Feeding

Question 1

What is digestion?

Answer 1

All metazoan and heterotrophic protists must locate, select, capture, ingest, digest and assimilate food
Site of digestion – either extracorporeally (outside the body), intracorporeally (in a gut chamber of some sort), intracellularly (within a cell)

Question 2

The gut

Answer 2

Metazoans generally have a gut i.e. an internal digestive tract or alimentary canal. Not all do!
Some have only one opening, this is called an incomplete or blind gut e.g. platyhelminths or cnidaria
Most others have a through or complete gut allowing for a one-way flow of food/excreta. This implies the presence of a mouth and anus.

Question 3

What are the feeding modes?

Answer 3

Heterotrophic feeding modes are highly diverse and can be organized according to many different classifications:

Habitat type: freshwater, sea or land

What organisms eat: herbivores, carnivores, omnivores, detritivores

Feeding method: browsing, suspension/filter feeding, deposit feeding, etc

Food size: microphages (feeding on very small organisms) versus macrophages

Food location within the environment: water column, benthic substratum, etc

Question 4

What are the different types of feeding modes?

Answer 4

1. Browsers
2. Suspension feeders
3. Deposit feeders
4. Active predators
5. Biters, chewers, suckers.

Question 5

How to browsers feed?

Answer 5

Herbivores, e.g. Molluscs such as snails and chitons
They have a rasping radula (ribbon-like structure or belt-like rasp armed with chitinous teeth) that removes the layer of encrusting organisms (algae) from rocks
Found in the mouths of all molluscs except bivalves
It consists of minute chitinous teeth that are continuously produced to replace old ones

Question 6

How do suspension feeders feed?

Answer 6

They remove suspended food particles (floating or drifting) in the water by some sort of capture, trapping or filtration mechanism.
Particles can be large and visible or microscopic.
For example: sponges, ascidians, brachiopods, bivalves, many crustaceans, polychaetes and gastropods.
Typically, three basic steps:
transport of water past the feeding structures removal of particles from the water transport of the particles to the mouth.
Some have efficient filtering mechanisms.
Main food selection is based on particle size.

Question 7

What strategies exist to capture food particles?

Answer 7

• Move part of/whole body through water (active)
• Water moved over feeding structures (passive)
• Facultative mode or combination of both above

Question 8

What is passive food particle capturing?

Answer 8

spend little energy to get water in, but lots of energy to capture food (e.g. stinging cells)

Strategy: Optimal positioning in the environment where they can use the water flow.

Question 9

What is active food particle capturing?

Answer 9

spend lots of energy to transport water over filtration surface

Strategy: alter the flow, filter large amounts of water

Question 10

What are the 4 primary mechanisms of suspsension feeders?

Answer 10

1. Motile setal-net feeders (setose appendages)
2. Mucous-bag feeding (mucous net, trap)
3. Ciliary-mucous mechanism
4. Tentacle/Tube feet suspension feeding.

Question 11

What are setose appendages?

Answer 11

Coarse particles are trapped (setae not as fine as cilia, no mucus) and moved to mouth

E.g: larger planktonic and benthic crustaceans.

Question 12

What is mucous bag feeding?

Answer 12

Nets or bags of mucus are spun from the mouth.
When the trap is full, both the mucus and the prey are eaten.
The net can be filled by water flow provided by muscular means or natural currents.
eg. Annelid worms.

Question 13

What is cilliary mechanism?

Answer 13

Numerous slender filaments
Particles can be trapped by mucus or not.
The beats of the cilia produce a current and can direct the stream of trapped particles
Sorting on basis of both particle size and chemosensing.
eg. bryozoans.

Question 14

What is tentacle or tube feed suspension feeding?

Answer 14

Tentacle-like structures capture food particles, with or without mucus
For example: Echinoderms (e.g. brittle stars and crinoids) and cnidarians (certain sea anemones and corals).

Question 15

What are deposit feeders?

Answer 15

Obtain nutrients from sediments of soft-bottom habitat (mud and sand) or terrestrial soil.

Direct deposit feeders: swallow large amounts of sediment (polychaete annelids, some snails, sea urchins and most earthworms).
Selective deposit feeders: Uses tentacles preferentially remove uppermost deposits from sediment.

MIcro algea is in the top layer of soil, where the most sunlight is reci

Lecture 7 slide 17 figure

Question 16

What is active predation?

Answer 16

Active predation is associated with active capture of animals
Active predation requires: prey location, pursuit, capture, handling and ingestion.
Prey location requires a certain level of nervous system sophistication in which specialized sense organs are needed.
Chemosensory location of prey: Contact chemoreception (e.g. antennae, legs of insects; cilia in marine invertebrates)
Visual orientation
Vibration detection

Most invertebrates have sensory receptors (gustatory and olfactory) in the head region, but some organisms have chemoreceptors around their bodies (e.g. jellyfish which are radially symmetrical carnivores) or on their legs and other body parts (e.g. insects and crustaceans).

Question 17

What can predators be classified as?

Answer 17

Motile stalkers
Lurking (ambush) predators
Grazing carnivores
Cannibalistic

Question 18

What are motile stalkers?

Answer 18

Actively pursue their prey
Chemosensation is highly important to locate prey
E.g. ciliate protists, nemerteans, polychaete worms, gastropods, octopuses, squids, crabs, seastars

Question 19

What are lurking predators?

