Parasitism

Question 1

What is a parasite?

Answer 1

Organisms that feed on other organisms. They are dependent on other organisms for food and development. The fitness effects are negative.

Question 2

Name some common parasites

Answer 2

Malaria
Tapeworm
Nematodes
Wolbachia
brood parasites.

Question 3

What are parasite life cycles like?

Answer 3

The parasite is transferred from host to host. They are transferred via a vector e.g. a mosquito. They are transferred by water, soil, food, contamination.

Question 4

What is the difference between simple and complex life cycles?

Answer 4

Simple: Reproducing adults in the definitive host alternate with free living egg or larval stages.
Complex: Include additional larval stages in one or more intermediate host.

Question 5

What are some of the hurdles for parasites to overcome?

Answer 5

• Becoming attached to the host
• withstanding defences
• competitors and predators.

Question 6

How can hosts defended themselves?

Answer 6

CONSITUTIVE DEFENCES: Common to healthy animals, general protection to a wide range of parasites and diseases.
INDUCIBLE DEFENCES:
Turned on by exposure as a response to the infection. They are specific to the parasite.

Question 7

Explain host parasite phylogeny?

Answer 7

There is a tight association between host and parasite - their evolution is linked. Parasites have large population sizes, short generation times, high mutations and high migration.

Question 8

What is male-killing via Wolbachia?

Answer 8

Wolbachia is passed through the egg cytoplasm of females. In beetles, butterflies and flies male sones of infected females are killed. The hosts daughter benefits from the sons death due to reduced inbreeding and food scrambles. Infected females therefore have fitter daughters.

Question 9

Can parasites alter the predation risk?

Answer 9

Birds carry the flatworm parasite. It passes the eggs in its droppings. The larvae hatch and infect snails living close to water. They move into the digestive system, develop and gather in the tentacles. They create eye-catching patterns, and snails may seek the light - birds eat the snail.

Question 10

What are is brood parasitism?

Answer 10

The manipulation and use of the host to raise young. Can be interspecific or intraspecific.

Question 11

What is intraspecific brood parasitism?

Answer 11

Females lay eggs in the nest of other females. e.g. wood ducks, golden eyes. This alters reproductive success and behavioural interactions.

Question 12

What is interspecific brood parasitism?

Answer 12

Female uses the nest of a different species. Some are generalists e.g. cowbirds, some are specialists e.g. whydahs.

Question 13

What are adaptations to brood parasitism?

Answer 13

• removal of parasitic eggs by the host
• hiding of the nest
• identifying the parasite and killing it
• abandoning the nest and re-nesting.

Question 14

What are counter adaptations to responses from hosts?

Answer 14

• laying mimetic eggs
• specialising on one host
• destroying nests if eggs are rejected.

Question 15

What are the effects if brood parasitism on host populations?

Answer 15

• reduces reproductive success of the host
• reduces resources as they have to invest in rearing a larger bird.
• creates complex interactions with parasites taking revenge.

Question 16

What is kleptoparasitism?

Answer 16

The theft of resources. Commonly food, also nesting material and ornaments. This affects distribution, territory, population size, demography. Some species are opportunist some are obligate.

Question 17

Example of altered response behaviour?

Answer 17

AMPHIPODS: normally hide and burrow when disturbed. When infected with amphipod parasite they responded equally but when infected with a duck parasite, they behaved very conspicuously and floated close to the surface, slowed down swimming speed which increased duck predation.

Question 18

Example of fearlessness?

Answer 18

Changes in the neurochemical balance of mice infected with Eimeria. The infected did not show the same fear response as uninfected. They ignored the cat scent. They also had increased social interactions which transmits parasites from host to host.

Question 19

Example of altered appearance?

Answer 19

e.g. Trematode and snail.

Question 20

Altered activity and social behaviour?

Answer 20

The BANDED KILLFISH. When infected with a trematode black spots form. This makes them an easier target for predators. There are also population effects as fish prefer shoals with no infected individuals, the greater the amount of black the more they are discriminated.

Question 21

Example of exhaustion?

Answer 21

TAPEWORM: The definitive host are canids, the intermediate host is large mammals e.g. moose. The tapeworm overwhelms the host causing faster exhaustion and greater predation risk.

Question 22

Example of developmental deformities?

Answer 22

PACIFIC TREE FROGS. They suffer from limb deformities due to cysts forming in the limb buds. If cysts miss the limb buds more limbs are grown.

Question 23

Example of altered host predation?

Answer 23

Parasites mimic host prey. Parasites lure the hoist into eating them. This facilitates entry into the host. the benefits are that it is a safe environment to grow into adults, is a dependable food source an easy dispersal. However they are not guaranteed to find a host and the host could be eaten.