Modes of Selection

Warm up questionWhat are the 5 forces that drive the evolution of populations? What is the only way that is adaptive?

prior knowledge

Prior KnowledgeCFU: the 5 fingers of evolution could be whiteboards, TPS with random selection, PearDeck, etc1

Modes of Selection

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ObjectiveStudents will differentiate between various modes of selection, analyze shifts in numerical distribution of traits, and use these shifts as evidence that evolution by natural selection is occurring in a population, citing specific evidence from the data to justify their conclusions

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With your partner analyze this graph

investigationAt least 3 observations

http://www.radiolab.org/story/288733-23-weeks-6-days/

After students describe graph this 5 minute video from RadioLab is funWhat is the most common birth weight in pounds?Why is infant mortality higher for very large or very small babies?How might technology and medical advancements influence this graph going into the future?

This is called STABILIZING SELECTION it is just one way that natural selection influences the distribution of phenotypes in a population. Today we are going to learn about the 3 major modes of selection and how data can help us determine what mode of selection is at work.4

With your partner analyze this case studyhttps://www.youtube.com/watch?v=LyRA807djLc

How did the phenotypes of the moths change?

What factors drove those changes?

How is this case similar/different from the birth weight exampleinvestigation

2 minute video showing peppered moths5

Natural SelectionRequires:Variation in a population

prior knowledge

Prior Knowledge: In order for natural selection to occur, there must be differences between individuals in a population some will have traits that help them survive and reproduce better than others (remind students that DNA (genes) give us traits and variation)variation from random mutations, also sexual reproduction, crossing over, etc6

Natural SelectionRequires:Struggle for survival/competition

prior knowledge

Prior Knowledge: There must be competition and other limiting factors that lead to a struggle for existence (survival of the fittest)7

Natural SelectionChanging environment

prior knowledge

Prior Knowledge:There must be environmental resistance (pressure) natural or man-made. When environment is changing especially quickly, some populations adapt quickly, while others may die out. Can give examples like ice ages and interglacials, climate change, deforestation, etc. 8

Explain how this picture shows the evolution of a population by natural selection

Include the terms:VariationStruggleChanging environmentHow is new population better adapted?prior knowledge

CFU on prior knowledge: longer answers required here so perhaps think-write-pair-share?9

Modes of Natural SelectionNatural selection can occur 3 main ways depending on what phenotype in a population is favored

concept

New ConceptThese are pocket mice found in the deserts of New MexicoSand colored mice hide from predators best when on the sandBlack mice hide from predators best on the exposed lava rock10

Stabilizing SelectionNatural selection favors the average phenotype

concept

Have students draw a basic copy of this graph. 11

Stabilizing Selection example

Robins tend to lay 4 eggs each season. When they lay more eggs there may be too many offspring for the parents to provide food for all of themWhen they lay fewer eggs, there may not be any healthy offspring that hatch

concept

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Directional Selection

Natural selection favors one end of the range of phenotypes that are possibleconcept

Pushes population in a certain direction with regard to phenotype13

Directional Selection exampleDuring dry years, there are mostly only larger, tougher seeds available as food on the Galapagos islands. Birds with the largest beaks are favored during these times.

concept

Have students make a basic copy of this graph14

Disruptive SelectionNatural selection favors phenotypes at both ends of the range

concept

Here, it pays to be lightest and blend in with the sandy substrate OR darkest and blend in with the black lava rock. Intermediate rock pocket mice have decreased viability on both substrateshttps://www.hhmi.org/biointeractive/making-fittest-natural-selection-and-adaptation I just show the first 2 minutes or so of this video15

What type of natural selection is shown in the graph? How do you know?

concept check level 1This example shows ________ selection because ______________

Could add a sentence frame here if needed: This graph shows _______ selection because. Could do this as a TWPS or TPS. I might Pear Deck or whiteboard this because it is super basic everyone should be able to do it stuff16

What type of natural selection is shown in the graph? How do you know?

concept check level 1This example shows ________ selection because ____________

Could add a sentence frame here if needed: This graph shows _______ selection because. Could do this as a TWPS or TPS. I might Pear Deck or whiteboard this because it is super basic everyone should be able to do it stuff17

What type of natural selection is shown in the graph? How do you know?

This example shows ________ selection because ______________concept check level 1

Could add a sentence frame here if needed: This graph shows _______ selection because. Could do this as a TWPS or TPS. I might Pear Deck or whiteboard this because it is super basic everyone should be able to do it stuff18

What type of selection is at work? How do you know? Cite specific evidence

skill level 1

Ask students to cite specific evidence from the text to support their conclusions. Start video at 6 minutes and end at 9:15, or play all 15 minutes if you likehttps://www.hhmi.org/biointeractive/origin-species-beak-finch 19

What type of selection is at work? How do you know? What would a graph of this population look like?

skill level 1

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In wild populations of lilies, short stemmed plants do not receive enough sunlight to grow, while long stemmed flowers often suffer wind damage

skill level 1What type of selection is at work? How do you know? What would a graph of this population look like?

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What type of selection is at work? How do you know? What would a graph of the original and new populations look like? In a population of petunias, flowers with the brightest color attract the most pollinators whereas plants of moderate color or dull color are less likely to be visited by a pollinator and thus less likely to reproduce. Data of a population of petunias first grown in a greenhouse and then planted outdoors is given belowYear 2004Grown in greenhouseYear 2014Growing in the wildBrightly colored4080Moderate color8515Dull color255

skill level 2

Hand pollination could occur in the greenhouse population thus eliminating the need for wild pollinators. Ask students to cite specific data/evidence from the prompt in their answer. You might stress to students that in both cases (pollinators and finches), it was a fairly rapid change in the environment that led to directional selection. This is when we see directional selection most often. 22

What type of selection is at work? How do you know? What would a graph of the original and new populations look like? A desert population of spiny cacti are being eaten by an invasive species the peccary. Peccaries favor cacti with few spines.skill level 2

Number of cacti before introduction of peccariesNumber of cacti after introduction of peccariesMany spines407524Moderate spines388435Few spines32436

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What type of selection is at work? How do you know? What would a graph of the original and new populations look like? Just as the peccary and cacti populations are starting to adjust to each other, another invasive species arrives a parasitic wasp. The wasp lays her eggs on the cacti, and the grubs eat the soft inner flesh of the leaves, killing the plant. Wasps prefect plants with many spines to protect their grubs.How would this new species affect the distribution of phenotypes in the cacti population? skill level 2

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Graph this data and determine the mode of selection at work on the desert cacti population

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Number of spinesNumber of cacti0510152025300102030405060708090100110120130

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Number of spinesNumber of cacti0510152025300102030405060708090100110120130

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ObjectiveStudents will differentiate between various modes of selection, analyze shifts in numerical distribution of traits, and use these shifts as evidence that evolution by natural selection is occurring in a population, citing specific evidence from the data to justify their conclusionsclosure

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Independent Practice

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What type of selection is at work? How do you know?

Extra CFU31

What type of selection is at work? How do you know?

Extra CFU32

Draw a new curve on the graph below to show how the distribution of beak sizes might change as a result of selection in this new environment. A population of birds, with various size beaks, eats seeds. Small seeds can be eaten by birds with small beaks. Larger, thicker seeds can only be eaten by birds with larger, thicker beaks. Suppose there is a shortage of small seeds but that there are still many large seeds.

Extra CFU33