NEMATODE EXCRETORY SYSTEM
Section through esophagus
Section through middle
Stylet
Median
Bulb
Lips
Procorpus
Excretory
Duct
Bursa
Spicules in cloaca
Intestine
Lobe of esophagus gland
overlapping intestine
Testis
Ovary
Intestine
Vulva
Egg
Postuterine Sac
(Present in species with 1 ovary)
Lateral
Lines
Anus
Tail
Basic Nematode Body Design
C.I.H. 1:21
D. destructor
NEMATODE EXCRETORY SYSTEM
Excretory canals run through lateral hypodermal cords.
Different systems = “H” (A, B), “U” (C), and tylenchoid (D).
A single “renette cell” (E) is present in Dorylaimida.
NEMATODE PHYSIOLOGY
EXCRETORY SYSTEM
Excretion of Nitrogenous Waste Products
-Ammonia, urea, or uric acid
-Amino acids, amines, peptides & fatty acids
-Aquatic organisms = live in soil water
-Ammonia toxic but diffuses away in soil water
-Urea, nucleic acids, etc.
Diffuse through body wall
Voided through intestine, excretory system
Stored in crystalline state
NEMATODE PHYSIOLOGY
EXCRETORY SYSTEM
Other Functions
-Osmoregulation
-Removing excess water
-Regulating turgor in body cavity
-General “cleanup”, removes foreign particles
-Releases enzyme-containing secretions
a) Exodigestive enzymes
b) Protective coatings
c) Assist molting
No Circulatory System
No Respiratory System
Circulatory and respiratory processes
are accomplished by movement of
fluids within the body cavity.
NEMATODE PHYSIOLOGY
RESPIRATION
Nematodes are aerobic organisms
-Require oxygen for metabolism
-Thin shape and semipermeable cuticle
-Width of nematode restricted by diffusion
-Oxygen availability and demand depend on:
1) O2 concentration in environment
2) Diffusion of O2 into microsite
3) Metabolic demand from
body size, activity, temperature, starvation
NEMATODE PHYSIOLOGY
RESPIRATION
When oxygen is insufficient, nematodes
-Decrease rate of development
-Stop moving
-Enter cryptobiosis
NEMATODE PHYSIOLOGY
RESPIRATION
Many nematodes are facultative anaerobes
-Persist through microaerobic (<5% O2)
and anaerobic (no O2) periods
with fermentative metabolism of glycogen
Caenorhabditis survived 0% O2 for 80 hours
Aphelenchus survived >30 days!
NEMATODE PHYSIOLOGY
RESPIRATION
Oxidative metabolism preferred
1) More energy produced
2) Toxic waste products produced from
fermentative metabolism
O2 uptake is reduced as O2 levels decline from
normal air (21%) to 5%.
At <5% O2, O2 uptake stops and nematodes
must switch to fermentative metabolism
NEMATODE PHYSIOLOGY
MOLTING
As nematodes grow they need to shed their
cuticle to increase in size.
Nematodes generally go through 4 molts.
J1 J2 J3 J4 Adult
Timing of molting depends on “stage of
development”(physiological age), not necessarily
chronological age, so each stage tends to be a
certain size for a given species.
NEMATODE PHYSIOLOGY
MOLTING
Just before molting begins, the
nematode stops feeding and
becomes sluggish or inactive.
A = Normal cuticle.
B = Initial stages of molting,
the hypodermis thickens
C = Hypodermis secretes new
cuticle under the old one
NEMATODE PHYSIOLOGY
MOLTING
D = Two cuticles separate and a
space develops between them.
Folds may appear in the old
cuticle as it enlarges and
becomes loose.
E = Most of the old cuticle is
reabsorbed before it is shed.
F = The old external cortex is
not reabsorbed and is the only
part of the cuticle cast off.
NEMATODE PHYSIOLOGY
MOLTING
The nematode breaks out of the old cuticle by
"rubbing" against soil particles.
New cuticle is convoluted to allow for rapid
growth, increase in thickness.
The entire cuticle is shed including the lining
of the stoma, esophagus, vulva, cloaca, &
rectum.
New cuticular structures are formed.
The basal part of the old stylet dissolves and slow
retractile movements disengage the head from the
anterior part of the old stylet, which remains
attached to the anterior part of the old cuticle.
R.S. Hussey
NEMATODE PHYSIOLOGY
SENESCENCE, QUIESCENCE & CRYPTOBIOSIS
Normal life spans for
most individuals of a
given species are similar.
