20-22: Locomotion Flashcards
Why must animals locomote?
Find food
Avoid becoming food
What is buoyancy?
An upwards force that opposes the weight of an immersed object
What does buoyancy force depend on?
Volume
An object is buoyant if it is less dense than water
Density =
Mass x volume
How seals overcome buoyancy
Exhale before diving to reduce buoyancy
They can remain submerged for over 20 mins
Blood contains more haemoglobin than us
Store oxygen in myoglobin
How diving birds overcome buoyancy
Compress their plumage
How jellyfish maintain neutral buoyancy
Do not possess well defined muscle tissue
Circular muscles are arranged as distinct bands on subumbrella surface
Contract/relax, causing bell to pulse
How siphonophores (hydrozoa) maintain buoyancy
Have swimming bells called nectophore
These contain mesogloea (mainly water)
It is used in jet propulsion
How does the Portuguese man o’ war maintain buoyancy?
Has a pneumatophore- a gas filled bladder and sail
This is filled with carbon monoxide from a gas gland
A siphon allows the gas to be expelled quickly, allowing it to be submerged
How do fish and invertebrates change body temperature in water?
Move up and down the water column- the higher in the column, the warmer and more buoyant they are
They cannot change their own because they are ectothermic
How do bathypelagic (1000-4000m depth) achieve neutral buoyancy?
Deposit wax esters in their tissues
What are wax esters?
Ester of fatty acid and fatty alcohol
Same chemical properties as triglycerides, but indigestible
Sperm whales’ use of lipid
Lipid contained in a large spermaceti organ in head
To descend, lipid cools until it solidifies
Increase in density makes whales able to sink without much downwards swimming
Calanoides actus (3mm long) use of lipid
Changes molecular structure of waxy esters
Makes them solid to induce sinking
What are open (Physostomous) swim bladders?
There is a connection (pneumatic duct) between the gas bladder and the esophagus
How do physostomous swim bladders work?
Gases for filling bladder are retrieved from the water surface
Pneumatic duct connects swim bladder to oesophagus
Eg. primitive ray-finned fish,-carp, catfish, eels
How do closed (Physoclistous) swim bladders work?
Found in ray-finned fish
The rete mirible fills the swim bladder via the gas gland with oxygen
Gas is reabsorbed by the oval as required
How do organisms stay stable when submerged?
Centre of gravity and centre of buoyancy should not be in the same place
When submerged, centre of gravity should be directly below the centre of buoyancy
How do organisms stay stable on the water surface?
Centre of gravity is above the centre of buoyancy
The centre of buoyancy moves as the body tilts
What is Reynolds number? (Re)
The flow around an organism depends on the intertial force/viscous force ratio (Re) of the fluid Low Re (<10) = no vortices generated High Re (>10) = vortices may be generated (if the object isn't streamlined)
Fluid flow at low Re
Inertia is negligible compared to drag
Fluid has no inertia so remains attached to objects’ surface- continues moving downstream
Streamlining is ineffectual as drag is dependent on surface area
Like moving through treacle
Fluid low at high Re
Inertia is more dominant
To prevent separation of the flow (drag), a body needs to be streamlined
Implications of a low Re for locomotion
When propulsion stops, motion stops
How do ostracods (seed shrimps) swim?
Use a second antennae
How do shrimps swim?
Use pleopods (swimming legs)
How do molluscs swim?
Jet propulsion
Jet is created by inflating the mantle cavity with water and then contracting it
The direction is dictated by the funnel
Eg. squid, scallops
What happens if an animal is denser than water?
It needs to generate lift which requires energy
What happens if an animals is less dense than water?
It will generate more drag due to its greater volume
At low speeds-
it is more economical to reduce density
At high speeds-
a more streamlined body and lift based on propulsion
Low speed teleosts feaures
Buoyancy and drag based propulsion
Have fins for rowing- move a volume of water, momentum
3 types of drag
Viscous drag
Pressure drag
Induced drag
What is viscous drag?
Parasite/skin friction drag
Caused by layers of fluid sticking to the object and to one another
It increases with speed
What is pressure drag?
Form/profile drag
Drag force due to inertia of the fluid- the resistance it has to being pushed to the side
Increases with speed
Depends on turbulence and shape
What is induced drag?
Consequence of producing lift
Decreases with speed
Depends on the the wing angle
What is labriform swimming?
