Sensory Systems

Question 0

Peripheral sensory nerves

Answer 0

1. capture an environmental signal
2. filter it
3. transduce it into a neural signal
4. send processed info to CNS

Question 1

Sensory systems

Answer 1

allow animals to receive and process info about their surroundings • medium and message
• highly selective filters
• lots of variation – species-specific models
• humans – more optic vs. auditory nerves
• marine mammals – unique b/c air-adapted senses aren

Question 2

Multi-modal approach

Answer 2

– integration of multiple sensory systems
I. Mechanoreception (touch, hydrodynamic reception, audition) II. Magnetic Detection
III. Vision
IV. Chemoreception (olfaction and gustation)

Question 3

TOUCH

Answer 3

• with exception of whiskers (i.e. vibrissae) - entire body
surface, with focus on head
• cetaceans – active damping along body surface b/c of turbulence experienced during high speed swimming
Tests of tactile sensitivity:
! highest - head, i.e. 2.5 cm around blowhole (anterior higher than posterior – related to surfacing?), 5 cm around each eye, rostrum, melon
! lowest – back (in front and behind dorsal)

Question 4

Sensory Hairs

Answer 4

= vibrissae – primary touch-reception organ (vs. pelage hairs)
• occurrence and distribution varies
• e.g. baleen whales, odontocetes, river
dolphins

Question 5

Vibrissal Follicles

Answer 5

• reception of vibrational information
• intricate structures and densely innervated (e.g. ringed seals – 1000 – 16,000 nerve fibers per follicle!)
• perception of tactile information achieved through physical contact with object
• discrimination of macrospatial qualities (e.g. size and shape)
• haptic sense – cutaneous mechanosensation and kinaesthetics

Question 6

Sirenian Vibrissae

Answer 6

• have vibrissae all over bodies (structural differences) and don

Question 7

Pinniped Vibrissae

Answer 7

1. mystacial vibrissae
2. supraorbital vibrissae
3. rhinal vibrissae (only phocids)
   Studies of walruses, California sea lions, and harbor seals ! size, shape, surface structure using mystacial vibrissae
   e.g. walrus – shape discrimination down to 0.4 cm2, California sea lion – shape discrimination of objects < 0.33 cm in diameter
   Vibrissal capablities and temperature:
   • studies of harbour seals • unaltered capacity in cold
   • vibrissal pads stay warm ! separate vibrissal blood circulation/vessel properties
   • energetic price vs. need for tactile info

Question 8

B. HYDRODYNAMIC RECEPTION (in pinnipeds)

Answer 8

• lack of evidence for existence of sonar in pinnipeds
• acquire food in low light/visibility conditions
! Can vibrissae provide sensory info for detection of prey?

Question 9

Hydrodynamic sensory system:

Answer 9

• lateral line in fish • harbor seal study
• vibrissae serve as hydrodynamic receptor system
• spectral sensitivity highly tuned to frequency range of fish-generated water movements (trails persist)
• seals detected trails up to 40 m!

Question 10

AUDITION

Answer 10

Hearing – ability to hear sound by detecting pressure/vibrations in the ear
which are then transduced into nerve impulses that are perceived by the brain
sound waves enter ear canal (outer ear) ! ear drum vibrates! transferred to ossicles (middle ear)! cause fluid in cochlea to move (inner ear) ! sensory hairs move (organ of Corti)! create neural signals!
to auditory nerve (VIII)!
to brain
• hearing ranges are size and niche related
• mammalian ears scale to size, i.e. highest frequency an animal can hear is inversely proportional to body mass
• smaller animals – good ultrasonic hearing

Question 11

Outer Ear

Answer 11

in land mammals and some marine mammals, involves pinnae; localization and channeling of sound; ear drum

Question 12

Middle Ear

Answer 12

energy transformer and impedance matching device!mechanical vibration into fluid vibration
• increased stiffness in these components improves efficiency of transmission of high frequencies
• adding mass favors low frequencies
• dolphins – have ossicular chains stiffened with bony struts and fused articulations; stiff membranes

Question 13

Inner Ear

Answer 13

cochlea and basilar membrane
• similar to above – stiffness of membrane = high frequency specialization; more mass and less stiff = low frequency
• also relates to body size, i.e. scales with size
• bottlenose dolphin should have hearing upper
hearing limit of 16 kHz!actually 160 kHz!
• marine mammal inner ears – precocial and probably function in utero

