Sensory systems forelæsning (week 2)

Question 1

Intended learning outcomes

Answer 1

• Describe the overall anatomy and function of the cetacean and pinniped sensory system
• Discuss the various uses of the sensory system for foraging, navigation, and communication

Question 2

Sensory perception essential for survival in an aquatic environment

Answer 2

Physical conditions (abiotic and biotic)
Sensing predators and prey
Communication and foraging
Individual recognition
Navigation

Question 3

Perceived world differ for species and individuals

Answer 3

Body plan restrictions (cetacean vs. pinniped vs. Sirenia)
Small genetic differences
Disabilities (e.g. loss of eye)

Question 4

Sensory modalities include:

Answer 4

• Audition (acoustics)
• Vision
• Somatosensory perception (touch, pressure, temperature)
• Equilibrioception (balance)
• Chemoreception (taste and smell)
• Electroreception (electric fields)
• Magnetoreception (magnetic fields)

Marine mammals likely shift between sensory modalities for different uses and geographic distances

Question 5

Cetacean vision

Answer 5

Lateral location of eye give 120-130 degree panoramic vision

Function in air (short-sight) and underwater(normal)

High density of photoreceptors and tapetum lucidum (reflective layer) increases sensitivity

Glands protect from salt water

Question 6

Pinniped vision

Answer 6

Large eyes (except walrus) for diving/foraging

Function in air (short-sight) and underwater (normal)

Spherical: located on front of head

Increased sensitivity
- Thick tapetum = light sensitive
- well-developed in elephant seals

Harderian glands keep eyes wet

Question 7

Do marine mammals have colour vision?

Answer 7

• Rods sensitive to low light levels, but not colour
• Cones sensitive at high light levels, including colour vision

Marine mammals have many rods, but have lost S-cone (blue), and possess only one type M/L-cone (red/green)

Eye structure and molecular evidence suggest that marine mammals are colour blind.
…. However tests in captivity show that some pinnipeds and dolphins can distinguish colours

More research needed!!

Question 8

Somatosensory perception

Answer 8

Touch (pressure and strokes), pain and temperature
Receptors placed in dermis, muscles an joints
- Vibrissae (particular in pinnipeds and mysticetes)
- Skin furrows for tactile sensing and/or hydrodynamics
- Mechanoreceptors around blowhole of cetaceans
- Sensitive to touch in head region; social aspect?

Question 9

Vibrissae

Answer 9

Whiskers

• All pinnipeds
• 10-fold increase in nerve fibres
• Detect sensory stimuli such as sound, movement, acceleration
• Muscular control in walrus

Question 10

Humpback whale vibrissae

Answer 10

Vibrissae in humpback whale tubercles

Question 11

Bowhead whale vibrissae

Answer 11

Vibrissae in face and around blowhole
To sense prey, and the surface (ice)?

Bottlenose dolphins have similar system although without tiny hair.

Question 12

Equilibrioception

Answer 12

Sense of balance and movement in 3D environment
Vestibular system in the inner ear
- Two otoliths detect linear movement and gravity
- Semicircular canals detect rotation; canals smaller than in terrestrial mammals, perhaps to avoid overstimulation?

Question 13

Chemoreception

Answer 13

Olfaction (smell)
Gustation (taste)

A recent study suggest that marine mammals may locate prey by smelling/tasting dimethyl sulphide released when zooplankton grace on phytoplankton

Question 14

Olfaction

Answer 14

Smell
- Reduced compared to terrestrial mammals, in particular in cetaceans and sirenians
- Otarid olfaction better than phocid and walrus
- Mysticetes (in particular right whales) better than odontocetes

Question 15

Gustation

Answer 15

Taste
- taste buds in juvenile odontocetes, but not adults
- stellar sea lion and bottlenose dolphin can distinguish salty and bitter, and perhaps sweet
- dolphins and porpoises can distinguish levels of citric acid
- … however some genetic studies suggest that pathways are non-functioning?

Question 16

Electroreception

Answer 16

Detecting electric pulses/fields (ex: muscles of fish)
To date, only detected in Guiana dolphin

Are electroreceptors located within vibrissal crypt on rostrum? do they allow for detection of benthic prey?

Question 17

Magnetoreception

Answer 17

Perception of magnetic field
The earth’s magnetic field is regular, with few exceptions

Main mechanisms in animals:
- induction: magnetic field generates electric field that are detected by eletroreceptor cells (known in birds)
- ferromagnetic particles (ex; magnetite) align themselves in the magnetic field, like a compass (known in fish)

Dolphins can distinguish magnetic properties of objects
Some cetacean mass-stranding events hypothesised to correlate with local anomalies in geomagnetic fields.