Parasites

Question 1

What is a parasite?

Answer 1

Something that consumes the tissues or body fluids of the organism on which it lives (the host). They typically harm but don’t immediately kill the organisms they eat (unlike predators).

Question 2

What are some examples of parasites?

Answer 2

Virus microparasite, castilleja miniata, cuckoo birds (brood parasites) and trematodes macroparasite.

Question 3

What are brood parasites?

Answer 3

Parasites that lay their eggs in the nest of others to avoid having to rear their own young.

Question 4

What are pathogens?

Answer 4

Microparasites that causes diseases. They do not directly consume the host tissue.

Question 5

What is an example of a pathogen?

Answer 5

Influenza.

Question 6

What are parasitoids?

Answer 6

Insects whose larvae feed on a single host and almost always kill it.

Question 7

What percentage of insect species are parasitoids?

Answer 7

10-20%.

Question 8

What is the basic lifecycle of parasites? (e.g. mosquito)

Answer 8

The mosquito injects sporozoites into a human’s blood when it feeds which penetrate the liver cells and develop into merozoites. These can infect the liver and produce new generations. They can also grow in red blood cells where they can lyse the cells. There are 48 hour cycles that cause fevers and chills. Some merozoites develop into male and female gametocycles that a feeding mosquito can ingest. Eventually sporozoites invade the salivary gland.

Question 9

What does malaria success depend on?

Answer 9

Surviving in two hosts, developing 3 different life forms and being transmitted correctly.

Question 10

What are the two hosts involved in malaria?

Answer 10

Liver cells and blood cells.

Question 11

What might parasites do to complete their lifecycle and give an example?

Answer 11

They can alter the behaviour of their host, such as hairworms induce water-seeking behaviour in their terrestrial hosts, causing suicide.

Question 12

How can transmission be improved of parasites?

Answer 12

They can change the host mating system.

Question 13

How do parasites affect host population size?

Answer 13

Evidence suggests there is strong negative effects on the population size.

Question 14

What is the issue with moving organisms around the world?

Answer 14

New parasites can be introduced to an area.

Question 15

How else can parasites affect communities?

Answer 15

They can affect the outcome of species interactions.

Question 16

What is virulence?

Answer 16

The harm done by a parasite to the host following an infection.

Question 17

What is the conventional wisdom hypothesis?

Answer 17

The idea that given enough time, a state of peaceful coexistance will become established between any host and parasite.

Question 18

What is the trade-off hypothesis?

Answer 18

It predicts there is a trade-off between the rate of transmission and the duration of infection. It assumes that virulence is the result pathogen population growth and that a virulent strain of parasite may increase in frequency if in the process of killing its hosts it sufficiently increases its chance of being transmitted. Virulence should be the result of the optimal compromise between length of infection and growth to maximise transmission.

Question 19

What are different methods of transmission for a parasite?

Answer 19

Sexual transmission and horizontal transmission.

Question 20

What is the difference between the different types of parasite transmission?

Answer 20

Horizontal transmission is the transmission of a parasite in a non-sexual interaction or non-parental way. It may involve a vector. Sexual transmission is via sexual interaction and vertical transmission is from a parent to offspring at or before birth.

Question 21

What is the experimental evidence for the evolution of virulence?

Answer 21

It was found that if researchers gave more opportunities for horizontal transmission, the viruses evolved higher virulence and higher reproductive rates than viruses with lower opportunity for horizontal transmission.

Question 22

What do hosts do in response to parasites significantly reducing their fitness?

Answer 22

They may evolve a response to prevent this reduction in fitness, such as chimps eat plants that contain chemicals that kill nematodes.

Question 23

How can parasitism lead to coevolution?

Answer 23

The host may respond to the parasite by producing mechanisms to stop their fitness being reduced/kill the parasite and the parasite will then also evolve.

Question 24

What is an arms race?

Answer 24

A conflict between two or more parties with a goal of having superior forces and weapons, resulting in a rapid escalation of technology.

Question 25

What may prevent an arms race from occuring between host and parasite?

Answer 25

The cost of resistance and virulence.

Question 26

Is there a way to stop the coevolutionary process?

Answer 26

Tolerance traits may reduce the impact of parasites on host fitness. It does not exert selection on the parasite.

Question 27

Are parasites sufficient to explain the occurence of cycles?

Answer 27

Cycle amplitude decreased with increasing application of anti-nematode drugs - suggests that nematode parasites shape population densities.

Question 28

What is the American chesnut case?

Answer 28

The parasite was introduced from CHina and was not virulent on its normal chinese host. However in the USA it reduced the population density of the host and there are no longer any viable populations of American Chestnut.

Question 29

What is red queen dynamics?

Answer 29

Evolutionary hypothesis that organisms must constantly adapt to survive against ever-evolving organisms.