates

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The Beach Mouse

• Beach mouse populations of Peromyscus polionotus have colonized sand dune and barrier island habitats, where they live on brilliant white sand with sparse vegetation.

• Beach mice look very different from their mainland cousins, with a lightly colored dorsal coat and no pigment on their face, belly, and tail.

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Eight Subspecies of Beach Mice

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Eight subspecies of beach mice live on sand dunes on beaches and barrier islands that formed ~6000 years ago along the Gulf Coast of Alabama and Northern Florida and the Atlantic Coast of Florida.

Discuss in your small groups:

1.What random process was necessary for beach mice to evolve from dark mainland mice?

2.What non-random process was necessary for beach mice to evolve from dark mainland mice?

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Evolution of Blond Beach Mice

Mutation:A random mutation in one or more of the genes affecting coat coloration caused light coloration in the coat of the mutant mouse.

Natural selection: Beach mice with mutations that produced light coat color had higher survival and reproductive success than dark beach mice.

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Understanding Natural Selection

• Biologists ask ultimate questions about why natural selection has favored a particular trait.

• Ultimate explanations address the adaptive value of the trait, exploring how the trait increases evolutionary fitness in a specific environment.

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Understanding Natural Selection

• Biologists also ask proximate questions about how a particular trait is expressed.

• Proximate explanations address the mechanisms that produce the trait, including its genetic, developmental, or physiological basis.

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Definitions

• Evolutionary fitness measures the relative ability of an individual to produce viable, fertile offspring, relative to other individuals in the population.

• An adaptation increases an individual’s evolutionary fitness relative to other individuals in the population.

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CQ#1: Japanese cranes breed in spring and early summer. Choose the ultimate explanation:

A. Breeding is most likely to be successful in spring and early summer.

B. Hormonal changes bring about breeding behaviors.

C. Breeding is triggered by the effect of increased day length on the birds’ photoreceptors.

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B. Hormonal changes bring about breeding behaviors.

C. Breeding is triggered by the effect of increased day length on the birds’ photoreceptors.

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CQ#1: Japanese cranes breed in spring and early summer. Choose the ultimate explanation:


B. Increasing day length triggers the release of breeding hormones.

C. Ample food is available for chicks at this time.

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CQ#2: Japanese cranes breed in spring and early summer. Choose the proximate explanation:


B. Increasing day length triggers the release of breeding hormones.

C. Ample food is available for chicks at this time.

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CQ#2: Japanese cranes breed in spring and early summer. Choose the proximate explanation:

Ultimate Questions

Hoekstra’s team asked two ultimate questions about natural selection for coloration in oldfield deer mice:

1.Why is blond fur adaptive in beach mice?

2.Why is dark fur adaptive in mainland mice?

Oldfield deer mice have many visual predators, including hawks, owls, and coyotes.

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Hypothesis 1:

Blond beach mice are camouflaged and less vulnerable to predation in a beach habitat.

Hypothesis 2:

Dark mainland mice are camouflaged and less vulnerable to predation in a mainland grassy field habitat.

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Two Complementary Hypotheses

Work in your small groups to plan an experiment to test these hypotheses, marking sure that you include the following:

•Describe your experimental setup.

•Independent variable: What will you vary in your experiment?

•Dependent variable: What will you measure in your experiment?

•What variables will you control or standardize?

•How will you provide replication?

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Experimental Design Can Be Tricky!

If you plan an experiment to test predation risk on blond and dark mice in natural beach and field habitats, consider:

•The color of mice in a particular habitat may not vary much.

•It can be hard (or impossible) to follow an individual mouse and determine its fate.

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Experimental Design Can Be Tricky!

If you plan an experiment to test predation risk on blond and dark mice in enclosures that mimic natural beach and field habitats, consider:

•It’s hard to provide a full set of natural predators in an enclosure.

•Blond and dark mice may vary in other ways, such as odor, activity level, and behavior. (Do mice try to hide? Escape?)

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The Experiment

• Dr. Hoekstra and her colleagues made models of oldfield deer mice with beach and mainland coloration to assess the adaptive value of camouflaged coloration in nature.

• They made 250 soft Plasticine models of crouching Peromyscus polionotus.– Half were painted to look like beach mice.– Half were painted to look like mainland mice.

