Name: Natural Selection: Calculating Fitness and Selection - Concept
Uploaded: 2019-01-31T09:27:05.000Z
Duration: 6 min 48 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Biology

Biological Evolution- Unity and Diversity

LS.Bio.9.1

Natural Selection

lab manual sub articles

Lab Manual Sub Articles

<p>Have you ever heard the phrase, survival of the fittest? When most people hear this phrase, they think of physical fitness features such as speed, strength and endurance. But what do biologists really mean by fitness?</p>
<p>It all started when Charles Darwin published The Origin of Species in 1859 which aroused much debate. Darwin&#39;s Theory of Natural Selection, which he defined as, '&#8230;the principle by which each slight variation, if useful, is preserved.' sparked the interest of a prominent 19th Century thinker, Herbert Spencer. In his book, Principles of Biology, Spencer coined the phrase, 'survival of the fittest', to explain Darwin&#39;s Natural Selection. This phrase resonated with many including Darwin himself and the term fitness became popular. </p>
<p>However, when biologists think of an organism&#39;s fitness, they don&#39;t think about its strength, speed or endurance. Instead, they simply consider fitness as the reproductive success of an organism relative to others. Take these Snowshoe Hares for example. Organisms with greater relative fitness have adaptations that allow them to have more offspring that survive and reproduce. These adaptations are called phenotypes defined simply as a visual expression of a trait. For example, Snowshoe Hares are brown in summer, but grow a white coat when the temperature drops. The ability to change fur color allows Snowshoe Hares to camouflage. Since hares with white winter coats are less visible to predators in the snow, survival rates are much higher for hares that turn white in winter. As a result, more color changing hares will survive to reproduce in summer. </p>
<p>To determine whether selection against a phenotype is taking place scientists calculate the fitness of each phenotype known as relative fitness, or 'w'. This is done by multiplying the survival rate - which is the proportion of that phenotype surviving - by the reproductive rate for each phenotype, which is the average litter size per mating season. Then, the product value of each phenotype is divided by the highest product value among the phenotypes.</p>
<p>Once scientists know the relative fitness, they can calculate the selection coefficient, or 's', which is the strength of selection against a phenotype, by subtracting relative fitness from 1. Higher numbers mean stronger selection against that individual phenotype. Scientists can use survival, relative fitness and selection coefficients to figure out if populations may be changing over time. For example, after the Industrial Revolution, the survival and relative fitness of light- colored peppered moths declined and the selection coefficient against them increased. The effect on the population of melanic moths was exactly the opposite, because conditions were favorable to their survival. After the passage of the Clean Air Act, the soot cleared up and the survival, relative fitness, and selection coefficient values for both phenotypes moved in opposite directions - which shows that selection favored the light moths again. </p>
<p>In general, the majority of biological traits with different potential phenotypes show a normal distribution. Let&#39;s take the spots on this group of ladybugs as an example. We can see that they have a varied number of spots from zero up to 12, but the average trait value is in the middle - referred to as a normal distribution as most of the ladybugs in this population have six spots. The height of the curve indicates the number of individuals in the population displaying the given trait. Now imagine that there is selection against the ladybugs with few or no spots because they absorb less heat and don&#39;t survive so well in cold temperatures. This would be an example of directional selection which favors extreme values of a trait in one direction. </p>
<p>To understand another type of selection, let&#39;s look at robins. If a female robin lays five or more eggs in a single clutch, the risk of malnourishment increases for the chicks. But if the robins lay three or less eggs, they may not have viable offspring. So here, stabilizing selection is holding a trait, egg clutch size, but an optimum value&#8230;any deviation from which is disadvantageous. Hence, most robins lay four eggs. </p>
<p>In West Africa, large billed black-bellied seed cracker finches easily break bigger hard seeds of one type of sedge grass while small billed finches effortlessly maneuver and break the smaller seeds of a different type of sedge. Medium billed finches cannot open either seed as efficiently and so are rarely observed. This type of selection is referred to as disruptive - where extremes of a phenotype are optimal which creates a bimodal distribution that deviates from the normal. </p>
<p>In this lab, you will model four population scenarios using pipe cleaners of varying colors and lengths representing different phenotypes and then determine the type of selection occurring in each scenario.<br />
 </p>

