Temperature, desiccation and exposue Flashcards
Coping with temperature change and desiccation - what three methods do organisms use? Method A
A. Behavioural adaptations: settlement, hiding and migration
- Migrations – up and down the shore rather than hiding.
- Settle – close to adults? Away to avoid competition?
- Juveniles develop lower on the shore.
- Sucsessional development of larval settlement.
- Molluscs can lower their body temperature by around 20 degrees simply by hiding in a crevasse.
- Availability of crevasses for animals to hide in can determine the carrying capacity of that habitat.
- Evaporative cooling a particularly widespread strategy for gastropods.
- Trade-off with water loss – useful on the mid-shore.
- High-shore gastropod (probs may close off to keep the water)
- Mid-shore gastropods keep their foot extended.
- Some isopods use this tactic too
Coping with temperature change and desiccation
method B
B. Physical adaptations: advantages of shells
- External carapaces help but shells are the most efficient
- Operculum’s can be used to reduce water loss – but shells can also reduce overheating
- HOWEVER - no exchange with the outside environment waste/feed/ respire
- •Orientation of shell is also important – Littorina aspera in Panama points it’s spire upwards reduced heat absorbed from the sun (Garrity, 1984)
- •Colour – many tropical littorinids have very light-coloured shells
- Mucous can provide a layer of protection between the gastropod and rock surface.
- Ridges and tubercules increase surface area – re-radiate heat
- Tissues can be ±5oC different than rock surface
- Again we can see a difference between mid-shore and high shore species
HIGH – close operculum, light coloured shells
MID – foot extended, darker shells
Coping with temperature change and desiccation method C
C. Physiological adaptations: preventing water loss while still breathing
A ‘closed-box’ approach to water loss is a difficult compromise
How to maintain the right amount of water whilst allowing access to air for gas exchange?
- The respiratory organs
- Excretory systems
- Oxygen demand
C. Physiological adaptations: preventing water loss while still breathing
- The respiratory organs
- Tucked away in the body so water loss can be controlled
- Gills are often reduced in size or replaced by vascularised epithelia that function as lungs. Reduced surface areas helps reduce water loss.
- High-shore littorinids have reduced gills and much of the O2 uptake occurs across the mantle surface i.e. Melarhaphe neritoides. Absorb oxygen through skin.
- Many mid to low-shore species will actually take up as much O2 from the air as they do when underwater!
- Mechanisms employed in air are very efficient (helped by there being more O2 in a given volume of air than in the same volume of seawater)
- This is exploited by many species
- Barnacles – replace the water within their mantle cavity with an air bubble
- Siphonariid limpets – fill the front of their mantle cavity with air and use it as a lung in addition to gills
- Strongylocentrus purpuratus – this low-shore sea urchin takes air into its gut during emersion forming a facultative ‘lung’
Coping with temperature change and desiccation
- Excretory systems
- Replenishing water during emersion is difficult – some gastropods carry ‘spare’ water with them but this can soon be used up
- Kidneys of shore animals are well adapted for reabsorbing water from urine
- Gastropods produce copious urine through specialised cells in the heart wall called podocytes
- Cenchritis muricatus- podocytes replaced by minute tubules that allow lower rate of urine loss (Emson et al., 2002)
- Kidneys are also well adapted for storing excretory products for longer periods between infrequent opportunities for excretion
Coping with temperature change and desiccation
- Oxygen demand
- Many intertidal species adopt a state of inactivity during emersion
- Reduces demand for oxygen uptake and associated problems of water loss
- Mytilus edulis – valves close and heart rate drops, occasionally opening to allow an air bubble to be taken in.
- Over prolonged periods a reduced metabolism still demands more oxygen than is available so Mytilus can respire anaerobically
- High-shore animals have a problem - submergence may not occur for days or weeks.
- Littorinids enter a state of aestivation – metabolism vastly reduced conserving energy and water. Heart may stop beating and O2 uptake falls
- Cenchritis muricatus can survive without water for up to 18 months!!
Coping with temperature change and desiccation
Method D
D. Biochemical adaptations: desiccation tolerance, cold hardening and heat stress
- Intertidal plants and animals can tolerate a wide range of external (and internal) conditions
- Biochemical processes begin to shut down at the extremes of these tolerance ranges
- Fucus sp. will continue photosynthesising until they lose 60-75% of their water, it then ceases and resumes only when plants are rehydrated
Animals lose water - osmotic pressure rises dramatically
Cenchritis muricatus – sustain a weight loss of >20% but blood concentration rises to 2.5x that of seawater
Pacific limpet, Lottia scabra, can tolerate a 70% loss and blood concentration 3x that of seawater
how do these organisms respond to the rise in osmotic pressure associated with losing water?
In both these species the cells respond to increase in osmotic pressure by increasing free amino acid content
Amino acids are believed to form the basis of the tolerance mechanism as they allow osmotic pressure to rise without a rise in damaging ion content (Little, 1981)
Temperature tolerances often mirror the pattern seen for desiccation tolerances
Explain temperature tolerance and acclimation.
- •Mussels can survive extremely high temperatures if they have been briefly exposed to temperatures slightly higher than normal
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•The same applies to those that can tolerate freezing
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•Invertebrates may also produce some ‘antifreeze-like’ compounds that delay the onset of freezing – however this has so far only been found in one Antarctic species (Waller et al., 2006)
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•As we will see in detail with polar fishes the major mechanism limiting freezing damage is an ability to limit ice formation in extracellular regions
What are heat shock proteins?
- Many organisms produce ‘heat-shock’ proteins
- These are chaperone proteins which protect or restore heat-damaged proteins
- Mussels on high shore exposed to longer periods of stress and produce more proteins
- Temperature may not be the only cue: anaerobic conditions, change in osmotic pressure, blood pH/. Chaperone proteins give protection to things other than heat – heat just discovered first.
- Levels may vary between locations – microhabitat to km scales
Coping with waves and currents
A. Behavioural adaptations: hiding and living in the boundary layer
- Laminar flow – boundary layer (mm-cm)
Turbulent flow – thin veneer; viscous sublayer
Hiding in this layer or restricting attachment organs there is an important option for smaller organisms. Barnacles don’t grow to larger sizes in high velocity areas, staying within the thin veneer.
- Mobile organisms can hide in crevices – combined protection
Helicon pectunculus (SA) –lives in crevices on upper shore,
When prevented from returning after foraging 45% dies during the first high tide.
Coping with waves and currents
B. Physical adaptations: attachment, shape and size
- Sedentary animals have a variety of attachment mechanisms
Barnacles – membraneous or calcareous base glues to the rock
Mussels – Byssus threads attach individually
Byssus threads contain collagen proteins providing elasticity – mussels can move in the waves without becoming detached
Mussels can adjust the number and position of threads to account for the dominant direction and force of water flows
Benefits and disadvantages of living in beds
How do limpets minimise drag
Many organisms have evolved shapes that minimise drag forces and turbulence
Streamlining, gently curved outlines tapering downstream, ridges to deflect flow