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Plasticine Mice

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The Experiment

• The models were set out in 8 linear transects where Peromyscus polionotus lives. – 4 transects were in beach habitats– 4 transects were in mainland habitats

• 14 light and 14 dark model mice were randomly set out on open patches 10 m apart along each transect.

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The Experiment

• Model mice were checked every 24 hours and attacked models were replaced with identical models.

• Predatory attacks were scored by the presence of bite marks, bill marks, dragging of models, or other “injuries.”

• The proportion of attacked model mice that matched or mismatched their habitat were calculated (relative to the total number of mice attacked).

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Work in your small groups to identify the following features of Dr. Hoekstra’s experiment:

1.What is the independent variable?

2.What is the dependent variable?

3.What variable(s) are controlled or standardized?

4.How is replication provided?

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What results would you expect if the data support Hypothesis 1?

Hypothesis 1: Blond beach mice are camouflaged and less vulnerable to predation in a beach habitat.

Make a prediction!

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Pro

po

rtio

n o

f at

tack

s

Dark models Light models

Predict the proportion of attacks on dark and light models in a beach habitat

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What results would you expect if the data support Hypothesis 2?

Hypothesis 2: Dark mainland mice are camouflaged and less vulnerable to predation in a mainland grassy field habitat.

Make a prediction!

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Pro

po

rtio

n o

f at

tack

s

Dark models Light models

Predict the proportion of attacks on dark and light models in a field habitat

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The Results

31Predation on dark and light models in beach or field habitats

CQ#3: What do these results show?

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Predation on dark and light models in beach or mainland habitats.

A. Predation on dark and light models is similar in both habitats.

B. Camouflaged models suffer no predation in both habitats.C. Predation on camouflaged models is reduced relative to

non-camouflaged models in both habitats.

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CQ#3: What do these results show?

A. Predation on dark and light models is similar in both habitats.

B. Camouflaged models suffer no predation in both habitats.C. Predation on camouflaged models is reduced relative

to non-camouflaged models in both habitats.

Predation on dark and light models in beach or mainland habitats.

Work in your small groups to discuss whether these results allow you to support or reject the two hypotheses.

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Hypothesis 1:

Blond beach mice are camouflaged and less vulnerable to predation in a beach habitat.

Hypothesis 2:

Dark mainland mice are camouflaged and less vulnerable to predation in a mainland grassy field habitat.

Dr. Hoekstra and her colleagues have answered the ultimate question about the evolution of blond coloration in beach mice.

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Why is blond color adaptive?

• Blond coloration is adaptive in beach populations of Peromyscus polionotus because blond mice suffer reduced predation by visual predators.

• With increased survival, blond beach mice are more likely to reproduce successfully and have higher evolutionary fitness than dark beach mice.

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Proximate Questions

Hoekstra’s team asked two proximate questions about blond coloration in beach mice:

1.What are the genes that affect coat color in mice?

2.What mutations in these genes produce blond coat color in beach mice?

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Part II (Detailed Version)

The Genes and Alleles Affecting Coat Color in Mice

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How is fur coloration determined?

• Mammals are unique in having hair or fur.• Each hair grows from a hair follicle, and

melanocytes at the base of each follicle produce pigments that are deposited in the growing hair.

• In mammals, variation in pigmentation is determined by the distribution and relative amounts of two pigments: pheomelanin and eumelanin.

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Mammalian Pigments

Eumelanin pigments produce dark colored hairs that vary from brown to black, depending on the distribution and number of pigment molecules in each hair.

Pheomelanin pigments produce light colored hairs that vary from blond to red.

A hair can have a banded pattern if it switches between these pigments as it grows.

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Genes Affecting Hair Color

Many genes affect hair color in mammals, but we’ll consider two primary genes that affect coat color in oldfield deer mice:

1. Melanocortin-1 receptor (Mc1r)

2. Agouti

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Genes Affecting Coat Color in Mice

Hopi Hoekstra and her colleagues have identified mutant alleles of these pigment genes that produce blond coloration in beach mice.

Dr. Hopi Hoekstra

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Melanocortin-1 receptor (Mc1r) Gene

The product of Mc1r is a transmembrane receptor protein that inserts into the plasma membrane of a melanocyte and signals the cell to produce black/brown eumelanin pigment.

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Why are Santa Rosa Island beach mice blond?

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Sand dunes of Santa Rosa Island, Florida

Hopi Hoekstra and her colleagues captured blond beach mice from the sand dunes of Santa Rosa Island, on Florida’s Gulf Coast. They found a point mutation in the Mc1r gene, changing one of the 954 base pairs that make up the gene.


