Adaptations to low food

Question 1

The key to surviving in low food environments is energy management.

Answer 1

1) Maximise energy input: behavioural and morphological adaptations to get it first.
2) Efficiency in digestion, metabolic conversion: the ability to turn your food into lipids, carbohydrates and amino acids.
3) Limit expenditure of energy gained: behavioural adaptations to limit energy usage.

Question 2

Benthic systems feeding strategies

Answer 2

Predation

Filter feeding

Deposit feeding

Scavenging

Question 3

Filter feeders

Filter feeders feed by straining or filtering suspended matter and food particles from water, typically by passing the water over a specialized filtering structure.

What is this strategy used by?

Answer 3

This strategy is utilised by clams, krill, sea lilies, jellyfish, sponges, baleen whales and many fish (including some sharks).

Question 4

What are the strategies of filter feeding?

Answer 4

Generally there are two methods:

1 – Move through water containing suspended particles (e.g. basking shark).

2 – Remain static and filter particles as they flow past (e.g. Crinoid).

Question 5

DEposit feeders

Deposit feeders are also known as detritophages or detritivores.

They obtain nutrients by consuming detritus which is decomposing plant (e.g. dead phytoplankton) and animal parts (e.g. “messy-eating”) as well as organic faecal matter.

What strategies are there for deposit feeding?

Answer 5

Deposit feeders feed on or near the seafloor (the benthos), often simply removing labile organic matter from the sediment.

This can de done in two ways:

1) eat the sediment, digest the nutrients and pass the sediment (e.g. sea cucumbers);
2) eat sediment, filter nutrients and blow sediment out through gills (fish).

Question 6

Deposit feeders can partition resources depending on their morphological characteristics and behaviour.

Give some examples of how this is done

Answer 6

• In holothurians, morphological differences are important because it is a combination of tentacle structure, body wall consistency and body extension.
• Mobility can differ depending on buoyancy and swimming capabilities.
• The type of gut also varies among species which allows differences in digestive capabilities.
• These differences in form and function lead to different species begin surface deposit feeders or subsurface deposit feeders.

Question 7

The search for a dead animal (often referred to as ‘food-fall’ or ‘carrion-fall’), starts with the odour plume emanating from the source.

Answer 7

• Odour plume is generated by oils (e.g. lipids and fats) which disperse from the dead animal as it breaks down.
• Long range detection of the plume is achieved through olfaction, and once detected, followed up-current to the source.
• The strategy lies in what the scavenger does prior to the odour detection.

Question 8

The three options are passive drifting, cross-current and sit and wait.

What energy demands are these strategies balancing?

Answer 8

• Passive drift is all about balancing energy between drifting down current and swimming back up current.
• Cross-current requires the largest energy expenditure but the most likely to intercept an odour plume quickly.
• Sit and wait requires the least amount of energy expenditure but the least likely to identify a source.
• Most scavengers will adopt the cross-current strategy because the highest probability they will find carrion.
  
  • As odour plume moves away from a food source it expands
  • Spreads like a meander – detecting it still requires a lot of effort from the animal

Question 9

What senses are required for short-range detection?

Answer 9

Other senses are required for short range detection rather than just olfaction which is used for long range detection.

Short range detection to localise the food source is important so the animal can begin to find it and consume it.

Touch, taste, hydrodynamic stimuli, noise and potentially sight are all important.

Question 10

Why do scavengers get bigger with depth and non-scavengers stay the same size?

Answer 10

Non-scavengers potentially have low energy but available food sources so do not need increase body reserves.

Scavengers food sources are unpredictable so need to maintain energy reserves by increasing body size but also be able to compete when they locate food.

Lower density but higher mass.

Question 11

Alan Jamieson paper - optimal foraging theory eels

Answer 11

• S. kaupii arrive at bait but are powerless to access the soft white muscle of a carrion fall until the dogfish Centroscymnus coelolepis arrives are tears it open.
• The time between the first bait bite (FBB) and the peak number of eels is linear.
• These two species co-exist but it is still unclear how related this is.
• For S. kaupii, it a behavioural adaptation to get to the bait first and then wait.