2 types-
Drag-based pectoral fin swimming
Lift based pectoral fin swimming
What is drag-based pectoral fin swimming?
Has a power stroke and a recovery stroke- like rowing
What is lift-based pectoral fin swimming?
Has an abduction, adduction, and refraction
Depth control by sharks
Sharks are denser than water, so use their pectoral fins to generate lift
Some have metabolically inert squalene in their livers
Cartilage is lighter than bone
Drag reduction strategies
Streamlined body shape
Reduce surface roughness
What do shark denticles do?
Prevent flow separation (vortex generation), so reduce drag
How many land invasions did invertebrates do and what were they?
2
Molluscs (snails)
Arthropods (eurypterids- sea scorpions)
How many land invasions did vertebrates do and what were they?
1
Stout finned fish- subcarangiform swimmer, streamlined body, gills, gas bladder
Why transition to land?
New food sources
Avoid predators and competition
O2 abundance
Problems faced on the land
Temperature regulation
Water evaporation
Air breathing
Gamete desiccation
Gravity- water provides buoyancy to support body and food
Lift based propulsion not practical in air
What was the first arthropod onto land?
Eurypterids (sea scorpions)
Features of eurypterids
Large stout legs- capable of terrestrial locomotion
6 legged and 8 legged walking
What is the earliest terrestrial gastropod and when from?
Maturipupa
From the Carboniferous
What was Eusthenopteron?
Genus of sarcopterygian (lobe-finned fish)
From the Devonian
Limb-like fins that may have helped to pull it through shallow lagoons
What digits are suited to walking?
Forward facing
Gives traction to substrate
What was Ichthyostega?
Land dweller in the Devonian Half amphibian, half lobe-finned fish Strenghtened pectoral and pelvic girdles Robust zygapophyses Webbed toes Dragged belly along ground
What are zygapophyses?
Notches that allow vertebrae to lock together
Strenghtens, so better for land
What had the first 5 digit limb found?
Pederpes
Early Carniforous- ‘Romer’s gap’
Forward facing feet
5 digits
What were primitive gaits like?
Evolved from lateral undulations in fish swimming- still used by amphibians and reptiles eg. salamanders
Belly walkers
Forces on sprawling gait
Forces on the scapula, so has to be very robust
Forces on erect gait
Forces are also supported by the spine, so can have a smaller pelvis and scapula
3 types of posture + examples
Crouched- quail, rats
Sprawling- iguana
Upright- ostrich, deer
Ways of increasing locomotion speed
Get bigger
Increase stride frequency
Increase stride length
How to increase stride length
More upright posture Run on tips of toes Lengthen limbs Flex spine- eg. cheetah Increase distance travelled when feet are off the ground- eg. run instead of walk
Geometrically larger=
SA:V ratio decreases, so area to attach muscle decreases
Exoskeleton size limited
What are hydrostatic skeletons?
Mainly in aquatic invertebrates
Water is an imcompressible fluid, so can’t reduce its volume
Provides resistance for the contraction of muscles to act against
Some are reinforced with collagen to control and limit shape change
Locomotion in earth worms
Circular muscle contraction causes fluid to press on the longitudinal muscles
Long muscles stretch, elongating worm
Wave of contractions produces forward movement
Advantages of a hydrostatic skeleton
Some can take up O2 and water and excrete waste through the skin
Eliminates need for separate transport systems, saving energy
Skeletons are light compared to rigid skeletons, so less muscle mass is required to move them
Disadvantages of a hydrostatic skeleton
Little protection against desiccation
Restricted to aquatic environment unless very small
What are muscular hydrostats?
Constant volume of incompressible liquid
Instead of single fluid filled cavity, 3D matrix of muscle
Eg. elephant trunks, star nosed mole
Arthropod exoskeleton features
Chitinous
Covers entire body inc. eyes
Exoskeleton advantages
Protective layer
Helps prevent dessication
Exoskeleton disadvantages
Can’t expand as animal grows- moult- 2hrs, vulnerable
Size constraints
Stress similarity in terrestrial locomotion
Stress increases as get larger
Impossible to produce bones of size needed in a giant
But only if geometrically similar- support with thicker bones
What are plantigrade species?
Place the full length of the foot on the ground with each stride
Eg. humans, bears
What are digitigrade species?
Walk with most of the length of digits, but not soles of feet, in contact with ground
Eg. dogs, birds
What are unguligrade species?
