Adaptations MT

Adaptations MT

1. Adaptation & optimisation

   • Paley framed problem of adaptation as need to explain observed fact that organisms appear to be designed
     • Origin of Species explained how natural selection could be responsible for apparent design of organisms
       • Fisher showed natural selection acts to increase mean fitness
         • Adaptation: the process of finding alternative trade-offs among conflicting performance objectives in organisms subject to similar constraint
         • Fisher's fundamental theorem of natural selection
           • Rate of increase in fitness of any organism at any time is equal to its genetic variance in fitness at that time OR rate of increase of fitness of any species is equal to its genetic variance in fitness
   • Two models of evolution
     • 1. Phyletic gradualism: most speciation is slow, uniform & gradual 2. Punctuated equilibrium: morphological stability followed by rare bursts of evo change via rapid cladogenesis - appropriate model for fossil record
   • Gould's aptive triangle
     • Gould’s aptive triangle depicts the ‘causes’ of traits as structural (physical), functional (adaptive) & historical (phylogenetic) Given trait is supposed to be located somewhere inside triangle according to relative importance of the three causes However as these represent logically distinct levels of explanation, it is unclear how they are supposed to interact   
   • Physical biomechanical constraints
     • Grandfather clocks
     • Brachiating gibbons
     • Inverted pendulum walking
     • Planar mass-spring model of running
   • Multi-objective optimisation: adaptation with selection driven by multiple conflicting performance criteria
     • Bird flight is an example
     • The Pareto set

2. Adaptations to the deep sea

   • Megafauna, macrofauna, meiofauna
   • Most deep-sea ecosystems rely on sinking of organic material
   • Trends in size depend on lifestyle
     • Changes in metabolic rate with depth of habitat reflect lifestyle
       • Visual interactions hypothesis
         • High light levels & limited refuges available in the epipelagic realm has resulted in selection for high locomotory capacity for predator-prey interactions amongst visually orientating taxa & that high metabolic rates follow
       • Changes in feeding mode of specific taxa with depth
         • Deep sea sponges Pennatulids Predatory tunicates
         • Shift from suspension feeding to deposit feeding/macrophagy
   • No sharks below 4000m depth: squalene
   • Adaptations to high pressure
     • 1. Homeoviscous adaptation
     • 2. Changing rigidity of biomolecules
     • 3. Organic osmolytes
   • TMAO content of animals increases with depth
   • Adaptations to hydrothermal vents
     •  Exiting of the vent fluid from the seafloor may form a buoyant plume arising from the seabed & an effluent layer or non-buoyant plume as it is entrained by the near-seabed currents These plumes are now used to locate hydrothermal vent fields Vent fluid may exit the seabed at temperatures of up to 407°C, are anoxic, generally have a low pH & contain toxic chemicals including hydrogen sulphide & heavy metals (depleted in Mg, P) The major stresses at hydrothermal vents are therefore high temperature and pressure, low oxygen & presence of toxic chemicals including heavy metals
     • 1. Symbiosis with sulphur bacteria
     • 2. Inhabited area: live at interface
     • 3. Hypoxia/anoxia
       • Increased gill surface area
         • Oxygen binding proteins
     • 4. High temperatures
       • Avoid them
         • Modify immediate environment
           • Induce molecular chaperones e.g. HSP70
     • 5. Toxicity - sulphides & metals
       • Metallothionein genes

