NAME DATE

CSI: Changing Species Investigation

Tuskless Elephants
This file contains real data about elephant populations. Is there evidence of natural selection? You’re
on the case!

Species Profile
African elephants are sometimes poached, or
illegally hunted, for their ivory tusks. The ivory
is carved into ornaments and jewelry. Adult
elephants have the biggest tusks, so elephants
are often killed around the age they would have
calves (babies). Some elephants never grow
tusks at all, so they are not killed for ivory.

Poaching is happening less in some places, but

in others it’s still a big problem for elephant
populations.

Is the tuskless trait helpful, harmful, or neutral?

Circle the most likely answer for each environment.

1. In the time before poaching, the tuskless trait was (helpful / harmful / neutral) to an elephant.

2. In the present with poaching, the tuskless trait is (helpful / harmful / neutral) to an elephant.

Prediction
Write a sentence about how poaching may affect the tuskless trait in elephant populations:

© 2022 University of Utah Updated June 10, 2022 1

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Have elephant populations changed over time?

To find out, you would ideally compare
tusklessness in today’s herds to tusklessness in
historic herds. But while we know tusklessness Serengeti
used to be rare, we don’t have exact numbers. National Park
Ugalla Game
Reserve Tarengire
There are some modern herds in protected
parks that experience low poaching. They can National Park
represent historic herds in your study. TANZANIA
Katavi
Time to do some field work! You travel National Park Protected
Poached
to different parks in Tanzania and count Ruaha
elephants with and without tusks. National Park

Let’s analyze your data!

Complete the table (calculate the percent of tuskless elephants). Then make a
bar graph of your findings.

Elephant Total Tuskless Percent Percent Tuskless Elephants by Location

10
Population Elephants Elephants (%)
8
Tuskless
% Tuskless

6
Tarangire 443 4
4
Serengeti 364 5
2
Ruaha 329 23
0
Katavi 413 26 Tarangire Serengeti Ruaha Katavi Ugalla

Ugalla 153 15 Protected Poached

Summarize the evidence. Complete the summaries by circling the correct words:

3. In poached populations, the percent of tuskless elephants is (lower / higher) than in protected
populations.

4. The evidence suggests that the tuskless trait has become:

(more common / less common / stayed the same).

5. Does the evidence suggest tusklessness in elephant populations is influenced by poaching?

(yes / no)

© 2022 University of Utah CSI: Changing Species Investigation 2

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Is the tuskless trait inherited?

While you investigated parks in Tanzania, other researchers observed elephants in South Africa’s
Addo National Park. The herd is protected now, but was once heavily poached. Nearly all the
females are tuskless. The image below shows the only mothers that do have tusks and their
daughters.

Count the daughters and fill in the top row of the table.
Mothers Total Number Number of Tuskless Number of Tusked
of Daughters Daughters Daughters

Tusked
Tuskless 161 160 1

Summarize the evidence:

Calculate from the top row of the table...

6. Tusked mothers have tuskless daughters % of the time.

7. Tusked mothers have tusked daughters % of the time.

Calculate from the bottom row of the table...

8. Tuskless mothers have tuskless daughters % of the time.

9. Tuskless mothers have tusked daughters % of the time.

10. The evidence suggests the tuskless trait is (heritable / acquired).

Is it natural selection?
Write 2–3 sentences to explain your thinking:

© 2022 University of Utah CSI: Changing Species Investigation 3

NAME DATE

CSI: Changing Species Investigation

Insecticide-resistant Bedbugs
This file contains real data about bedbug populations. Is there evidence of natural selection? You’re
on the case!

Species Profile
Bedbugs are blood-sucking insects. They hide in
bedding and furniture during the day, and sneak
out to feed at night. A bedbug bite causes an itchy
rash.

Bedbugs were a problem until the 1950s. Then a

strong insecticide was invented, and they mostly
disappeared. For a long time, “sleep tight, don’t
let the bedbugs bite” was nothing more than a
children’s rhyme.

Now bedbugs are back. The insecticide that nearly

killed them off isn’t used anymore because it’s bad for the environment. New, safer insecticides
worked at first. But as they’re used more, they don’t work as well. The ability of a bedbug to survive
insecticide toxins is a trait called insecticide resistance (IR).

Is the IR trait helpful, harmful, or neutral?

Circle the most likely answer for each environment.

1. Before insecticides were invented, the IR trait was (helpful / harmful / neutral) to a bedbug.

2. Today with insecticide use, the IR trait is (helpful / harmful / neutral) to a bedbug.

Prediction
Write a sentence about how insecticide use may affect the IR trait in bedbug populations:

© 2022 University of Utah Updated June 10, 2022 4

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Have bedbug populations changed over time?

