Expedition Evolution
Name(s) ______________________________________ Date _________
Activity 3. Developing Hypotheses
(video segment 03:27 – 07:44)
Use what you have learned about evolution, predators, and mosquitofish to predict how populations of
mosquitofish might differ between blue holes with predators and those without predators. Use Table 1
There are a few things you need to know about mosquitofish before you get started.

Mosquitofish find food in the shallows and in open water.

Having good endurance helps mosquitofish move around and get more food.

Eating more food and growing bigger increases mosquitofish reproduction.

A mosquitofish can’t be both a good sprinter and good endurance swimmer.

Mosquitofish that are good sprinters are more successful at avoiding predators.
Table 1. Traits of Mosquitofish Living in Blue Holes With and Without Predators.
Trait
Time spent in open water
No predators
With predators
If different, why?
Sprint speed
Endurance
Reproductive age
Activity 4. Analyzing Data (video segment 07:49 – 11:37)
Let’s test your predictions! We’ll start with the behavior of mosquitofish.
Calculate the average proportion of fish that are found in open habitats and shallow habitats and
record them in each table below.
Table 2. Proportion of Mosquitofish in Shallow and Open Water Habitats With Predators.
Proportion in open
water (%)
1
Proportion in
shallow water (%)
99
Yes
0
100
Sooner’s
Yes
2
98
Cousteau’s
Yes
0
100
Billy’s Leap
Yes
2
98
Average
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Blue hole
Deep Blue
Predators present?
Yes
Gracie’s
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Table 3. Proportion of Mosquitofish in Shallow and Open Water Habitats Without Predators.
Proportion in open
water (%)
29
Proportion in
shallow water (%)
71
No
20
80
Pagreeps
No
38
62
Hansen’s
No
35
65
Little Blue
No
28
72
Average
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Blue hole
Wolfpack
Predators present?
No
Rainbow
1. Make a double bar graph of the average proportion of mosquitofish in open water and shallow water
habitats in blues holes with and without predators. (use table 2 & 3)
2. Was your prediction from activity 3 supported? Why or why not?
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It is really hard to measure the swimming speeds of mosquitofish, but we can look at the shape of their bodies.
Fish that accelerate well—the sprinters that can escape predators more easily—have bigger caudal peduncles than
those fish that are not good accelerators (see Figure 1). Fish that have better endurance have smaller caudal
peduncles.
Figure 1. This is an X-ray image
of two mosquitofish. The
caudal peduncle is circled in
each fish. The fish on top is
from a blue hole with many
predators. The bottom fish is
from a blue hole with few
predators.
3. In terms of caudal peduncle areas, state your predictions about how fish should differ in their sprint speeds
and endurance in blue holes with and without predators.
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Fill out the averages in the table below.
Table 4. Caudal Peduncle Areas (mm2) of Mosquitofish in Various Blue Holes.
Rainbow
Fish number
1
Wolfpack
No predators
Cousteau’s
Billy’s Leap
39.8
40.9
Predators present
44.9
46.0
2
35.5
40.8
46.1
45.8
3
36.4
39.4
45.7
46.1
4
36.4
40.2
49.2
44.6
5
40.1
39.5
47.4
46.4
6
39.8
49.0
47.4
47.9
7
39.1
41.5
43.6
48.9
8
40.9
38.1
47.0
44.1
9
39.3
39.9
46.6
47.5
10
38.7
38.8
44.5
44.4
Average
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4. Make a bar graph of the caudal peduncle areas of mosquitofish in the four blue holes. Be sure the graph
groups together the blue holes with predators and the blue holes without predators. (use table 4)
5. Suppose that a bird flew to Rainbow blue hole with eggs of sleeper gobies attached to its feet. After
many years, a large population of these predatory fish is established in Rainbow blue hole. You explore
the blue hole after many generations of mosquitofish have lived with these predators. How do you think
these mosquitofish would differ from the ones that are there today? Why?
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Humans are changing ecosystems all over the world. In some places, predators are being driven to near
extinction. For example, large sharks are disappearing from many oceans. In other places, new predators
are being introduced. For example, pythons from Asia are now slithering around the Florida Everglades.
Humans are also agents of evolutionary change. Human fishing and hunting can cause natural selection
just as predators do.
6.
Based on what you have learned, what do you think would happen to the reproduction age and
total body sizes of fish species that are heavily fished by people? Why?
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