3. Adaptations to low light

   • Change in spectral comp of light with depth
     • In the ocean the red end of the spectrum is absorbed preferentially In clear ocean waters light at depth is predominantly in blue-green wavelengths In coastal waters organic particles change the spectral composition of light so the water can look yellow / green   
   • Pelagic life
     • Zooplankton Nekton Micronekton
   • Diurnal vertical migration
     • Largest migration on Earth Many mesopelagic animals migrate up towards ocean surface at dusk & feed in shallower water layers, migrating to greater depth at dawn or when they become satiated with food
     • Mechanisms used by organisms to time & synchronise their migrations
       • 1. Light intensity (-vely phototactic in high light, +ve phototaxis in low light) 2. Internal (circadian) rhythm  3. Temperature
       • Why does DVM occur?
         • 1. Predation  2. Maintaining station 3. Energetic reasons 
   • Limited food in the twilight zone
     • Poor efficiency of marine food webs Large-scale recycling & consumption of organic material in epipelagic zone
     • Filter feeder abundance varies in the ocean
       • Thrive in surface waters because of abundance of small organisms from bacteria to large diatoms Energetically demanding - few in deep water
   • Predators adapted to deep sea
     • - Relative proportion of predators increases in many parts of the ocean to up to 3000m depth - Once predators make contact with prey it is very important to be able to capture it & swallow it - Many deep-sea fish have developed enormous teeth relative to their body size as well as a gape & stomach size that allow them to swallow & digest extremely large food particles - Examples: melanocetid angler fish + black swallower Chiasmodon - Some fish have enormously flexible jaws that can almost be disarticulated to ingest prey much bigger than themselves (e.g. dragon fish and viperfish of the Stomiidae)   
   • Light changes at dusk & at night
     • - During day, light is bright with a full spectrum of sunlight - Dusk, however, can see a marked shift in the spectral composition of light to become dominated by blue & violet wavelengths - Night light varies greatly with the presence or absence of the moon - Full moonlight has the same spectral composition as sunlight but the light is a million times dimmer - Starlight on a cloudless night will provide light about 108 times dimmer than sunlight, a cloudy night may be 100 times dimmer than this
   • Why are terrestrial species nocturnal?
     • 1. Avoidance of visual predators 2. Avoidance of competition 3. Hunting or foraging may be more successful at night 4. Avoidance of hostile environmental conditions 
     • Eyes have adapted to the dark
       • Become larger! Types of eyes that can be found in deep sea animals (and other animals)...
       • Camera eye
       • Reflector eye
       • Apposition compound eye
       • Superposition compound eye
       • Typical vs. tubular camera eyes
         • - Typical eyes are positioned laterally on the head - Tubular eyes may be positioned to look upwards or forwards - Typical eyes have a large field of view but a restricted binocular overlap - Tubular eyes have large spherical lenses, focus sharp image on retina, have good coverage of small field, very sensitive as full diameter of lens exposed for light capture but very restricted field of vision so could miss potential prey/predators → to counteract this problem deep-sea fish with tubular eyes have developed a number of modifications to improve the visual field including development of secondary accessory retina lining the wall of the tubular eye  - 2 examples of deep sea organisms with tubular eyes: Opisthoproctus - upward pointing eyes to detect silhouettes in downwelling light; Gigantura chuni – eyes point forward, binocular vision excellent for judging distance  
       • Tapetum
         • - Many deep-sea fish have a reflective layer or tapetum lucidum - Reflects light back through retina allowing a second chance for light absorption - Wavelength of reflected light is in UV-green spectrum, peaking in blue  
       • Some deep sea fish adapted to low light with no. of rods in retinas
       • Absorption of retinal pigments
   • Bioluminescence
     • Production of light by a biochemical reaction in an organism Produced by oxidation of light-emitting luciferin
     • Can be used for defence...
       • 1. Startle predators 2. Obscure prey 3. Prey sacrificing a bioluminescent part of the body 4. Burglar alarm 5. Warning display 6. Camouflage
       • Can be used to lure prey, illuminate prey or confuse prey
   • Camouflage used by deep sea fish
     • 1. Cryptic colouration 2. Silvering3. Transparency 4. Counter-illumination 
     • Has led to counter adaptations
   • Other adaptations to life in the dark
     • Long appendages
       • Echolocation
         • Sound