Question 12

How does the most effective feeding strategy change with depth?

Answer 12

• After 5000 m predation then begins to rise.
• This rise coincides with high abundances of lipid rich amphipods but also a change in a body structure (e.g. low muscle mass, hydrodynamic gel, reduced skeleton, etc…).
• Power to break up food source extra energy needed to adapt to the pressure – gelatinous underskin – hard to move

Question 13

What must a scavenger be able to do to survive in the deep sea (amphipod)?

Answer 13

(1) localize and recognize potential food sources,
(2) Be able to feed on large muscular food sources,
(3) Consume large quantities of food short periods of time,
(4) Store energy for utilization over extended periods,
(5) Supplement their diet with alternative food sources.

Question 14

What adaptations do amphipods have to localise and recognising food?

Answer 14

Amphipods sweep water over the proximal part of the antennulae, mouthparts and into the branchial region when beating their pleopods, to increase the chance of detecting chemical stimuli.

They also have a dense array of chemosensortype setae on the ventral side of the first flagellar article of the antennae.

They have short and stout antennae which are kept depressed to increase exposure to chemosensory stimuli.

These sensors are prominently exposed to the body of water through which the amphipod swims.

Question 15

What adaptations do amphipods have to feed on large muscular food sources?

Answer 15

• Amphipods often strip carcasses of every visible shred of flesh within 24 hours, and often when no other taxa are present.
• They have highly adapted mouth morphology.
• The right incisor slides in behind the left and the ‘shape’ of the bite is bowl-shaped.
• This allows these amphipods to remove larger pieces of food than other shallower water species which have a flattened mandible.
• The mouth is designed to fit as much food in as possible in the shortest period of time.

Question 16

What adaptations do amphipods have to selectively feed?

Answer 16

• Amphipods can characterize the food source using gustatory seta on the gnathopods and periods.
• The majority of gustatory sensors are found on the ventral margins of appendages thought to be used for ‘tasting’ food items.
• Thus discriminating between food items that differ either chemically or texturally.
• Evidence of selective feeding on liver and gonads during necrophagy presumably to maximize their energetic intake per unit feeding by consuming the most energy-rich tissues first.

Question 17

What adaptations to amphipods have to consuming large quantities of food quickly?

Answer 17

Amphipods have distinctively shaped molars that when closed form an almost complete funnel from the mouth to the stomach.

This to aid in guiding larger food particles to the digestive tract.

The alimentary tracts are adapted for the accumulation and storage of large volumes of food relative to their size.

Some can extend body wall ventrally to 2-3 times its body size.

Food can be stored in the midgut which can expand to fill the entire body cavity.

Not so good for brooding females.

Gauging themselves – underside opens up, hels in by a tendon

Females can’t gauge when they are brooding eggs

Question 18

What adaptations do amphipods have to store energy between infrequent feeds?

Answer 18

After gorging themselves they are likely to have to undergo an extended period without food before the next event.

There are two strategies to cope with this scenario.

(1) energy management; making the most of the last meal. Some necrophagous deep-sea amphipods may drastically reduce their metabolic activity during starvation periods.
(2) energy storage: some amphipods can survive without any food for 4 to 6 weeks in laboratory conditions.

Many have appreciable stores of lipids in their bodies (>25% of the total dry weight).

Presumably, an energy cache to cope with potentially long periods of starvation.

Question 19

Amphipod adaptations to supplemented diet?

Answer 19

• Another strategy is to supplement scavenging with other smaller food items, beyond the limits of necrophagy.
• The nutritional strategies of many amphipod species show a remarkable trophic plasticity in that supplementary to necrophagy.
• They exhibited detrivory and predation and even cannibalism.
• A more recent study showed that some extremely deep sea species possess a unique digestive enzyme capable of digesting wood debris, most likely in particulate form.

Question 20

Summary

Answer 20

Summary

Low food availability in the benthic environment.

Focused on 3 important feeding strategies or guilds- deposit feeders, predators and scavengers.

Examined the relationship in body size with depth in predators and scavengers.

Behavioural and morphological adaptations to finding and consuming food.