natural selection

<h4>Fitness</h4>
<p>Widespread variation of phenotypes in natural populations provides the raw material for evolution, which is the change in the inherited traits of populations over successive generations. Natural selection is one of the main mechanisms of evolution and requires variable traits to be heritable and associated with differential survival and/or reproductive success. Phenotypes that correlate with greater success will have more offspring that survive to reproduce in the next generation, and will thus be represented at greater levels in each successive generation.</p>
<p>The reproductive success of an organism relative to others is known as its fitness and any heritable trait that contributes to an organism&#39;s fitness is known as an adaptation. Therefore, individuals or phenotypes with higher lifetime reproductive success are considered to be more fit and better adapted to their environment.</p>
<p>An example of differential fitness comes from the snowshoe hare, which is brown in summer but grows a white coat in winter to camouflage in snow. Nonetheless, hares that maintain their brown summer coats throughout the year would be at a fitness disadvantage due to their relatively higher visibility to predators. Therefore, higher predator visibility would decrease the survival rate of the brown coat phenotype relative to the white coat phenotype, consequently reducing its lifetime reproductive success. Climate change, however, threatens organisms that fail to adapt to conditions, thus researchers have been studying how snowshoe hares are coping with warmer temperatures and decreased snow cover in winter. Snowshoe hares that grow a white coat in environments with diminished snow cover become more visible to predators, which reduces their reproductive success. Researchers have found that snowshoe hares did not alter their behavior to adapt to mismatch in their camouflage<sup>1</sup> and mismatched hares experienced significant decreases in their survival rates<sup>2</sup>.</p>
<p>Calculation of fitness relies on the relative survival and reproductive rates of different phenotypes in a population. For a given phenotype, survival rate is the proportion of that phenotype surviving, and reproductive rate is the average offspring produced per individual. The ratio between the products of the survival and reproductive rates for the different phenotypes is known as relative fitness (<em>w</em>). Hence, to calculate <em>w</em> for each phenotype (or trait), first the multiplication product of the survival and reproductive rates are calculated for individual phenotypes, this is then divided by the highest product value amongst them.</p>
<p><em>w</em> = (<em>Survival<sub>A</sub></em> x <em>Reproduction<sub>A</sub></em>) / (<em>Survival<sub>max</sub></em> x <em>Reproduction<sub>max</sub></em>)</p>
<p>This equation can be used in turn to calculate the strength of selection on different phenotypes, or the selection coefficient (<em>s</em>), by subtracting <em>w</em> from 1. Therefore, the value of the selection coefficient ranges between 0 and 1; the lower the value, the higher the selection against the specific trait. Thus, a phenotype that has a maximum fitness of 1.0, will be experiencing no selection.</p>
<p><em>s</em> = 1 &#8211; <em>w</em></p>
<h4>Selection</h4>
<p>There are three main types of selections: directional, stabilizing, and disruptive. Directional selection favors extreme values of a trait in one direction and can be induced by a change in the environment that the population needs to adapt to. One example is the evolution of differential jaw structures of East African cichlid fish in accordance with the diet source<sup>3</sup>. Stabilizing selection holds a trait at an optimum value; it is generally assumed that any deviation from this optimum is disadvantageous. For example, human fetus size is subject to stabilizing selection; babies born too small are less likely to survive and babies that are too big cannot pass through the birth canal during natural birth<sup>4</sup>. Disruptive selection favors two different extremes of a phenotype, creating a bimodal distribution. The evolution of West African seedcracker finch beaks resulted in two common phenotypes, large beaks that easily break hard sedge seeds and small beaks for soft seeds. Finches with medium beaks are not particularly good at consuming either seed type, thus are selected against<sup>5</sup>.</p>
<p>One of the most important ways natural selection impacts the lives of humans is through the rise of antibiotic resistant bacterial strains in hospitals and due to agricultural practices which utilize significant amounts of antibiotics<sup>6</sup>. The phenomenon of antibiotic resistance is a sort of inadvertent form of natural selection imposed by humans.</p>
<p>A question moving forward is whether natural populations will be able to adapt to the effects of climate change quickly enough to avoid extinction. This is dependent not only on existing variation in populations, but also on the strength of selection being high enough to affect quick change in the population. In this regard, reduced population sizes of many species around the world are of special concern.</p>
<h4>References</h4>
<ol class="references">
	<li><strong>Marketa Zimova, L. Scott Mills, Paul M. Lukacs, Michael S. Mitchell.</strong> Snowshoe hares display limited phenotypic plasticity to mismatch in seasonal camouflage. <em>Proc of the Royal Society. </em>2014, Vol. 281, 1782.</li>
	<li><strong>Nowak, Marketa Zimova L. Scott Mills J. Joshua.</strong> High fitness costs of climate change-induced camouflage mismatch. <em>Ecology Letters. </em>2016, Vol. 19, 3 (299-307).</li>
	<li><strong>R. Craig Albertson, J. Todd Streelman, and Thomas D. Kocher.</strong> Directional selection has shaped the oral jaws of Lake Malawi cichlid fishes. <em>PNAS. </em>2003, Vol. 100, (9) 5252-7.</li>
	<li><strong>Susan E. Hiby, Richard Apps, Olympe Chazara, Lydia E. Farrell, Per Magnus, Lill Trogstad, H&#229;kon K. Gjessing, Mary Carrington and Ashley Moffett.</strong> Maternal KIR in Combination with Paternal HLA-C2 Regulate Human Birth Weight. <em>J. Immunology. </em>2014, Vol. 192, (11) 5069-73.</li>
	<li><strong>Clabaut C, Herrel A, Sanger TJ, Smith TB, Abzhanov A.</strong> Development of beak polymorphism in the African seedcracker, Pyrenestes ostrinus. <em>Evol Dev. </em>2009, Vol. 11, (6) 636-46.</li>
	<li><strong>Witte, Wolfgang.</strong> Medical Consequences of Antibiotic Use in Agriculture. <em>Science. </em>1998, Vol. 279, (5353) 996-7.</li>
</ol>

