Week 10, Nematoda

Question 1

Describe some biological and anotomical features of nematodes

Answer 1

→ Majority are < 1mm
→ They have no defined respiratory or circulatory systems
→ They rely on diffusion of water, gases, and metabolites in and out of their semi-permeable body walls and internal transport by mixing of the pseudocoelomic fluid as the nematode moves
→ Many are capable of cryptobiosis (the ability to enter a state of suspended metabolic activity during unfavourable environmental conditions, which can last for 30+ years).
→ All nematodes undergo four moults before becoming an adult
→ The first moult occurs inside the egg
→ They emerge as 2nd-stage juveniles.

Question 2

Why are nematodes such as Caenorhabditis elegans used as a model species for animal developmental biology?

Answer 2

Mainly because they’re transparent and have a simple morphology.

Question 3

T/F: Most nematodes are hermaphrodites.

Answer 3

False.
Most are dioecious, meaning they have separate male and female individuals. Some are androdioecious, meaning they are mostly hermaphrodites but have rare occurrences of males.

Question 4

What is cryptobiosis?

Answer 4

The ability to enter a state of suspended metabolic activity during unfavourable environmental conditions, which can last for 30+ years

Question 5

T/F: The third larval stage is what emerges from the egg.

Answer 5

False; it’s the second.

Question 6

What feature enables you to distinguish between the head- and tail-ends?

Answer 6

The esophageal bulb.

Question 7

What feature enables you to identify plant-parasitic nematodes?

Answer 7

Presence of a stylet (spear-like mouthpart).

Question 8

How would you distinguish between male and female nematodes?

Answer 8

Look for ovaries and/or undeveloped eggs. Males also have a small ‘spicule’ near their tail, just past their anus.

Question 9

How are the parasitic nematodes that cause Elephantiasis transferred?

Answer 9

Mosquitoes are the intermediate host and vector

Question 10

How are the parasitic nematodes that cause heartworm in dogs transferred?

Answer 10

Mosquitoes are the intermediate host and vector

Question 11

How are Trichinella spp. transferred?

Answer 11

Through ingestion of encysted striated muscle (meat). Pigs are the main vector to humans.

Question 12

T/F: Trichinosis isn’t something we need to worry about in Australia.

Answer 12

True.

Question 13

Explain how a nematode might attack an insect pest.

Answer 13

→ Juveniles are free-living in the environment
→ They enter the host insect and release bacteria that the nematode has a symbiotic relationship with
→ The insect dies, and the nematodes begin development
→ Nematodes reproduce inside the dead insect
→ Juveniles emerge from the dead insect
→ Rinse and repeat

Question 14

How are plant-parasitic nematodes dispersed?

Answer 14

Basically by any process that moves soil or plant tissue.

Question 15

What do the above-ground symptoms of nematode damage to plant roots look like?

Answer 15

They are non-specific, and could appear as nutrient deficiency, incipient wilting, stunting, poor yield, or plant death. Basically, if the plant looks buggered, it could be because of nematodes.

Question 16

T/F: Nematode damage tends to be worse and more noticeable in sandy soils. Why?

Answer 16

True. Sandy soils allow nematodes to move between plants more freely, so damage is more widespread. For crops grown with short spacing within-row and wide row spacing, the damage will be more noticeable within-row because the nematodes will have greater success migrating to the closer plants (within the same row).

Question 17

What is an ectoparasitic nematode?

Answer 17

One that remains on the outside of the plant.

Question 18

What is a semi-endoparasitic nematode?

Answer 18

One that partially penetrates the plant to feed.

Question 19

What is a migratory endoparasitic nematode?

Answer 19

One that migrates (chews its way) through plant tissues.

Question 20

What is a sedentry endoparasitic nematode?

Answer 20

One that remains sedentary within a plant root to feed.

Question 21

T/F: Stem and bulb nematodes also feed on plant shoots.

Answer 21

True.

Question 22

What do Seed gall nematodes feed on?

Answer 22

Apical meristems and seeds.

Question 23

What are foliar nematodes?

Answer 23

Ones that feed on leaves.

Question 24

Once they’ve gotten to the plant, how do Seed gall nematodes get to the seeds?

Answer 24

The J2 nematodes swim up the plant in a film of water., feed as ectoparasites, and then invade the developing seeds where they moult and reproduce.

Question 25

How do Seed gall nematodes go from one plant to another?

Answer 25

In different generations. The nematodes reproduce inside the seeds and the new J2 nematodes desiccate (cryptobiosis) and overwinter in the seed galls. They emerge from the seed in spring.

Question 26

What role do nematodes play in annual ryegrass toxicity?

Answer 26

A species of seed gall nematode, Aguina spp., are vectors of R. toxicus (a bacterium) that produces a powerful poison called crynetoxin that can kill livestock that eat the infected seed heads.
Can be managed by preventing grass pastures from producing seeds.

Question 27

How (where) do foliar nematodes reproduce?

Answer 27

They penetrate the leaves through the stomata and lay their eggs inside the leaf, where the eggs hatch and the juveniles develop into adults.

Question 28

How do foliar nematodes migrate from one plant to another?

Answer 28

→ Get washed off one plant and swim up another
→ Undergo cryptobiosis and overwinter on dead plant leaves, then swim up another plant (in a film of water) in Spring (or whenever conditions are favourable).

Question 29

Which type of nematodes are likely to be transported by blowing/moving leaves from one place to another?

Answer 29

Foliar nematodes (overwintering on the dead leaves).

Question 30

What is the main difference between plant-feeding nematodes and fungi-feeding nematodes?

Answer 30

Fungi-feeding nematodes have a very short stylet or piercing structure.

Question 31

What type of mouthparts do bacteria-feeding nematodes have?

Answer 31

A ‘plain’ mouth region that looks just like an opening. Another way to think of it is that the head looks like the head of a pair of pliers - a top and bottom with a gap in the middle.