Exercise 13

Question 1

Why are parasites so abundant and why do they tend to be specialists?

Most host species have multiple parasites and those parasites have parasites.

Parasites tend to be specialists because they live on or in their hosts.

Parasites tend to be specialists because they feed on certain parts of the host’s body.

All of the above

Answer 1

All of the above

Question 2

What is an advantage of ectoparasitism?

Exposure to the external environment

Avoidance of natural enemies

Dispersal from one host individual to another

Ease of obtaining digested food of the host

Answer 2

Dispersal from one host individual to another

Question 3

What is an advantage of endoparasitism?

Exposure to the external environment

Avoidance of natural enemies

Dispersal from one host individual to another

Exposure to the host’s immune system

Answer 3

Avoidance of natural enemies

Question 4

Which is a mechanism that hosts do not use to defend themselves against parasites?

Resembling a palatable host

Immune system

Symbiont defense

Biochemical defenses

Answer 4

Resembling a palatable host

Question 5

Some hosts are aided in their defense against parasites by bacteria and fungi. What best describes this defense?

Biochemical defense

Symbiont defense

Immune defense

Encapsulation

Answer 5

Symbiont defense

Question 6

How can humans overcome the malaria parasite?

Encapsulation of the Plasmodium virus

Inject Plasmodium with virus-like particles

The spleen destroys red blood cells that contain Plasmodium

Red blood cells divide rapidly to starve the Plasmodium

Answer 6

The spleen destroys red blood cells that contain Plasmodium

Question 7

Coevolution is when populations of two interacting species evolve in which of the following ways?

Separately, each in response to the selection pressures imposed by the other

Separately, each in response to the selection pressures imposed by the environment

Together, each in response to the selection pressures imposed by the environment

Together, each in response to the selection pressures imposed by the other

Answer 7

Together, each in response to the selection pressures imposed by the other

Question 8

What factor(s) can affect the outcome of coevolution in host–parasite interactions?

The genetic diversity of the host

The mutation rate of the parasite

The lethality of the parasite

All of the above

Answer 8

All of the above

Question 9

Why don’t host–parasite interactions show an ever-escalating coevolutionary arms race?

Each species has too much genetic diversity.

There is a trade-off in which a parasite’s counterdefenses have no costs to growth, reproduction, or survival.

There is a trade-off in which a host’s defenses have costs to growth, reproduction, or survival.

There is a trade-off in which a host’s defenses have no costs to growth, reproduction, or survival.

Answer 9

There is a trade-off in which a host’s defenses have costs to growth, reproduction, or survival.

Question 10

Which study shows that parasites can cause population cycling in its host?

American chestnut and a parasitic fungus

Red grouse and nematode parasites

Amphipods and trematode parasites

Amphipods and trematode parasites

Answer 10

Red grouse and nematode parasites

Question 11

Which factor is not considered in host–parasite population models?

The number of susceptible hosts

The number of infected hosts

The number of susceptible parasites

The number of recovered and immune hosts

Answer 11

The number of susceptible parasites

Question 12

What are two ways to control the spread of a disease?

Decrease the susceptible hosts and increase the threshold density

Increase vaccines and programs that decrease the transmission rate

Kill or recover infected hosts

All of the above

Answer 12

All of the above

Question 13

How can parasites or pathogens affect species interactions?

A host may become more susceptible to predation.

A host may be better able to catch its prey.

A host may be a better competitor.

Both a and c

Answer 13

A host may become more susceptible to predation.

Question 14

When a population of the caddisfly Glossosoma nigrior was infected by a fungal pathogen, what were the community consequences and why?

A decrease in the abundance of dozens of species, all of which relied on the caddisfly

An increase in the abundance of dozens of species, all of which relied on the caddisfly

An increase in the abundance of dozens of species, all of which were negatively affected by herbivory of the caddisfly

An increase in the abundance of dozens of species, all of which were negatively affected by carnivory of the caddisfly

Answer 14

An increase in the abundance of dozens of species, all of which were negatively affected by herbivory of the caddisfly

Question 15

What is one type of pathogen vector that might cause disease spread in humans during climate change and why?