Learn by watching this video about Natural Selection: Calculating Fitness and Selection - Concept at JoVE.com

Natural Selection: Calculating Fitness and Selection - Concept

Fitness
Widespread variation of phenotypes in natural populations provides the raw material for evolution, which is the change in the inherited traits of ...

Education

JoVE Lab Manual

Evolution

artificial selection

Artificial Selection

Natural Selection and Adaptive Evolution
In natural settings, adaptive evolution takes place by natural selection, a process in which differences in ...

hardy-weinberg and genetic drift

Hardy-Weinberg and Genetic Drift

Evolutionary change is interesting and important to study, but changes in populations occur over long periods of time and in huge physical spaces and are ...

evolutionary relationships

Evolutionary Relationships

Humans have been attempting to properly classify living things since Aristotle made the first attempt during the 4th century BC. Aristotle&#8217;s system ...

plant diversity

Plant Diversity

From Water to Land
Kingdom Plantae first appeared about 410 million years ago as green algae transitioned from water to land. Though challenging, this ...

animal diversity

Animal Diversity

Kingdom Animalia is composed of a range of organisms united by a set of common characteristics. Barring a few exceptions, animals are multicellular ...

microbial and fungal diversity

Microbial and Fungal Diversity

Bacteria and fungi are two highly diverse groups of organisms that can have significant beneficial or detrimental impacts on human health. For this ...

evolution

Learn how fitness, relative fitness, and selection coefficients explain natural selection, plus examples such as snowshoe hares, cichlid fish, and antibiotic resistance.

Fitness and Selection in Populations | JoVE K12

LS.Bio.9.4

Pennsylvania State Academic Standards

Life Science

Natural Selection and Evolution

3.1.9-12.T

3.1.9-12.U

3.1.9-12.W

Louisiana Student Standards for Science

High School

Life Sciences

Biological Evolution: Unity And Diversity

HS-LS4-2

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Mechanisms

Virginia  Standards of Learning

HIgh School

BIO.7

BIO.7.c

Minnesota Academic Standards in Science

3.2.1 9L.3.2.1.5

4.1.1

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

Biological Evolution: Unity and Diversity

HS-LS4-4

Arizona Science Standards

HS+B.L4

HS+B.L4U1.14

Alabama Course of Study Science

Unity and Diversity

9-12.B.4.14

Next Generation Science Standards

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance and Variation of Traits

HS-LS3-3

HS-LS4-3

Florida Department of Education

SC.912.L.15

SC.912.L.15.13

Texas Essential Knowledge and Skills

BIO.10

BIO.10.B

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

B-LS4-2.

B-LS4-3.

B-LS4-4.

new-york-state-science-learning-standards

New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS3-3.

HS-LS4-1.

HS-LS4-3.

HS-LS4-4.

Georgia Standards of Excellence

Ecology

SEC2.

SEC2.c

SB6.d

Prepare a natural selection simulation with pipe cleaners, tape, scissors, black and white construction paper, and student tables for partner stations.

Natural Selection Lab Materials Setup | JoVE K12

Model natural selection with pipe cleaners, color backgrounds, and grab-and-signal trials. Compare eyes-open and eyes-closed selection, fitness, and phenotypes.