4. Adaptations to diving

   • Diving is largely a feature of animals that are air breathing that need to dive under water to obtain food in water, but occasionally used for travel Diving occurs across the animal kingdom, but common in seabirds & especially common across a range of mammalian taxa Predaceous diving beetle preys on organisms ranging from other insects to fish larger than themselves
   • Morphological adaptations to diving
     • 1. Body streamlining 2. Limb reduction and modification 3. Tail modification 4. Increase in size
   • Basal mammalian dive response
     • Experienced in all mammals including humans Best developed in diving mammals Adaptation to conserve intrinsic oxygen stores
     • 1. Apnea (breath holding)
       • 2. Bradycardia (slowing heart rate)
         • 3. Vasoconstriction (perfuses extremities with less blood)
   • Aerobic Dive Limit
     • Depends on intrinsic oxygen stores (size)  Found in blood and muscle
   • Functions of lung collapse
     • 1. Stores oxygen as when lungs reinflate on ascent from dive, oxygen in them is released into blood 2. Reduces absorption of nitrogen gas stored in lungs (decompression sickness) - if ascent rate too fast then nitrogen forms bubbles in tissues & blood supply 3. Acts as pulmonary shunt closing off part of blood system to help reduce oxygen use
     • Avoids decompression sickness
       • Animals can suffer from diving problems
         • 1. Deep-diving animals lose nitrogen at shallow depths from tissue to lungs 2. Mass-stranding of deep-diving whales associated with mid-frequency active sonar 3. Decompression sickness can occur as a result of bycatch 4. Evidence of dysbaric osteonecrosis in sperm whale
   • Myoglobin
     • Most consistent hallmark of elite animal divers Mb increases oxygen reserves for aerobic metabolic activity in muscles Deoxygenated Mb acts as nitrate reductase converting nitrate to NO; down-regulates mt respiration, reducing oxygen consumption Maximum dive time of diving mammals is significantly correlated with size of species & maximum myoglobin conc. in muscle
   • Gliding is a behavioural adaptation to diving
     • +ve and -ve buoyancy
   • Body mass & myoglobin conc. are the biggest predictors of diving ability