Answer 19

Sit-and-wait to locate prey
Many live in burrows or crevices from which they emerge to capture passing prey. They are often territorial and some spend substantial energy building prey traps.
E.g. mantis shrimp, spiders, some polychaetes, praying mantis.

Question 20

What are grazing carnivores?

Answer 20

Move on the substratum to feed on epifauna. Diet generally includes sessile or slow moving prey. They can be omnivorous (plant material + animal prey).
For example: shrimp, crabs, sea spiders, some snails.

Question 21

What are Cannibilistic predators?

Answer 21

Special category of carnivory. Mostly adults feeding on juveniles.
However, also includes matriphagy (juveniles eating their mother) and sexual cannibalism (females eating males).

Question 22

What are biting, chewing and sucking insects?

Answer 22

These modes are mostly found in insects that feed on plants:
Biters & chewers: need powerful mandibles (e.g. grasshoppers, leafcutter ants)
Sucking insects: modified mouthparts to feed on nectar or plant sap (e.g. butterflies, true bugs) or HUMANS (e.g. mosquitoes)

They can cause serious damage to man-made structures
Some can switch to carnivory if needed.

Question 23

feeding in terrestrial environemnts?

Answer 23

• no filter feeders
• browsers feed on vegetation
• deposit feeders live in soil
• gut flora have diversified to assit in invertebrate digestion.
• evolution of mouth parts to deal with perticular food sources.

Question 24

How are nutrients balanced?

Answer 24

Optimal performance and fitness requires nutrient levels (amino acids/proteins, carbohydrates, lipids) to be appropriately balanced. This is because:

• An imbalance can be energetically costly as the organism may have to keep eating to obtain enough of a rare component
• Nutrient excess can be toxic
• Conversion of carbohydrates to protein can be metabolically costly

in insects a balanced diet allows to acquire the optimal intake of all nutrients simultaneously.

Intake nutritional target can change with activity levels, development , reproduction or feeding mode.

Lecture 8 slide 6

Question 25

How do carnivorous insects feed?

Answer 25

require higher amino acid (protein) and lipid relative to carbohydrates (low digestibility of animal carbohydrates)

Question 26

How do herbivorous insects feed?

Answer 26

require amino acid = carbohydrates or, amino acid < carbohydrates (phloem-feeders). Phloem feeders are often associated with presence of symbiotic bacteria (to provide additional proteins which are not present in their food).

Question 27

What is a holometabolous species?

Answer 27

undergo complete metamorphosis: eggs, instars, pupae, adults
e.g. butterflies

Question 28

What is a hemimetabolous species?

Answer 28

There is no pupal stage; they go from eggs, instars to adults; wings develop externally
e.g. termites, locusts

Question 29

Plant eating insects

Answer 29

With symbionts - have a low P:C ration
Without symbionts - have a P:C ration close to 1.

Question 30

Carnivoires

Answer 30

e.g. species which feed as larvae on animal-based food: wasps, blowflies, moth caterpillars
- have a high P:C ratio

Question 31

How do we study feeding behaviour and diet?

Answer 31

1. Comparative physiology i.e. mouthparts and adaptations e.g. insect mouth types – what info do we get?
2. Lab and in situ observations
3. Food preference with food choice
4. Gut content analysis
5. Stable isotope analysis

Question 32

Comparative physiology - Insect mouth types.

Answer 32

There are 5 major insect mouth type functional groups.
Some examples:
Chewing= grasshopper
Piercing and sucking = mosquito
Siphoning = butterflies and moths
Sponging = house flies and fruit flies
Chewing and lapping = honeybees

Each of the mouth types reflect a specialization to a particular type or source of food. Siphoning (butterflies) and Piercing and sucking (mosquitoes) can feed on nectar and for the latter, mosquitoes can also feed on blood.

Question 33

Chewing insects have 4 distinct mouth parts:

Answer 33

Labrum
Mandible
Maxillae
Labium

Question 34

Food choice experiments

Answer 34

The authors presented individuals of Octopus tehuelchus with several food choices including crabs and bivalves.
These were placed within sight and out of sight (in the dark)
Seem to prefer crabs and also well-known that crabs provide optimum nutrition for octopuses.
Oysters were never chosen, some mussels were only eaten when there was no other choice
Evidence of chemical cue detection in feeding
Ethical considerations around keeping animals in labs and experimentation methods, does not account for other variables that may influence food choice..

Question 35

Gut content analysis?

Answer 35

Collected 5 male and 5 female individuals every 3 hours over a 24 hour period.
Frozen to stop metabolism and to euthanise
Guts removed and photosynthetic pigments measured to determine chlorophyll content AKA microphytobenthos (the main food source of fiddler crabs)
Gut content analysis shown in graph (b)
Males fed more actively than females
More feeding during daylight hours and no feeding at night
Confirmed by video footage (a)
Very invasive (and lethal of course), does not account for other food sources, not always easy to identify gut contents, only a snapshot.

Question 36

Stable isotope analysis?

Answer 36

Using rations of Carbon and Nitrogen isotopes from tissue
Determine an organism’s position relative to other organisms in a trophic web (Nitrogen decays as we move up the trophic web).
Determine the source of the food chain (Carbon decays as we move to more marine or C4 sources)
Based on the range of signatures – diet type and variability
Based on overlap of signatures – niche overlap within a system
Can be destructive if the whole organism is removed, only as reliable as data sources, doesn’t work well in extremely diverse habitats, best with complimentary gut content analysis.