Natural Selection in Pipe Cleaner Trials | JoVE K12

<ul><li><a href="#" data-time="4">Simulating Natural Selection
</a></li></ul>

<ol class="note-items"><li data-note-item="1" data-parent-collapse="">Simulating Natural Selection
<button class="expand">Expand</button><ul class="lab-items"><li data-sub-note-item="1-1"><div class="lab-step">To prepare for the lab, set out workstations for each student pair containing 6 white, 6 black, and 13 gray 12 inch pipe cleaners.
</div></li><li data-sub-note-item="1-2"><div class="lab-step">Then, add 62 pipe cleaners in any color but black, white or gray, a roll of tape, and a pair of scissors.
</div></li><li data-sub-note-item="1-3"><div class="lab-step">Also, place one piece of black construction paper and one piece of white construction paper at each station.
</div></li><li data-sub-note-item="1-4"><div class="lab-step">Finally, print out tables so that there are enough for each set of partners in the class.
</div></li><li data-sub-note-item="1-5"><div class="lab-step">To save materials for subsequent labs, inform students to save the materials and to avoid damaging them as much as possible.
</div></li></ul></li></ol>

<div class="section-question"><h4 class="question-sect">What is fitness?</h4><p>Fitness is the reproductive success of organisms relative to others.
</p></div><div class="section-question"><h4 class="question-sect">What is selection?</h4><p>Selection is one of the main mechanisms of evolution. It acts on heritable traits, enabling organisms with phenotypes that favor survival to produce more offspring than others with less favorable phenotypes.
</p></div><div class="section-question"><h4 class="question-sect">What are the survival and reproduction rates?</h4><p>Survival rate of a phenotype is the percentage of individuals with that phenotype to survive to reproductive age. Reproduction rate of a phenotype is the number of offspring generated by an average individual of that phenotype.
</p></div><div class="section-question"><h4 class="question-sect">How do we calculate fitness and selection? How do fitness and selection relate to each other?</h4><p>Relative fitness is the product of survival and reproduction rates of a phenotype divided by the value of the population&#8217;s most successful phenotype. Strength of selection for a phenotype depends on its relative fitness, since selection coefficient can be  calculated by subtracting relative fitness value of a phenotype from 1.
</p></div><div class="section-question"><h4 class="question-sect">What are the main types of selection and how do they differ?</h4><p>Main types of selection are directional, disruptive, and stabilizing. Directional selection favors extreme values of a trait in one direction. Disruptive selection favors two extremes of a phenotype in opposing directions. Stabilizing selection favors an optimum value.
</p></div>

Natural Selection: Calculating Fitness and Selection - Prep

Simulating Natural Selection
ExpandTo prepare for the lab, set out workstations for each student pair containing 6 white, 6 black, and 13 gray 12 inch ...

<p>To prepare for the lab, set out workstations for each student pair containing six white, six black and 13 gray, 12 inch pipe cleaners. Then add 62 pipe cleaners in any color but including black, white and gray, a roll of tape, and a pair of scissors. Also, place one piece of black construction paper and one piece of white construction paper at each station.</p><p>Finally, print out tables two through five so that there are enough for each set of partners in the class. To save materials for subsequent labs, inform students to save the materials and to avoid damaging them as much as possible. Please take time to review the material list and the student protocol video to be fully prepped for the lab.</p>