5. Adaptations to extreme cold

   • Problems with low temperature
     • 1. Body function 2. Freezing 3. Slow-physiological rates 4. Metabolic scope 5. Locomotory activity, chill coma
   • Depauperate terrestrial fauna in Antarctica
     • - Dry Valleys of Victoria Land & nunataks of Ellsworth Land amongst the simplest ecosystems on Earth - Fauna of springtails, mites, tardigrades, nematodes, rotifers, flightless midges - Endemism about 58% (evidence of survival of glaciations in refugia) - Incredibly harsh environment (down to -90°C, ice, lack of water, exposure to UV, extreme temperature variation) - Only 0.3% of 14 million km2 is ice-free   
     • Low plant diversity
       • Only two species of flowering plants – Deschampsia antarctica & Colobanthus quitensis Mosses (many occur outside Antarctic) Lichens (some likely to have survived recent glaciations in refugia) Microflora (some endolithic)   
       • Diverse & endemic marine community
         • Reminiscent of the Palaeozoic Fauna lacks durophagous (shell-breaking) predators, especially decapod crustaceans such as brachyuran crabs or lobsters, also balanomorph barnacles and sharks missing Low diversity of other groups (caridean shrimps, molluscs etc)
         • Terrestrial vs marine environment
           • - Environment fundamentally different - Diurnal & seasonal variability - Terrestrial environment selects for: disproportionate response to small increment; compensation at low temperatures - No such selection pressure in marine environment - (Alternatively, are terrestrial studies misinterpreted? O2 needs associated with other body processes, not temperature directly
           • Vertebrate life is big, plant & invertebrate terrestrial life is small
         • Why did true crabs and lobsters die out?
           • Many durophagous predators (true crabs and lobsters) disappeared in the Eocene / Oligocene boundary, some survived into Miocene but disappeared as climatic conditions deteriorated further This may relate to their ability to regulate magnesium Appears that haemolymph magnesium concentration in the blood has a direct effect on neuromuscular function At low magnesium concentrations, these animals have higher activity levels & so ability to down regulate haemolymph magnesium concentrations at low temperatures can compensate for decreased heart rate and ventilation of the gills For species that are poor regulators of magnesium low temperatures lead to depressed heart rates & gill ventilation & animals move into anaerobic respiration & eventually die if stressful conditions remain, or worsen Quite surprising given that oxygen concentrations increase with decreasing seawater & some scientists think that poor magnesium regulation does not fully explain the lack of crabs & lobsters in Antarctic waters   
         • Notothenoid fish
           • Mode of action of antifreeze glycoproteins:  AFP orders water at active site due to hydrogen bondsWhen AFP comes into close proximity with the ice/water interface, ice formation is promoted & ice binds the proteinProtein disrupts ice further ice formation, halting crystal growthEvolution of notothenoid antifreeze:  AFPG evolved from a pancreatic trypsinogen geneAFGP still synthesised in pancreas, released into gut & reabsorbed & distributed in blood serumFood is a likely source of ice crystals – digestive enzyme makes senseExample of Escape from Adaptive Conflict (EAC) by gene duplication, conflict being between function of trypsinogen as digestive enzyme & as an AFP
         • Ice fish have lost haemoglobin
   • High levels of oxygen and gigantism
     • Some Antarctic invertebrates such as isopods, amphipods and pycnogonids are giants compared to temperate / tropical relatives Thought to be because high concentrations of oxygen in low temperature seawater leads to high oxygen uptake across respiratory surfaces & increased oxygen concentration in the circulatory fluids, increasing the path length of the respiratory system & allowing for larger body-sizes in invertebrates that exchange respiratory gases across their external surfaces
   • Characteristics of terrestrial ecosystems
     • 1. Extreme cold 2. Unavailability of water (dessication)  3. Ice 4. Exposure to high UVb
     • Penguins have adapted to Antarctic terrestrial environment
       • High density feathers & large layer of subcutaneous fat are impervious to winds Emperor penguins with large chicks will hatch at end of winter/start of spring Chick independency is linked with krill availability Maintain extremities just above freezing, ice more dense than air so is colder Emperor & King penguins huddle = disruption of Allee effect Use countershading to avoid predators from above and below Make nest of rocks to avoid water   
     • Avoiding exposure or gaining protection from UV radiation
       • 1. Avoidance: Cryptoendoliths live inside rocks where geology permits Alternatively species can live under rocks (hypolithic) or in cracks (chasmoendolithic) A 500μm cover of soil can confer complete protection from UV 2. Protection: Plants have evolved UV screening pigments (protectants) e.g. upregulate flavonoids which confer UV protection   
     • Some animals are freeze tolerant
       • Most microarthropods survive low temp. by supercooling
         • Anhydrobiosis: metabolism ceases
     • Dehydration is highly stressful
       • Desiccation and cold tolerance are similar
         • 1. Problems at the cellular level Solute concentration pH changes  Physical shrinkage Membrane damage 2. Biochemical similarities "Cryoprotectants" also limit desiccation Seasonal production fits with drying Produced in temperate and tropical spp Desiccation features preadapt for cold?   
   • Climate change & Antarctic organisms
     • Special case of tropical reef-forming corals –coelenterate with endosymbiotic alga – which already function close to upper thermal limit BUT, upper limits may occur at very low temperatures Problems of metabolic scope given low BMR Compound with strong stenothermy (ability to tolerate only small range of temp.) e.g. burying, righting in Antarctic marine invertebrates (molluscs, starfish) Compound further with some activities being v. inefficient at low temps (e.g. RNA and protein synthesis), increases costs Max activity can be very limited  Climate change...Many Antarctic marine species are stenothermalMarine invasives may have an advantage