Parasitic Modes of Life

Question 1

Define commensalism.

Answer 1

Literally ‘eating at the same table’ but NO metabolic dependence - purely ecological relationship. Both able to olive full lives without other member of relationship.

Question 2

Define phoresis.

Answer 2

Transport and shelter with no metabolic interactions.

Question 3

What is an example of a commensal relationship?

Answer 3

Clownfish and sea anemones.

Question 4

What is an example of a phoresic relationship?

Answer 4

The defenceless pearl fish Fieraster that is an inquiline species living in the respiratory trees of holothurians.

Question 5

Define inquiline.

Answer 5

House guest.

Question 6

Define mutualism.

Answer 6

Associations where both species gain benefits but the association is not obligatory, e.g. cleaner fish and shrimps.

Question 7

What can symbiotic relationships be divided into?

Answer 7

Intra- and inter-specific forms.

Question 8

What is the difference between facultative and obligate symbiotic relationships?

Answer 8

Obligate: both parties depend on each other to survive.
Facultative: they do not require each other to live.

Question 9

What are examples of symbiosis?

Answer 9

Anglerfish - dwarf males.
Echiurans - same.
Vent worms - riftia - chemoautotrophic bacteria.
Algae and fungi form lichens.

Question 10

What is the difference between predation and parasitism.

Answer 10

Predators kill and eat prey species on their first encounter, whereas parasites feed on their hosts, reducing the life span but not as an immediate consequence of the encounter.

Question 11

What is a parasitoid?

Answer 11

An intermediate stage between predation and true parasitism. They attack themselves or lodge within a host, consuming it and eventually killing it.

Question 12

What is an example of a parasitoid?

Answer 12

The Phronima arthropod eating salps, and fish leeches. Mostly insects tho.

Question 13

What is an ecto-parasite and what is an endo-parasite?

Answer 13

Ecto lives outside and endo lives inside.

Question 14

Define facultative.

Answer 14

Can survive as free-living but can also become fully functional parasite, e.g. some ciliates.

Question 15

Define obligate.

Answer 15

Must find a receptive host in order to complete their life cycle.

Question 16

What is a temporary parasite?

Answer 16

They infect for short periods, e.g. leeches, & verge on predation. When they revisit a host they may be PERIODIC.

Question 17

What is a permanent parasite?

Answer 17

They remain with their host until they have completed the appropriate stage in their life cycle, and may be harboured by the host for long periods, sometimes decades in the case of gut helminths in long-lived vertebrates.

Question 18

What are larval parasites?

Answer 18

Those with parasitic juvenile stages.

Question 19

What is an example of a parasitic larvae?

Answer 19

The ‘praniza’ larvae of some isopods. They have huge jaws to attack to fish skin, where it feeds on blood & mucus & can cause serious mortalities in juvenile fish. Eventually drop off and metamorphose on bottom. Adults free-living and inhabit burrows in sand/algal mats w/ harem of females.

Question 20

What are hyperparasites?

Answer 20

Parasites of parasites.

Question 21

What is an example of a hyperparasite?

Answer 21

Monogenean Udonella, that parasitises an ectoparasitic copepod Caligus rogercresseyi found on the Chilean rock cod.

Question 22

What are microparasites?

Answer 22

Very small compared to hosts & have short generation times, often w/ life spans shorter than hosts. Often provoke strong immune responses from vertebrate hosts.

Question 23

What is an example of a microparasite?

Answer 23

Protists and small helminths. Giardia causes severe gastrointestinal effects which may help to increase its dispersal and infection of new hosts.

Question 24

What are macroparasites?

Answer 24

They generally do not multiply with on on their hosts and have relatively long generation times. They induce little or no host immune response, depending on the severity of the infection. They do cause weakening of the host and produce morbidity rather than mortality.

Question 25

How is the severity of an infection expressed?

Answer 25

Mean Worm Burden (MWB)

Question 26

What does morbidity involve?

Answer 26

Increased chances of secondary infection or predation, or decrease in chances of reproduction.

Question 27

What is a direct life cycle?

Answer 27

Those where there is a single host, e.g. gill monogeneans that have a parasitic adult form and a free-living larval stage.

Question 28

What are indirect life cycles?

Answer 28

Those with several hosts that can be characterised by their relationship to the parasite life cycle.

Question 29

What are the three groups of hosts found in indirect life cycles?

Answer 29

Definitive & Intermediate Hosts (Permissive)
Accidental Hosts (Permissive & Non-Permissive)
Paratenic Hosts (Partially Permissive)

Question 30

What is a definitive host?

Answer 30

The host in which sexual reproduction takes place, producing eggs or more rarely larvae.

Question 31

What is an intermediate host?

Answer 31

The host containing the asexual phase of the life cycle but often represent a multiplication stage.

Question 32

What are accidental hosts?

Answer 32

Species not normally part of the life cycle but in permissive forms the parasite is able to complete its life cycle, but in non permissive forms it fails to develop and dies.

Question 33

What are paratenic hosts?

Answer 33

Hosts that ingest larval stages and carry them in a form of arrested development, accumulating them until they have a chance of infecting a definitive host. They are not essential and sometimes called transport hosts.

Question 34

Why are parasites always smaller than their host but larger than free living forms?

Answer 34

1) Unlimited and secure food supply from hosts.
2) Selective pressure favouring larger and more fecund parasites, since the greater the no. of offspring the greater the new host chances.
3) 2 is counterbalanced by pressure to minimise damage to host so as to maximise survival and ensure it covers parasite life span.

Question 35

How do parasites deal with reproduction problems?

Answer 35

They are often hermaphroditic, parthenogenetic (produce sterile young) or asexually reproducing, to maximise the ability of an isolated individual to create a population.

Question 36

What is sacculinisation?

Answer 36

Simplification of body forms, lacking sensory structures and motility because such functions are redundant. They may evolve new structures for attaching or copulation.

Question 37

How do parasites disperse young? Why is it required?

Answer 37

To exploit new resources and prevent excessive inbreeding, & maximising the chances of finding a new host. Done by host migration or water currents.

Question 38

How do parasites infect their hosts?

Answer 38

Oral ingestion.
Injection by intermediate host (less common in marine)
Transdermal burrowing.

Question 39

What is host specificity?

Answer 39

The parasitic equivalent of habitat selection. Some spp infect a wide range of hosts, but some are very very specific.

Question 40

How can parasites directly alter the behaviour of their hosts?

Answer 40

By physical and biochemical disruption of neurohormonal systems, often seen in invertebrate intermediate hosts.

Question 41

How do parasites avoid triggering a host immune response?

Answer 41

They carry out surface absorption of host antigens, molecular mimicry, loss/masking of surface antigens, antigenic variation, occupation of immunologically incompetent sites (CNS) and immunosuppression.

Question 42

Define symbiosis.

Answer 42

Close and often longterm interaction between two or more different biological species.

Question 43

What are the 6 parasitic attributes?

Answer 43

1) Recognition of suitable host site.
2) Maintenance of position.
3) Adaption to physico-chemical conditions of host.
4) Non-lethal exploitation of host’s nutrients.
5) Avoidance of recognition by host immune responses.
6) Synchronisation with host life cycle.