<ul><li><a href="#" data-time="6">Simulating Natural Selection
</a></li></ul>

<ol class="note-items"><li data-note-item="1" data-parent-collapse="">Simulating Natural Selection
<button class="expand">Expand</button><ul class="lab-items"><li data-sub-note-item="1-1"><div class="lab-step">To begin, cut the white, black, and gray pipe cleaners into quarters, which should produce a total of 100 pieces that are 3 inches long.
</div></li><li data-sub-note-item="1-2"><div class="lab-step">Then, cut the green pipe cleaners in the quantities and lengths specified in the video, taking care to minimize waste. This approximates a normal distribution of lengths and should result in an additional 100 pieces total. NOTE: One 12-inch pipe cleaner should yield multiple lengths, for example, a 5-inch piece and a 7-inch piece. Use this advantage to reduce waste.
</div></li><li data-sub-note-item="1-3"><div class="lab-step">Now, cut one sheet of black and one sheet of white construction paper into approximately 3-inch strips measured along the long edge of the paper.
</div></li><li data-sub-note-item="1-4"><div class="lab-step">Tape these strips down to cover the base of a dissecting tray to create an alternating pattern of black and white strips. NOTE: In the first simulation, you will use the white, gray, and black pipe cleaner segments against a black and white background to simulate different selection pressures due to predation on a population. You will select your prey using two different strategies, eyes-open and eyes-closed. For each of these strategies, you will perform four rounds consisting of 25 selections, alternating between two partners. After each round you will restore the population back to its original size using the proportions of phenotypes present after selection.
</div></li><li data-sub-note-item="1-5"><div class="lab-step">To begin the first scenario, count out 12 white, 12 black, and 26 gray pipe cleaner segments with your partner. Hypotheses: Here the experimental hypothesis might be that different predation strategies, such as having the eyes open or closed, will result in distinct selection pressures on the populations. Further, different phenotypes may be positively selected in the alternate scenarios. The null hypothesis might be that different predation strategies will have no effect on the populations or phenotypes.
</div></li><li data-sub-note-item="1-6"><div class="lab-step">Mix the pipe cleaner segments together as best as possible. Then, sprinkle them into the papered tray. NOTE: Ideally, the pipe cleaners will be spread out. However, this may not occur due to their self-adhering nature.
</div></li><li data-sub-note-item="1-7"><div class="lab-step">Once the segments are in the tray, separate them as best as possible without moving them too far from where they landed. As few segments as possible should be touching.
</div></li><li data-sub-note-item="1-8"><div class="lab-step">Have the first partner close their eyes. When given an audible signal by the second partner, the first should open their eyes and grab the first pipe cleaner they see from the tray as quickly as possible.
</div></li><li data-sub-note-item="1-9"><div class="lab-step">Set the removed pipe cleaner to the side.
</div></li><li data-sub-note-item="1-10"><div class="lab-step">Alternating partners, repeat this process a total of 25 times (steps 8 &#8211; 9).
</div></li><li data-sub-note-item="1-11"><div class="lab-step">Count the remaining pipe cleaners by color and record this in the data collection table for Scenario 1. <a href="https://www.jove.com/CDNSource/lm/labs/23/Lab_23_Tables_1_and_2.xlsx" style="display:block;margin:20px;" target="__blank">Click Here to download Tables 1 and 2</a>
</div></li><li data-sub-note-item="1-12"><div class="lab-step">Then, restore the population to 50 by adding one pipe cleaner of the same color for each of the remaining pipe cleaners. Hold these to the side until they are all gathered.
</div></li><li data-sub-note-item="1-13"><div class="lab-step">Then, sprinkle the pipe cleaners into the tray as previously described (steps 6-7). Repeat this process for three more rounds consisting of 25 selections each and record the counts for each of the rounds in the data collection table for Scenario 1.
</div></li><li data-sub-note-item="1-14"><div class="lab-step">Remove all pipe cleaners from the tray after the fourth round.
</div></li><li data-sub-note-item="1-15"><div class="lab-step">For Scenario 2, again count out 12 white, 12 black, and 26 gray pipe cleaner segments and sprinkle them randomly into the tray.