Normal aging process:
= Senescence
NEMATODE PHYSIOLOGY
SENESCENCE, QUIESCENCE & CRYPTOBIOSIS
When environment shifts unfavorably
nematodes experience metabolic “slowdown”
= Quiescence
Movement slows or stops, life cycle
development delayed.
Metabolism slowed, but still detectable.
NEMATODE PHYSIOLOGY
SENESCENCE, QUIESCENCE & CRYPTOBIOSIS
Increased or prolonged environmental stress
leads to metabolic “shutdown”
= Cryptobiosis
Metabolism is not detectable!
NEMATODE PHYSIOLOGY
SENESCENCE, QUIESCENCE & CRYPTOBIOSIS
Physiological aging slows in quiescent nematodes.
64-day-old quiescent Meloidogyne javanica = physiological age of 4 days.
128-day-old Tylenchulus semipenetrans had aged 16 days.
Aphelenchus avenae under O2 stress for 90 days had not aged at all.
NEMATODE PHYSIOLOGY
SENESCENCE, QUIESCENCE & CRYPTOBIOSIS
Several environmental conditions may induce nematodes
to enter a quiescent or cryptobiotic state.
Anhydrobiosis = condition due to lack of water.
Cryobiosis = caused by lowering of temperature.
Anoxybiosis = absence or low levels of oxygen.
Osmobiosis = removal of water from organisms by a
solution that has high osmotic potential.
Several may occur a same time.
Anhydrobiosis most common.
NEMATODE PHYSIOLOGY
SENESCENCE, QUIESCENCE & CRYPTOBIOSIS
Induction of anhydrobiosis due to slow
dehydration includes physical and physiological
responses to resist desiccation.
Physical response = coiling into a spiral reduces
the surface area exposed to the environment
and reduces the rate of water loss.
When dried straight, nematodes have little
control of water loss, lose water too quickly.
Aphelenchus avenae in anhyrobiosis
Coiling = physical response
M.A. McClure
NEMATODE PHYSIOLOGY
SENESCENCE, QUIESCENCE & CRYPTOBIOSIS
Some nematodes swarm into a mass that also
helps protect them from rapid water loss.
At times, a lipid layer surrounding the cuticle
causes the swarm to clump and stick together
(= nematode wool).
Nematodes inside plant tissues are further
protected.
Swarm of Anquina tritici juveniles
in anhydrobiotic state
M.A. McClure
Ditylenchus dipsaci J4 – nematode wool on basal plate
defra
defra
NEMATODE PHYSIOLOGY
SENESCENCE, QUIESCENCE & CRYPTOBIOSIS
Physiological Responses – 1. Water Dynamics
Active nematode = 75-80% water.
Anhydrobiotic in dry air (0% rh) is 2-5% water.
Water lost by dehydration (80% -> 5%) is
"free water" = used in metabolic processes and
in cytoplasm. Can be lost without cell damage.
The 2-5% water remaining is "bound water"
and is essential for the maintenance of
membranes and other structural components.
NEMATODE PHYSIOLOGY
SENESCENCE, QUIESCENCE & CRYPTOBIOSIS
Physiological Responses – 2. Metabolic Changes
During dehydration
- lipid concentration decreases
- trehalose (a non-reducing sugar) increases 7X
- glycerol concentration increases substantially
Glycerol replaces bound water in stabilizing
membrane structure.
"Quick dried" nematodes do not synthesize
glycerol, membranes destabilize, and nematode
dies.
NEMATODE PHYSIOLOGY
SENESCENCE, QUIESCENCE & CRYPTOBIOSIS
Resistance to Unfavorable Conditions
Cryptobiotic = resistant to harsh environment
Don’t want conditions that would induce
cryptobiosis before you treat!
Examples:
See Handout
NEMATODE PHYSIOLOGY
RESISTANT STAGES
In some nematodes only one life stage from egg
to adult is resistant. Can be any stage.
See handout for examples
In other species, any stage from the J2 to adult
can successfully enter and exit cryptobiosis.
NEMATODE PHYSIOLOGY
RESISTANT STAGES
Another form of resistance strategy is called the
dauer juvenile (= dauer larvae).
The third stage juvenile retains the second stage
cuticle = double cuticle. Common among
bacterial feeders.
The body is usually thinner, cuticle thicker, and
nematode does not feed.
This stage is often used during migration.
NEMATODE PHYSIOLOGY
NEMATODE LONGEVITY
Nematodes can persist in a resistant state
for many years.
Normal life spans of active nematodes
Caenorhabditis = 4 days
Xiphinema = 3 years
Most plant parasites ≈ 35 days
Longer if cooler, shorter if warmer.
Longevity is more an expression of
physiological state than of time.