Walk on their tiptoes, often hooves
Eg. horses, antelope
What does flexing the spine while moving do?
Lengthens the stride
What is walking?
One leg is always on the ground
Potential energy is dependent on height from the ground
Inverted pendulum motion
Potential energy to kinetic energy
What is running?
Aerial phase is present
Kinetic energy and potential energy are converted to elastic energy
Achilles tendon stores elastic energy, restores it
Advantages of bipedalism
Frees forelimbs for carrying/wings
Eyes set higher, so can see further
Reduces SA exposed to sun
Chimpanzee bipedalism
Small bums- unstable legs
Can’t extend knee-joints to straighten leg
Small Achilles tendon
What is flight?
‘Descending at more than 45 degrees from vertical (less than is falling)’
‘Controlled aerial behaviour with/without obvious aerodynamic structures’
4 flight subdivisions
Parachuting
Directed aerial descent
Gliding
Flapping flight
2 types of drag
Friction drag
Pressure drag
What is friction drag?
Depends on surface area in contact with the air
What is pressure drag?
Depends on the shape
Result of flow separation causing low pressure behind the object
What does parachuting require?
An air brake
Want to make as big a surface area as possible
What is controlled aerial descent?
Animals can use angular momentum
Or uneven air resistance (drag)
What is angular momentum?
Mass x speed x distance from pivot point
Change one and the other change to compensate
Allows uneven drag
What is uneven drag?
Can stick a limb out to change speed, direction etc
Can also generate some lift by spreading out limbs or laying flat
How do cats turn in the air?
Use angular momentum
Spread hind limbs wide, pull in fore-limbs
Turn front half quickly in one direction, hind legs move slowly in other direction
Then do the opposite- fore-limbs wide, hind narrow
Angular momentum of cats body is always 0
How do geckos always land on their feet?
Use their tail to right themselves in the air
Examples of vertebrate directed aerial descenders
Wallace’s flying frog
Flying gecko
What is lift?
Air has to travel further over the top of the wing
Produced in animals that glide
Drag is also produced, so animal still falls
Examples of animals that glide
Sugar gliders
Flying fish
Flying lizards
What does flapping (powered) flight require?
Thrust
Produced by reversing the circulation sense of the vortices shed from the animal
4 groups of animals that have evolved flapping flight separately
Insects
Pterosaurs
Bats
Birds
Insect adaptations for flight
Thin chitinous membrane wings
System of sclerotized veins
Pterosaur adaptations for flight
Elongated digit
Membrane wing
Bat adaptations for flight
Elongated digits
Membrane wing
Bird adaptations for flight
Feathered wing
Evolution of insect flight
Limited evidence
No transitional fossils found
Directed aerial control in ants
Only tree nesting species are capable of it
But morphologically similar to ground species- can only rotate in air
Gliding ants cannot glide at night
Tree ants that glide onto leaf litter often killed by other ants/insects
Evolution of pterosaur flight
220-65mya
No transitional fossil forms (half-winged)
Pterosaur skeleton features
Pteroid bone that supports the propatagium
Unique to pterosaurs
Don’t know orientation of bone
Wing membrane shapes in pterosaurs
Varied between different groups
Not many fossilised membranes
Membrane attachment sites vary
Some may have been bird-like, some more bat-like
How did pterosaurs move on land?
Track-ways suggest they were quadrupedal
Could maybe take off from land?
Evolution of bat flight
Arboreal origin- phylogeny and membrane attachment suggest this
But bats can take off from and move across the ground
Origin of bird flight theories
Wing-assisted incline running (WAIR)
What was wing-assisted incline running?
Jumping out of something high, or pouncing, ambushing prey from rocks
Stage of chick development may mirror flight development
Anatomical evidence of flight capabilities in Archaeopteryx
Small sternum
No keel
No foramen triosseum (hole in the shoulder for flight tendon)
Shoulder anatomy suggests dorsal elevation wasn’t possible
Anatomical evidence of flight capabilities in Confuciusornis
Small sternum
Shallow keel
No forament triosseum
Shoulder anatomy suggests dorsal elevation of the limb wasn’t possible
What are the pivotal flight structure in birds?
Flight feathers (thin feathers are not capable of sustaining flight)
Vane asymmetry in Archaeopteryx and Confuciusornis
Asymmetry of vanes similar to flightless modern birds