</div></li><li data-sub-note-item="1-16"><div class="lab-step">Follow the same protocol as in Scenario 1. However, when given the signal, the grabbing partner should keep their eyes closed. To aid in accuracy, it may help to position the hand near to the tray before grabbing.
</div></li><li data-sub-note-item="1-17"><div class="lab-step">Repeat this process 25 times, switching partner roles, and record the remaining pipe cleaner amounts in the data collection table for Scenario 2.
</div></li><li data-sub-note-item="1-18"><div class="lab-step">Then, restore the population to 50 based on that count. Do this for all four rounds. NOTE: In the second simulation, you will be using the eyes-open and eyes-closed predation strategies as previously described to select pipe cleaners of various lengths.
</div></li><li data-sub-note-item="1-19"><div class="lab-step">For Scenario 3, gather all 100 of the pipe cleaners that have been cut to varying lengths to represent different phenotypes.
</div></li><li data-sub-note-item="1-20"><div class="lab-step">One partner should hold all the pipe cleaners upright and loosely in one hand resting on the tabletop, such that the bottom end of each pipe cleaner rests against the tabletop.
</div></li><li data-sub-note-item="1-21"><div class="lab-step">Now, the partner that is not holding the pipe cleaners should close their eyes. When given an audible signal, the partner should open their eyes and grab the first pipe cleaner they see from their partner&#39;s hand.
</div></li><li data-sub-note-item="1-22"><div class="lab-step">Repeat this process 50 times (step 21). However, the partners should not switch roles during the round this time. The partner holding the pipe cleaners should always be the one giving the signal and never grabbing from the bunch.
</div></li><li data-sub-note-item="1-23"><div class="lab-step">After the first round consisting of 50 selections, count the remaining pipe cleaners by length. Then, record this information in the data collection table for scenario three. <a href="https://www.jove.com/CDNSource/lm/labs/23/Lab_23_Tables_3_and_4.xlsx" style="display:block;margin:20px;" target="__blank">Click Here to download Tables 3 and 4</a>
</div></li><li data-sub-note-item="1-24"><div class="lab-step">Add one pipe cleaner of the same length as each of the remaining ones to restore the population to 100. This will likely require more pipe cleaners than were originally cut. Try to use scraps from the class to reduce waste.
</div></li><li data-sub-note-item="1-25"><div class="lab-step">Repeat this for three more rounds, alternating which partner holds or grabs each round.
</div></li><li data-sub-note-item="1-26"><div class="lab-step">To perform Scenario 4, gather the varied-length pipe cleaners in their original proportions.
</div></li><li data-sub-note-item="1-27"><div class="lab-step">Now repeat the grabbing process, as described in Scenario 3. However, only remove 30 pipe cleaners instead of 50.
</div></li><li data-sub-note-item="1-28"><div class="lab-step">Divide the count at the end of each round by two for each phenotype 4 inches or below, rounding fractions down.
</div></li><li data-sub-note-item="1-29"><div class="lab-step">Then, record these values in the data recording table for Scenario 4.
</div></li><li data-sub-note-item="1-30"><div class="lab-step">Use the relative proportions of the phenotypes in the final population to restore the population to 100. When restoring the population to 100, it may be necessary to calculate relative proportions of phenotypes.
</div></li><li data-sub-note-item="1-31"><div class="lab-step">Repeat this for three more rounds, again alternating holding and grabbing the pipe cleaners.
</div></li><li data-sub-note-item="1-32"><div class="lab-step">For each scenario calculate the survival for each phenotype, that is the proportion of the phenotype surviving.
</div></li><li data-sub-note-item="1-33"><div class="lab-step">Then, calculate the relative fitness, or w, between each round. As reproductive rate does not vary in this simulation, this should always be considered equal, or 1.
</div></li><li data-sub-note-item="1-34"><div class="lab-step">Also, calculate the selection coefficients for each phenotype.
</div></li><li data-sub-note-item="1-35"><div class="lab-step">Now, use the relative frequencies of each phenotype to create histograms with appropriately labeled axes for each scenario showing the population before any selection took place and then alongside these in a different color after four rounds of selection.
</div></li><li data-sub-note-item="1-36"><div class="lab-step">Identify the type of selection taking place in each scenario and label the graphs. 
</div></li><li data-sub-note-item="1-37"><div class="lab-step">Develop a hypothesis to explain your observations. 
</div></li></ul></li></ol>

