Morphology and Locomotion Flashcards
What are some ways that marine mammals are adapted to locomotion in water?
- Flippers
- Streamlined body shapes
- No limbs
What are some challenges associated with locomotion in water?
- Water is more dense than air
- Water is more viscous than air
- The forces of drag are greater in water than air
Define drag
The rate of removal of momentum from a moving body immersed in fluid
Describe the relationship between energy and drag
The energy required to swim is proportional to drag and velocity
More drag = more energy spent
What are the three types of drag that can be experienced in water?
- Viscous drag (skin friction)
- Pressure drag
- Wave drag
Boundary Layer
Thin layer of fluid whose velocity is affected by the body’s surface
Viscous Drag
Occurs due to friction of fluid within the boundary layer
Only occurs next to the body’s surface
Describe the relationship between surface area and speed in regards to viscous drag
The higher the surface area and the higher the speed, the more vicious drag will be produced
Smaller animals = higher viscous drag
What are some adaptations that can reduce viscous drag?
- Smooth surfaces
- Position and morphology of guard hairs (ex: pinnipeds, and sea otters)
Guard hairs will flatten when wet to form a smooth surface
How does having a high turnover rate of epidermal cells decrease viscous drag in cetaceans?
- Cetaceans shed their skin up to every 2 hrs
- This allows them to maintain smooth clean skin thus reducing viscous drag
Define integument
A tough outer protective layer of an animal or plant
(ex: skin)
What are some functions of integument?
- Thermoregulation
- Reduction of drag
- Buoyancy control (ex: blubber)
How can blubber help control the buoyancy of marine mammals?
- Mammalian bodies = more dense than sea water
- Blubber = less dense than water
- Blubber is important in maintaining positive buoyancy
Describe how blubber in Right whales affected the development of ship alarms
- Right whales have thick blubber which allows them to surface rapidly and sit right underneath the water (close to the surface) making them hard to see by ships
- Ship collisions with Right whales lead to the development of ship alarms
- It was though that the whales would hear the alarm and move out of the way
- This did not work and was never implemented
Pressure Drag
Occurs due to the distribution of pressure around a body
When a fluid doesn’t adhere to an objects surface the resulting difference in pressure will oppose the objects motion
How does a streamlined body shape help reduce pressure drag?
Streamlined bodies create a lower pressure wake (flow is less separated) resulting in less drag
How can blubber influence body streamlining
Blubber disposition can sculpt a streamlined body shape
Describe the relationship between surface area and speed in regards to pressure drag
The higher the surface area and the higher the speed, the more pressure drag will be produced
Smaller animals = higher pressure drag
What is the fitness ratio (FR) for streamlining?
Chord length (length of body) / Maximum thickness
Long and skinny organisms have a high FR, short and fat organisms have a low FR
Why are the fitness ratios of marine mammals important?
Indicates how much work (energy) an organism must spend in order to swim efficiently
Fully aquatic mammals exhibit the most streamlining
How do the forces of drag affect rorquals?
Lunge feeding is energetically costly due to the expansion of the buccal cavity (equivalent to opening a parachute under water) which increases drag
How does lunge feeding affect rorquals diving capabilities?
Due to the high energetic costs of lunge feeding (increased drag) rorquals do not have an increased diving capacity in spite of their large size
Describe how blubber can act as a biological spring?
- Blubber in tail stock provides rigidity / stores tension allowing the organism to capture, store, and release kinetic energy
- On the upstroke, kinetic energy is stored (think spring being compressed)
- On the downstroke kinetic energy is released
Wave Drag
- Experienced in near surface water
- Kinetic energy is transformed into potential energy in the form waves
- Energy is used in producing waves rather than moving forward
How can marine mammals easily reduce wave drag?
Swim deeper
Wave drag = negligible at deep depths
Reynolds Number
Dimensionless number that describes the importance of drag in fluid flow
R = Body length X Swimming velocity / Water viscosity / Water density
What is Reynolds Number primarily influenced by?
Size and velocity (varies within / between species)
Viscosity and density of water do not change much
What form of drag is important for animals that have low Reynolds Numbers?
Skin friction
What form of drag is important for animals that have high Reynolds Numbers?
Pressure Drag
Marine mammals have high Reynolds Numbers (the forces of pressure drag are important in terms of efficiency of movement)
What are some ways that drag can be morphologically reduced?
- Low surface area (large body size)
- Smooth body surface
- Smooth integument (loss of modification of hair)
- Streamlining
What behavioral adaptations are used to reduce drag?
- Leaping or porpoising at the surface (drag is lower in air than in water)
- Calf drafting
- Wave / bow riding
- Gliding while diving
What is the mode of locomotion in Pinnipeds?
Appendicular musculoskeletal system (back and forth)
What is the mode of locomotion in Otariids?
Forelimb propulsion
What is the mode of locomotion in Phocids and Odobenids?
Lateral hindlimb propulsion
What are the modes of locomotion in cetaceans and sirenians?
- Axial musculoskeletal system
- Alternating contraction of epaxial (upstroke) and hypaxial (downstroke) muscles
- Thrust from flukes (on both up and down stroke)
Generates lift
Describe the connective tissue depth in cetaceans
- Compact bodies due to connective tissue
- Resist torsion and maintains body shape
- Anchors muscles and tendons