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Due to a mutation altering a single base pair (CT) in the Mc1r gene, Santa Rosa beach mice have cysteine (a small, uncharged amino acid) at position 65 in the Mc1r transmembrane protein.

Field mice have arginine (a large, positively charged amino acid) in position 65.


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The Arg65Cys mutation in Santa Rosa Island beach mice reduces the ability of Mc1r to signal the melanocyte to produce black/brown eumelanin. Instead, melanocytes of mutant mice produce pheomelanin, a blond/red pigment.

A. The Arg65Cys mutation arose by chance, due to random substitution of one DNA nucleotide for another.

B. The Arg65Cys mutation arose because beach mice needed blond coloration in order to be camouflaged in their new habitat.

C. The Arg65Cys mutation arose due to natural selection for blond coloration.

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CQ#4: How did the Arg65Cys mutation arise?

A. The Arg65Cys mutation arose by chance, due to random substitution of one DNA nucleotide for another.

B. The Arg65Cys mutation arose because beach mice needed blond coloration in order to be camouflaged in their new habitat.

C. The Arg65Cys mutation arose due to natural selection for blond coloration.

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CQ#4: How did the Arg65Cys mutation arise?

Gulf Coast Beach Mice

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Dr. Hoekstra’s team examined the five Gulf Coast subspecies of beach mice, looking for the Arg65Cys mutation in the Mc1r gene.


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The Arg65Cys mutation is found in 4 of the 5 beach mouse subspecies found on the Gulf Coast, with varying frequency.


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Frequency of the Arg65Cys mutation correlates with coloration of the subspecies. •The darkest population (Alabama) lacks the mutation. •100% of the mice in the lightest population (Santa Rosa Island) have the mutation.

CQ #5: Four Gulf Coast subspecies share the Arg65Cys mutation. Select a possible explanation for this finding.

A. The Arg65Cys mutation arose independently in each of the four subspecies.

B. A single founding population with the Arg65Cys mutation colonized the beach habitat and differentiated into the four subspecies.

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It’s most likely that a single founding population with the Arg65Cys mutation colonized the beach habitat and differentiated into the four subspecies. However, it’s also possible that the mutation arose independently in each subspecies.

Work in your small groups to consider what additional information would help Dr. Hoekstra’s research team to distinguish between these two possible explanations.

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The Woolly MammothExamination of the DNA of a 43,000 year old woolly mammoth from Siberia found that one of the two alleles for the Mc1r gene showed the same Arg65Cys mutation as the beach mice! There was likely variation in fur color in mammoths.

54Red-haired woolly mammoth

CQ #6: Woolly mammoths and Santa Rosa Island beach mice share the Arg65Cys mutation. Select a likely explanation for this finding.

A. The Arg65Cys mutation arose independently in beach mice and mammoths.

B. The Arg65Cys mutation arose in a common ancestor to beach mice and woolly mammoths.

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A. The Arg65Cys mutation arose independently in beach mice and mammoths.

B. The Arg65Cys mutation arose in a common ancestor to beach mice and woolly mammoths.

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CQ #6: Woolly mammoths and Santa Rosa Island beach mice share the Arg65Cys mutation. Select a likely explanation for this finding.

Agouti Gene

• The Agouti gene is expressed in skin cells near the hair follicle and releases a small protein called Agouti.

• Agouti protein binds to Mc1r protein in the melanocyte membrane, preventing Mc1r from signaling the melanocyte to produce black/brown eumelanin.

• With inhibition of Mc1r, the melanocyte produces red/blond pheomelanin.

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Does Agouti contribute to blond coloration?

• Beach and mainland mice have Agouti proteins with identical amino acid sequences.

• Beach mice have mutations in Agouti that affect gene expression, not protein structure or function. The skin cells of Santa Rosa Island beach mice express Agouti at a higher rate than the skin cells of mainland mice.

How would increased expression of Agouti alter the coat color of these mice? Why?

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Atlantic Coast Beach Mice

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Three subspecies of beach mice live along Florida’s Atlantic Coast.

• Is the light coloration of the Atlantic Coast beach mice due to the same Arg65Cys mutation found in the Gulf Coast beach mice?

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Why are Atlantic Coast beach mice blond?

Anastasia Island beach mouse

• Is the light coloration of the Atlantic Coast beach mice due to the same Arg65Cys mutation found in the Gulf Coast beach mice?