Natural Selection: Calculating Fitness and Selection - Procedure

Simulating Natural Selection
ExpandTo begin, cut the white, black, and gray pipe cleaners into quarters, which should produce a total of 100 pieces that ...

<p>To begin, cut the white, black, and gray pipe cleaners into quarters, which should produce a total of 100 pieces three inches long. Then cut the green pipe cleaners in the quantities and lengths listed here, taking care to minimize waste. This approximates a normal distribution of lengths and should result in an additional 100 pieces total.</p><p>One 12-inch pipe cleaner should yield multiple lengths, for example, a five-inch piece and a seven-inch piece. Use this advantage to reduce waste. Now cut one sheet of black and one sheet of white construction paper into approximately three-inch strips measured along the long edge of the paper.</p><p>Tape these strips down to cover the base of a dissecting tray to create an alternating pattern of black and white strips. In the first simulation, you will use the white, gray, and black pipe cleaner segments against a black and white background to simulate different selection pressures due to predation on a population. You will select your prey using two different strategies, eyes-open and eyes-closed.</p><p>For each of these strategies, you will perform four rounds consisting of 25 selections, alternating between two partners. After each round you will restore the population back to its original size using the proportions of phenotypes present after selection. To begin the first scenario, count out 12 white, 12 black, and 26 gray pipe cleaner segments with your partner.</p><p>Here the experimental hypothesis might be that different predation strategies, such as having the eyes open or closed, will result in distinct selection pressures on the populations. Further, different phenotypes may be positively selected in the alternate scenarios. The null hypothesis might be that different predation strategies will have no effect on the populations or phenotypes.</p><p>Mix the pipe cleaner segments together as best as possible. Then sprinkle them into the papered tray. Ideally the pipe cleaners will be spread out.</p><p>However, this may not occur due to their self-adhering nature. Once the segments are in the tray, separate them as best as possible without moving them too far from where they landed. As few segments as possible should be touching.</p><p>Have the first partner close their eyes. When given an audible signal by the second partner, the first should open their eyes and grab the first pipe cleaner they see from the tray as quickly as possible. Set the removed pipe cleaner to the side.</p><p>Alternating partners, repeat this process a total of 25 times. Count the remaining pipe cleaners by color and record this in the data collection table for scenario one. Then restore the population to 50 by adding one pipe cleaner of the same color for each of the remaining pipe cleaners.</p><p>Hold these to the side until they are all gathered. For example, if there were five gray pipe cleaners left in the tray, add five gray pipe cleaners to the pile. Then sprinkle the pipe cleaners into the tray as previously demonstrated.</p><p>Repeat this process for three more rounds consisting of 25 selections each and record the counts for each of the rounds in the data collection table for scenario one. Remove all pipe cleaners from the tray after round four. For scenario number two, again count out 12 white, 12 black, and 26 gray pipe cleaner segments and sprinkle them randomly into the tray.</p><p>Follow the same protocol as in scenario number one. However, when given the signal, the grabbing partner should keep their eyes closed. To aid in accuracy, it may help to position the hand near to the tray before grabbing.</p><p>Repeat this process 25 times, switching partner roles, and record the remaining pipe cleaner amounts in the data collection table for scenario two. Then restore the population to 50 based on that count. Do this for all four rounds.</p><p>In the second simulation, you will be using the eyes-open and eyes-closed predation strategies as previously described to select pipe cleaners of various lengths. For the third simulation, gather all 100 of the pipe cleaners that have been cut to varying lengths to represent different phenotypes. One partner should hold all the pipe cleaners upright and loosely in one hand resting on the table top such that the bottom end of each pipe cleaner rests against the table top.</p><p>Now, the partner that is not holding the pipe cleaners should close their eyes. When given an audible signal, the partner should open their eyes and grab the first pipe cleaner they see from their partner's hand. Repeat this process 50 times.</p><p>However, the partners should not switch roles during the round this time. The partner holding the pipe cleaners should always be the one giving the signal and never grabbing from the bunch. After the first round consisting of 50 selections, count the remaining pipe cleaners by length.</p><p>Then record this information in the data collection table for scenario three. Add one pipe cleaner of the same length as each of the remaining ones to restore the population to 100. This will likely require more pipe cleaners than were originally cut.</p><p>Try to use scraps from the class to reduce waste. Repeat this for three more rounds, alternating which partner holds or grabs each round. To perform the fourth scenario, gather the varied-length pipe cleaners in their original proportions.</p><p>Now repeat the grabbing process from scenario number three. However, only remove 30 pipe cleaners instead of 50. Divide the count at the end of each round by two for each phenotype four inches or below, rounding fractions down.</p><p>Then record these values in the data recording table for scenario four. Use the relative proportions of the phenotypes in the final population to restore the population to 100. When restoring the population to 100, it may be necessary to calculate relative proportions of phenotypes if the final count is more or less than 50.</p><p>Repeat this for three more rounds, again alternating holding and grabbing the pipe cleaners. Upon completion of all scenarios, gather the pipe cleaners and sort by size and color. Return the pipe cleaners to the front of the class for reuse by other lab sections and dispose of any waste.</p><p>For each scenario calculate the survival for each phenotype. That is the proportion of the phenotype surviving. So for example, if 83%of white pipe cleaners remain, this translates to a survival rate of 0.83.</p><p>Then calculate the relative fitness, or w, between each round. As reproductive rate does not vary in our simulation, this should always be considered equal, or one. Also, calculate the selection coefficients for each phenotype.</p><p>Now use the relative frequencies of each phenotype to create histograms with appropriately labeled axes for each scenario showing the population before any selection took place and then alongside these in a different color after four rounds of selection. Identify the type of selection taking place in each scenario and label the graphs. Why do you think each scenario led to the observed selection type?</p>

Development of Antibiotic Resistance

Antibiotic resistance is a major public health concern that arises when bacteria evolve mechanisms to withstand the effects of antibiotic treatments. This ...

Understanding Species and Reproductive Barriers

A species is a group of organisms that interbreed and produce fertile offspring. Typically, individuals of the same species appear similar and share ...

Formation of Species

Speciation describes the formation of one or more new species from one or sometimes multiple original species. The resulting species are discrete from the ...

Speciation Rates

Speciation can proceed at markedly different rates, and evolutionary biologists commonly describe these differences through the models of gradualism and ...

Genetics of Speciation

Speciation is the evolutionary process resulting in the formation of new, distinct species&#x2014;groups of reproductively isolated populations.The ...