Rodents benefiting from warmer conditions

Mosquitos benefiting from increasing CO2

Sand flies benefiting from increasing wet conditions

Mosquitos benefiting from warmer conditions

Answer 15

Mosquitos benefiting from warmer conditions

Question 16

Suppose the researchers conducted another experiment to investigate whether other species of defensive symbionts can protect fruit flies from the nematode parasite Howardula. In the first experiment, they screened for beneficial symbiotic bacteria by searching for species similar to Spiroplasma bacteria. They first established a large population of fruit flies and exposed it to the nematode parasite. They then separated the fruit fly individuals into two groups: those without Howardula and those with Howardula. They screened individuals from both groups for seven species of symbionts (A–G). The results are shown in the table.

Experiment 1 Percentage of Fruit Fly Individuals with Different Species of Symbionts

                             Symbiont species

Treatment A B C D E F G

Howardula absent 50 40 80 30 50 95 30

Howardula present 50 90 10 30 75 95 96

Based on the data, which bacterial species appear to be defensive symbionts? Choose all that apply.

Species A
Species B
Species C
Species D
Species E
Species F
Species G

Answer 16

Species B,E,G

Question 17

Experiment 1 Percentage of Fruit Fly Individuals with Different Species of Symbionts

                             Symbiont species

Treatment A B C D E F G

Howardula absent 50 40 80 30 50 95 30

Howardula present 50 90 10 30 75 95 96

Refer to the data provided above.

Which bacterial species may have been negatively affected by parasitism? Choose all that apply.

Species A
Species B
Species C
Species D
Species E
Species F
Species G

Answer 17

Species C

Question 18

Refer to the information provided in the previous 2 questions.

Suppose in a second experiment the researchers follow, for seven generations, the percentage of fruit fly individuals that harbor the symbiont Species B with and without Howardula. They find the results shown in the table. Examine the data in the table. Do the results indicate that there is a cost to flies for harboring Species B symbiont?

Experiment 2 Percentage of Fruit Fly Individuals Harboring Species B Symbiont

                                Generation

Treatment 1 2 3 4 5 6 7

Howardula absent 39 43 30 22 15 6 1

Howardula present 75 80 86 92 97 99 99

There is no cost to flies for harboring species B symbiont because the symbiont protects the flies against Howardula.

There is no cost to flies for harboring Species B symbiont because the frequency of flies harboring the symbiont decline in the absence of the parasite.

There is a large cost to flies for harboring Species B symbiont because the frequency of flies harboring the symbiont decline in the absence of the parasite.

There is a large cost to flies for harboring Species B symbiont because the frequency of flies harboring the symbiont increases in the presence of the parasite.

Answer 18

There is a large cost to flies for harboring Species B symbiont because the frequency of flies harboring the symbiont decline in the absence of the parasite.

Question 19

The transmission coefficient of the hypothetical disease Dirks fever is 0.8. If the combined death and recovery rate is 0.4, what is the threshold density for Dirks fever?

Answer 19

0.4/0.8=0.5

Question 20

Which of the following should reduce the critical threshold for the spread of disease?

Decreasing the transmission of coefficient

Increasing the rate at which individuals die

Decreasing the rate at which individuals become immune

Increasing the density of susceptible individuals

Answer 20

Increasing the rate at which individuals die

Question 21

The Anopheles mosquito, which causes malaria, requires warm temperatures to complete the life cycle of Plasmodium falciparum. Which of the following statements is true?

If temperatures increase due to climate change, it is hypothesized that the incidences of malaria in humans and wildlife will increase.

If temperatures decrease due to climate change, it is hypothesized that the incidences of malaria in humans and wildlife will increase.

If temperatures decrease due to climate change, it is hypothesized that the incidences of malaria in humans and wildlife will increase.

If temperatures decrease due to climate change, it is hypothesized that the incidences of malaria will shift toward the poles.

Answer 21

If temperatures increase due to climate change, it is hypothesized that the incidences of malaria in humans and wildlife will increase.

Question 22

What is the advantage for a male cricket parasitized by hairworms to seek out water?

By hydrating the cricket, the water decreases the negative effects of the parasite.

Female crickets live near the water; by going to the water, the infected cricket can increase his chances of mating before the parasite kills him.

There is no advantage for the cricket; the cricket’s behavior is advantageous only to the parasite.

There is no advantage for the infected cricket, but by going to the water and drowning, the cricket reduces the prevalence of parasitism in the species.

Answer 22

There is no advantage for the cricket; the cricket’s behavior is advantageous only to the parasite.