• No! None of the Atlantic Coast subspecies have the Arg65Cys mutation that contributes to blond coloration.

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• Mc1r does not appear to be responsible for the blond coloration of Atlantic Coast beach mice.

• Are mutations in the coding or regulatory regions of Agouti responsible?

• The Hoekstra lab continues to work on this question…

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Atlantic and Gulf Coast Beach Mice

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It seems that different mutations in different genes lead to blond color in Atlantic Coast and Gulf Coast subspecies of beach mice.

Gulf Coast beach mouse

Atlantic coast beach mouse

CQ #7: What is the best explanation for these genetic differences?

A. Gulf Coast beach mice evolved from Atlantic Coast beach mice.

B. Atlantic Coast beach mice evolved from Gulf Coast beach mice.

C. Gulf Coast and Atlantic Coast beach mice evolved independently from populations of mainland field mice.

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Why did blond fur evolve in beach mouse populations?

Ultimate explanation:

Blond mice suffer reduced predation by visual predators. With increased survival, blond beach mice are more likely to reproduce successfully and have higher evolutionary fitness than dark beach mice.

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How did blond fur evolve in beach mouse populations?

Proximate explanation #1:

A point mutation in the Mc1r gene altered the protein coded by that gene by one amino acid (Arg65Cys). Mc1r could no longer signal melanocytes to make eumelanin.

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Proximate explanation #2: A mutation in the regulatory region of the Agouti gene increased gene expression, producing more Agouti protein. Agouti binds to Mc1r on the melanocyte membrane and prevents signaling to trigger eumelanin production.

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Part II (Simplified Version)

The Genes and Alleles Affecting Coat Color in Mice

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How is fur coloration determined?

• Mammals are unique in having hair or fur.• As each hair grows, cells at the base of

the hair follicle produce pigments that are deposited in the growing hair.

• Mammals can deposit a light pigment (red/blond) or a dark pigment (black/brown).

• Pigment molecules may also vary in distribution and number.

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Genes Affecting Hair Color

Many genes affect hair color in mammals, but we’ll consider two primary genes that affect coat color in oldfield deer mice:

1. Melanocortin-1 receptor (Mc1r)

2. Agouti

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Hopi Hoekstra and her colleagues have identified mutant alleles of these pigment genes that produce blond coloration in beach mice.

Dr. Hopi Hoekstra

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Genes Affecting Coat Color in Mice

Melanocortin-1 receptor (Mc1r) gene

The Mc1r gene determines whether light (blond/red) or dark (black/brown) pigments are deposited in the growing hair.

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Sand dunes of Santa Rosa Island, Florida

Hopi Hoekstra and her colleagues captured blond beach mice from the sand dunes of Santa Rosa Island, on Florida’s Gulf Coast. They found a point mutation in the Mc1r gene, changing one of the 954 base pairs that make up the gene.


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All of the Santa Rosa Island beach mice had a mutation in the Mc1r gene, causing them to produce the light pigment and deposit it in their fur.


CQ #4: How did the Mc1r mutation causing light fur arise?

A. The Mc1r mutation arose by chance, due to a random error during DNA replication.

B. The Mc1r mutation arose because beach mice needed blond coloration in order to be camouflaged in their new habitat.

C. The Mc1r mutation arose due to natural selection for blond coloration.

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A. The Mc1r mutation arose by chance, due to a random error during DNA replication.

B. The Mc1r mutation arose because beach mice needed blond coloration in order to be camouflaged in their new habitat.

C. The Mc1r mutation arose due to natural selection for blond coloration.

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CQ #4: How did the Mc1r mutation causing light fur arise?


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Dr. Hoekstra’s team examined the five Gulf Coast subspecies of beach mice, looking for the Arg65Cys mutation in the Mc1r gene.


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The Mc1r mutation is found in 4 of the 5 beach mouse subspecies, with varying frequency.


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Frequency of the Mc1r mutation correlates with coloration of the subspecies. •The darkest population (Alabama) lacks the mutation. •100% of the mice in the lightest population (Santa Rosa Island) have the mutation.

CQ #5: Four Gulf Coast subspecies share the Mc1r mutation for light fur. Select a possible explanation for this finding.

A. The Mc1r mutation arose independently in each of the four subspecies.

B. A single founding population with the Mc1r mutation colonized the beach habitat and differentiated into the four subspecies.