Hybrid Zones

Hybrid zones are narrow regions where two closely related species interact, mate, and produce hybrids. Relative to either parent species, hybrids may ...

What is Natural Selection?

Natural selection is an evolutionary process in which individuals with survival-promoting traits reproduce at higher rates. These favorable traits become ...

Types of Selection

Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural ...

Frequency-dependent Selection

When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to ...

Limits to Natural Selection

Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly ...

Observing Artificial Selection in Plants
ExpandTwo weeks before beginning the pollination experiments, collect a sufficient amount of small pots with a ...

Observing Artificial Selection in Plants 
ExpandTo begin the experiment, collect five two-week old grown plants from the generation one population that ...

Analyze and interpret data to summarize how various factors such as geographic isolation, pesticide resistance, antibiotic resistance can influence natural selection.

Phylogenetic Trees

Phylogenetic trees come in many forms. It matters in which sequence the organisms are arranged from the bottom to the top of the tree, but the branches ...

Conditions on Early Earth

Around 4 billion years ago, oceans began to condense on earth while volcanic eruptions released nitrogen, carbon dioxide, methane, ammonia, and hydrogen ...

The Colonization of Land

Changes in the environment of the early Earth drove the evolution of organisms. As prokaryotic organisms in the oceans began to photosynthesize, they ...

What is Evolutionary History?

Scientists record evolutionary history by analyzing fossil, morphological, and genetic data. The fossil record documents the history of life on Earth and ...

The Evidence for Evolution

Genetic variations accumulating within populations over generations give rise to biological evolution. Evolutionary changes can result in the formation of ...

The Fossil Record

The fossil record documents only a small fraction of all organisms that have ever inhabited Earth. Fossilization is a rare process, and most organisms ...

Convergent Evolution

Evolution shapes the features of organisms over time, ensuring that they are suited for the environments in which they live. Sometimes, selection pressure ...

Gene Evolution - Fast or Slow?

The genomes of eukaryotes are punctuated by long stretches of sequence which do not code for proteins or RNAs. Although some of these regions do contain ...

genome-size-and-the-evolution-of-new-genes

Genome Size and the Evolution of New Genes

While every living organism has a genome of some kind (be it RNA, or DNA), there is considerable variation in the sizes of these blueprints. One major ...

Gene Families

Gene families consist of groups of genes proposed to have originated from a common ancestor. Typically these arise through events in which a gene or genes ...

types-of-genetic-transfer-between-organisms

Types of Genetic Transfer Between Organisms

Genetic transfer occurs when genetic information is passed from one organism to another. It occurs via two mechanisms: vertical gene transfer and ...

Ribozymes

The term ribozyme is used for RNA that can act as an enzyme. Ribozymes are mainly found in selected viruses, bacteria, plant organelles, and lower ...

Construct an explanation to illustrate how common ancestry and biological evolution are supported by multiple lines of empirical evidence.

LS.Bio.9.2

Use models to illustrate the conditions required for natural selection, including the overproduction of offspring, inherited variation, and the struggle to survive.

LS.Bio.9.3

Construct an explanation to explain how natural selection leads to adaptations within populations.

Extinction

The History of Life on Earth
Fossils of organisms that were different from anything alive today had been documented as early as the 17th century, but it ...

Diversity and Extinction during the Paleogene Epoch
ExpandFirst, familiarize yourself with the extinction reading supplement for the background on what ...

Diversity and Extinction during the Paleogene Epoch
ExpandBegin this procedure by reading the extinction reading supplement that has been printed out for ...

Construct explanations to illustrate how varying environmental conditions may result in: changes in the number of individuals of a species, the emergence of new species over time, or the extinction of other species.

LS.Bio.10.1

Synteny and Evolution

John H. Renwick first coined the term &#8220;synteny&#8221; in 1971, which refers to the genes present on the same chromosomes, even if they are not ...

Multi-species Conserved Sequences

Next-generation sequencing technologies have created large genomic databases of a variety of animals and plants. Ever since the human genome project was ...

Taxonomy

Taxonomy is the science of defining and naming groups of biological organisms based on shared characteristics. It uses a hierarchy of increasingly ...

Phylogeny

Phylogeny is concerned with the evolutionary diversification of organisms or groups of organisms. A group of organisms with a name is called a taxon ...

Use models (including dichotomous keys, scientific nomenclature, cladograms, phylogenetic trees) to identify organisms and exemplify relationships.

LS.Bio.10.2

Understand natural selection as a mechanism for biological evolution.

Natural Selection

Description

Fitness

Transcript

Tags

More videos by Standards