To find out if IR in bedbugs has changed, you’ll compare bedbugs that have been exposed to
modern insecticide to those that have not.

Your research team collects bedbugs from cities in Michigan and Ohio where bedbugs have made
a comeback. You also have a lab population that was collected from New Jersey 30 years ago. It has
never been exposed to modern insecticides. In your notes, you’ll refer to each population by where
it came from:

• Fort Dix, New Jersey: no insecticide exposure

• Troy, Michigan: exposed to insecticide
• Cincinnati, Ohio: exposed to insecticide
You applied 1,000 nanograms of insecticide to representatives from each bedbug population, then
counted how many bedbugs were killed.

Let’s analyze your data!

Fill in the table and make a bar graph of your findings.

Percent Bedbugs Killed
by Location
Percent Bedbugs Killed by Location
Bedbug Number Number Percent (%)
Population Treated Killed Killed
100

90

Fort Dix 60 60 80

70
Troy 60 16 60

50
Cincinnati 60 17
% Killed

40

30

20

10

0
Fort Dix Troy Cincinnati
No past
Past insecticide exposure
insecticide exposure
Summarize the evidence. Complete the summaries by
circling the correct words:

3. The IR trait is (lower / higher) in exposed bedbugs, compared to non-exposed bedbugs.

4. Evidence suggests the IR trait has become (more common / less common / stayed the same).

5. Does the evidence suggest the IR trait in bedbug populations changed over time from
insecticide use? (yes / no)

© 2022 University of Utah CSI: Changing Species Investigation 5

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Is insecticide resistance inherited?

Insects with IR often have proteins that can quickly break down
the insecticide, before it has toxic effects. Proteins are coded
for by genes, which pass from parents to their offspring.

You want to find out if protein differences are causing the IR

trait in bedbugs.

From each bedbug population, you collect two proteins: EST

and GST. Then, you test each protein’s ability to break down Protein Activity
insecticide. To do that, you test how much of the protein’s 100

% Target Broken Down in 1 minute

90
target it can break down in 1 minute.
80
70
60

Summarize the evidence. Complete the summaries by 50

circling the correct words: 40

30
6. Proteins that break down insecticide are (more active 20

/ less active) in exposed bedbugs, compared to non- 10

exposed bedbugs. 0

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T
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7. The evidence suggests the IR trait is (heritable / acquired).

Fo
Fo
EST Enzyme GST Enzyme

Is it natural selection?
Write 2–3 sentences to explain your thinking:

© 2022 University of Utah CSI: Changing Species Investigation 6

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CSI: Changing Species Investigation

Tail white in juncos
This file contains real data about junco populations. Is there evidence of natural selection? You’re on
the case!

Species Profile
You can find dark-eyed juncos in the mountains of the
American West. They hop about the forest floor, making a
“chip chip” sound.

Individual juncos have different amounts of white in the

feathers along the edges of their tails (we’ll call this the
tail white trait). When male juncos court females, they fan
out their tails to show off their white feathers. Females
prefer mates with more tail white.

In 1983, a group of juncos moved from the mountains

to the coastal area around the University of California
San Diego (UCSD). Their descendants still live there.
Local birdwatchers have noticed these birds look a little
different. Males have less tail white.

The coastal birds have a different lifestyle from their mountain cousins. The mild climate makes their
breeding season longer, and they can raise up to four broods each year (mountain birds usually raise
one). The coastal birds are also less crowded, and birds are visible across greater distances. Most
males find a mate.

Is the tail white trait helpful, harmful, or neutral?

Circle the most likely answer for each environment.

1. In the past when all juncos lived in the mountains, the tail white trait was (helpful / harmful /
neutral) to a bird.

2. In today’s coastal population, the tail white trait is (helpful / harmful / neutral) to a bird.

Prediction
Write a sentence about how the environment (for example, mate preference) may affect the tail
white trait in junco populations:

© 2022 University of Utah Updated June 10, 2022 7

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Has the bird population changed over time?

To find out if tail white has changed, you would ideally compare the trait in today’s coastal birds to
their ancestors soon after they arrived from the mountains. But since you can’t travel back in time,
the next best thing is to compare the coastal birds to their mountain cousins.

You catch 10–27 male birds from each study site, photograph their tail feathers, and release the
birds. Then you measure the percent of white in each bird’s tail from your photos. The table on the
next page lists your measurements for representative birds from each location.

Let’s analyze your data!

Fill in the table and make a bar graph of your findings.