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It’s most likely that a single founding population with the Mc1r mutation colonized the beach habitat and differentiated into the four subspecies. However, it’s also possible that the Mc1r mutation arose independently in each subspecies.

Work in your small groups to consider what additional information would help Dr. Hoekstra’s research team to distinguish between these two possible explanations.

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The Woolly MammothExamination of the DNA of a 43,000 year old woolly mammoth from Siberia found that one of the two alleles for the Mc1r gene showed the same mutation as the beach mice! There was likely variation in fur color in mammoths.

83Red-haired woolly mammoth

CQ #6: Woolly mammoths and Santa Rosa Island beach mice share the Mc1r mutation for light fur. Select a likely explanation for this finding.

A. The Mc1r mutation arose independently in beach mice and mammoths.

B. The Mc1r mutation arose in a common ancestor to beach mice and woolly mammoths.

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A. The Mc1r mutation arose independently in beach mice and mammoths.

B. The Mc1r mutation arose in a common ancestor to beach mice and woolly mammoths.

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CQ #6: Woolly mammoths and Santa Rosa Island beach mice share the Mc1r mutation for light fur. Select a likely explanation for this finding.

Agouti Gene

• The Agouti gene is expressed in skin cells near the hair follicle, producing a small protein.

• Agouti protein binds to the pigment-producing cells, causing them to produce the light blond/red pigment.

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Does Agouti contribute to blond coloration?

• Beach and mainland mice have Agouti proteins with identical amino acid sequences.

• Beach mice have mutations in Agouti that affect gene expression, not protein structure or function: The skin cells of Santa Rosa Island beach mice express Agouti at a higher rate than the skin cells of mainland mice.

How would increased expression of Agouti alter the coat color of these mice? Why?

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Atlantic Coast Beach Mice

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Three subspecies of beach mice live along Florida’s Atlantic Coast.

• Is the light coloration of the Atlantic Coast beach mice due to the same Mc1r mutation found in the Gulf Coast beach mice?

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Anastasia Island beach mouse

• Is the light coloration of the Atlantic Coast beach mice due to the same Mc1r mutation found in the Gulf Coast beach mice?

• No! None of the Atlantic Coast subspecies have the Mc1r mutation that contributes to blond coloration.

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• Mc1r does not appear to be responsible for the blond coloration of Atlantic Coast beach mice.

• Are mutations in the coding or regulatory regions of Agouti responsible?

• The Hoekstra lab continues to work on this question…

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Why are Atlantic coast beach mice blond?

Atlantic and Gulf Coast Beach Mice

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It seems that different mutations in different genes lead to blond color in Atlantic Coast and Gulf Coast populations of beach mice.

Gulf Coast beach mouse

Atlantic coast beach mouse





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Why did blond fur evolve in beach mouse populations?

Ultimate explanation: Blond mice suffer reduced predation by visual predators. With increased survival, blond beach mice are more likely to reproduce successfully and have higher evolutionary fitness than dark beach mice.

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Proximate explanation:

Mutations in the Mc1r and Agouti genes cause beach mice to produce the light pigment and deposit it in their fur.

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The Blond Mc1r Allele

Four subspecies of beach mice on the Gulf Coast of Florida share the mutant Mc1r allele that contributes to blond fur color.

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Part III: The Origin of the Blond Mc1r Allele


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• 100% of the mice in the lightest population (Santa Rosa Island) have the mutation.

• 3 other populations share the mutation with frequencies ranging from 10% to 75%.

Where did the blond allele come from?

Hopi Hoekstra and her colleagues addressed this question by studying the Santa Rosa Island population, in which the blond Mc1r allele is fixed.

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Hypothesis 1:The mutant allele was present in the ancestral oldfield mouse population that invaded the new beach habitat.

Hypothesis 2:The mutant allele arose in the beach mouse population after it colonized the beach habitat and quickly became fixed.

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Two Opposing Hypotheses

Mc1r is a small gene, made up of 954 base pairs that are expressed as a single transcript.

•Hopi Hoekstra’s team examined a DNA region of 4000 base pairs that includes the Mc1r gene. •They noted all the variant forms of this region that occurred in two populations: an Alabama oldfield mouse population and the Santa Rosa Island beach population.

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H1

H2

Origin of blond Mc1r mutant allele102

Work in your groups to decide what evidence would support each of

these two contrasting hypotheses.