Average Percent White in
Location % White in Tail of Average
Tail Feathers by Location
Representative % White 50
Birds in Tail
Laguna Mountains 52, 46, 48, 37, 39
Cleveland National 50, 50, 45, 37, 48 45

Forest
% White
San Bernardino 51, 43, 57, 36, 29
National Forest 40

Winema National 37, 35, 35, 52, 43

Forest
35
Coastal 43, 30, 32, 37, 38

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Mountain

Summarize the evidence. Complete the summaries by circling the correct words:
3. The percent white in tail feathers is (lower / higher) in coastal birds, compared to their mountain
cousins.

4. If mountain birds represent past populations, and coastal birds the present, the percent of white
tail feathers has (increased / decreased / stayed the same).

5. Does the evidence suggest tail white in junco populations is influenced by the environment they
live in? (yes / no)

© 2022 University of Utah CSI: Changing Species Investigation 8

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Is tail white inherited? Tail White

60
To test if tail white is inherited, you gather eggs
from nests in the mountains and the coast. Then Wild Hand-raised
50
you care for them in identical conditions.
40
When the chicks reach adulthood, you compare
the tail feathers of hand-raised and wild birds. Your

% White
30
data is shown on the graph.
20
Summarize the evidence. Complete the
summaries by circling the correct words: 10

6. For hand-raised vs. wild birds, tail white is 0

(different / about the same).

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as

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Co

ou

Co
ou
7. For hand-raised coastal vs. hand-raised

M
M
mountain birds, tail white is
(different / about the same).

8. The evidence suggests tail white is (heritable / acquired).

Is it natural selection?
Write 2–3 sentences to explain your thinking:

© 2022 University of Utah CSI: Changing Species Investigation 9

NAME DATE

CSI: Changing Species Investigation

Winged aphids
This file contains real data about aphid populations. Is there evidence of natural selection? You’re on
the case!

Species Profile
Aphids are tiny insects that suck sap from plants. They’re
the opposite of picky eaters! If you have a garden, take a
close look at any plant. There’s a good chance you’ll find
aphids.

Aphids reproduce quickly. A mother can have around 80

nymphs (young offspring) in a week. The nymphs take
about a week to grow up, then they have offspring of their
own.

Most aphids don’t have wings. They tend to live on

the plant where they were born. It gets crowded fast.
Sometimes there are so many that they literally suck the
life out of the plant. Not surprisingly, gardeners have
watched aphids closely. And they noticed something.
When the aphids got crowded, some developed wings as
they grew up. The winged aphids could fly away to new
plants.

Is the winged trait helpful, harmful, or neutral?

Circle the most likely answer for each environment.

1. Before a plant gets crowded, the winged trait is (helpful / harmful / neutral) to an aphid.

2. When a plant gets crowded, the winged trait is (helpful / harmful / neutral) to an aphid.

Prediction
Write a sentence about how crowding may affect the winged trait in aphid populations:

© 2022 University of Utah Updated June 10, 2022 10

NAME DATE

Have aphid populations changed over time?

To test if the winged trait in aphids can change, you collect some wingless adults. You spread them
out on healthy plants then watch for six generations as the aphids reproduce and become more
crowded. For every generation, you count the number of insects with wings.

Let’s analyze your data!

Fill in the table and make a bar graph of your findings.

Percent Winged Aphids Over Time
Generation Total Winged Percent (%)
50
Aphids Aphids Winged Aphids
1 15 0 40
2 54 0

% Winged
30
3 63 0
4 124 7 20

5 150 44
10
6 208 89
0
1 2 3 4 5 6

Generation

Summarize the evidence. Complete the summaries by circling the correct words:

3. The percent of winged aphids is (lower / higher) as insects become more crowded.

4. The winged trait has become (more common / less common / stayed the same).

Observation
While doing your experiment, you also tracked what happened when the winged aphids flew away
to non-crowded plants. The winged aphids had only wingless nymphs! In fact, you didn’t see any
more winged aphids until a few generations later when the insects were crowded once again.

Interpretation: Write a sentence that may explain your observation:

© 2022 University of Utah CSI: Changing Species Investigation 11

NAME DATE

Are aphid wings inherited? Winged Aphids by Condition

To find out if wings are inherited, you let nymphs from 25

wingless mothers grow up in either crowded or non-

crowded conditions. After lots of counting, you make this 20

graph of your data:

15

% Winged
Summarize the evidence. Complete the summaries by
circling the correct words: 10

5. Aphids grow wings in non-crowded conditions (often /

5
sometimes / never).

6. Aphids grow wings in crowded conditions (often / 0

sometimes / never). Non-crowded Crowded

7. The evidence suggests wings are (heritable / acquired).

Is it natural selection?
Write 2–3 sentences to explain your thinking:

© 2022 University of Utah CSI: Changing Species Investigation 12