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Hypothesis 1:The mutant allele was present in the ancestral oldfield mouse population that invaded the new beach habitat.

Hypothesis 2:The mutant allele arose in the beach mouse population after it colonized the beach habitat and quickly became fixed.

The results:

Most of the variant forms of the 4000 base pair region that included the Mc1r gene found in the Santa Rosa Island beach mouse population were also found in the Alabama field mouse population.

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CQ #8: Which hypothesis do these results support?

A. H1: The mutant allele was present in the ancestral oldfield mouse population that invaded the new beach habitat.

B. H2: The mutant allele arose in the beach mouse population after it colonized the beach habitat and quickly became fixed.

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A. H1: The mutant allele was present in the ancestral oldfield mouse population that invaded the new beach habitat.

B. H2: The mutant allele arose in the beach mouse population after it colonized the beach habitat and quickly became fixed.

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CQ #8: Which hypothesis do these results support?

Mutation arose in ancestral population

Mutation fixed in SantaRosa Island population

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In your groups, discuss why these results support the first hypothesis.

H1: The mutant allele was present in the ancestral oldfield mouse population that invaded the new beach habitat.

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The Evolution of Blond Coloration in Beach Mice

Dr. Hoekstra’s research tells a remarkably complete story of evolution by natural selection, explaining why, how, and where selection has favored the evolution of blond coloration in beach populations of oldfield deer mice.

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Selection in the Valley of Fire

You will now watch a brief film about another story of evolution by natural selection: The Making of the Fittest: Natural Selection and Adaptation.http://www.hhmi.org/biointeractive/making-fittest-natural-selection-and-adaptationPredation has selected for dark coloration in rock pocket mice living on lava fields in New Mexico’s Valley of Fire.

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http://www.hhmi.org/biointeractive/making-fittest-natural-selection-and-adaptation

http://www.hhmi.org/biointeractive/making-fittest-natural-selection-and-adaptation

Image CreditsSlides 1, 5, 6, 8, 63, 92, 99:Photo of Alabama Beach Mouse (Peromyscus polionotus ammobates) in the Bon Secour National Wildlife Refuge, Alabama. USFWS, p.d. http://digitalmedia.fws.gov/cdm/singleitem/collection/natdiglib/id/10113/rec/1

Slides 2:, 23, 35, 42, 72:Various photos of Hopi Hoekstra and lab, courtesy of Hopi Hoekstra.

Slides 3,4, and 8:Photo of Peromyscus polionotus, the oldfield mouse a.k.a. beach mouse. USFWS, p.d., https://commons.wikimedia.org/wiki/File:Peromyscus_polionotus_oldfield_mouse.jpg.

Slide 7, 49, 50, 51, 59, 78, 79, 80, 88, 98: Figure 1 in Steiner, C.C., H. Römpler, L.M. Boettger, T. Schöneberg, and H.E. Hoekstra. 2009. The Genetic Basis of Phenotypic Convergence in Beach Mice: Similar Pigment Patterns but Different Genes. Mol Biol Evol 26 (1): 35-45. doi: 10.1093/molbev/msn218. Used with permission of Oxford University Press.

Slides 13–16:Photo of courting Japanese cranes by Francesco Veronesi, CC BY-SA 2.0, https://www.flickr.com/photos/francesco_veronesi/15525814846/.

Slides 31–33:By NCCSTS, based on Figure 1 from Vignieri SN, Larson J, Hoekstra HE. 2010. The selective advantage of cryptic coloration in mice. Evolution. 64:2153-2158.

Slide 44:Photo of Dunes of Santa Rosa Island, Florida, by User:Danielos, CC-BY-SA-2.5, https://commons.wikimedia.org/wiki/File:Santarosaislanddunes.jpg.

Slides 43, 45, 46: By NCCSTS.

Slide 54:Photo of woolly mammoth restoration at the Royal British Columbia Museum, Victoria, British Columbia, by User:WolfmanSF, CC BY-SA 3.0, https://commons.wikimedia.org/wiki/File:Woolly_Mammoth-RBC.jpg.

Slides 60, 63-65, 89, 92, 93, 94, 105, 106: Photo of Anastasia Island Beach Mouse, US NPS, p.d., https://commons.wikimedia.org/wiki/File:Peromyscus_polionotus_phasma.jpg.

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Selection and the Blond Beach Mouse Selection and the Blond Beach Mouse by Joan Sharp Department of...

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