Question 14

Marine Mammal Hearing

Answer 14

• tested – behavioral or electrophysiological • auditory evoked potential (AEP)/auditory
brainstem response (ABR)
• hearing curves are U-shaped; data on 12 spp.
• evolution occurred in response to characteristics of water!extent of ear modifications reflects level of aquatic exposure
• structural adaptations to pressure
• peak sensitivities – consistent with vocalization data
• marine mammals hear best at ultrasonic frequencies due to unique adaptations to aquatic environment

Question 15

ODONTOCETES
• Sound localization:

Answer 15

• underwater – air conductivity replaced by bone conductivity
• odontocetes – ears have no substantial bony association with skull
• suspended by ligaments in foam filled cavity outside the skull
• effectively acoustically isolated from bone conduction ! particularly important in echolocation
• dolphins have 2 sound receiving systems: 1. ear canals (lower frequency sounds) and 2. mandibular fat channels in jaw (higher frequency sounds – echolocation)
• audiograms – very wide range and strong discrimination Sound localization:
• occurs in air via interaural difference/delay (~ .00003 seconds); smaller head, smaller IATD
• because of high speed of sound travel underwater ! reaches both ears virtually simultaneously in humans
• information processing based on time or sound level works more precisely in fully aquatic mammals; related to sites of sound reception (but not understood…)

Question 16

2. MYSTICETES

Answer 16

• pathway of sound recognition – largely unknown
• suggest conventional pathway still functional (large distance
between ears)
• experiments prove they can localize sounds underwater

Question 17

3. SIRENIANS

Answer 17

• modified pathway to inner ear like odontocetes (via fluid filled zygomatic process )
• hearing not well developed ! particularly with sound localization
• problem: inability to detect approach of boats

Question 18

4. PINNIPEDS:

Answer 18

• no apparent novel pathway of sound transmission
• no separation of auditory structures from skull
• yet have good sound-localization skills underwater (?)
• 2 theories – dual systems or adaptations for one environment
• phocids vs. otariids
• less developed than odontocetes but good discrimination capacities

Question 19

II. MAGNETIC DETECTION

Answer 19

• water has almost no effect on magnetic flux ! should be effective
• biomagnetism – 2 types of magnetite = 1. formed by biochemical processes in body, and 2. ferromagnetic pollutants
• search for magnetite in body – very challenging! ! dura mater (which increases with age – confounding!)
• behavioral and migratory evidence that they use magnetic info to navigate!ocean sea floor has N-S alternating bands of magnetic orientation (with some E-W info)
• strandings info: in UK (dead vs. live strandings – correlated to lows/valleys in magnetic fields that intersect coasts or islands); in US – similar; in New Zealand – no correlation
• laboratory experiments – largely unsuccessful • some field correlations

Question 20

VISION Light in the marine environment

Answer 20

• light changes in quality and intensity • absorption and scattering
• more monochromatic and shift towards shorter wavelengths
• alterations in photon flux density with depth • countershading
• adaptations for visual acuity in 2 media

Question 21

Eye Structure

Answer 21

• most have large eyes
• highly dilatable pupil
• tapetum lucidum
• retinas dominated by rods
• high density of photoreceptors

Question 22

Rods and the spectral sensitivity hypothesis:

Answer 22

• the photosensitive pigments in photoreceptors (in rods) are adapted to particular photic environment
• basic correlation exists in marine mammals (primarily cetaceans)
• diving whales/open ocean: peak sensitivity = 485 nm
• cetaceans in green coastal waters: peak = 500-550 nm

Question 23

Color vision

Answer 23

• pinnipeds - limited evidence of presence of both cones and rods; identified in harbour seals and harp seals
• proven cone presence in Tursiops ! doesn

Question 24

Visual acuity (in and out of water)

Answer 24

• how well an animal can resolve features
• tested, e.g. with lights and/or black and white stripes
• in general, have improved acuity underwater
• have large spherical lens to compensate for loss of corneal refraction
• but then need to compensate for cornea-air refraction above water
• large spherical lenses and very small pupils
• California sea lions - area of flattened surface on
cornea
• bottlenose dolphins – crescent-shaped pupils ! allows for selective use of peripheral light above water
• Platanista gangetica - have no lens in eyes
• manatees – more rods than cones; no tapetum lucidum • sea otters – can change shape of lens

Question 25

Olfaction

Answer 25

• in general - decline in parallel with aquatic adaptation
• pinnipeds - reduced but possess well-developed olfactory systems; behavioral

Question 26

Gustation

Answer 26

• deliver info about dissolved substances via taste buds
• number of taste buds reduced in pinnipeds and odontocetes
• BUT – do possess ability to distinguish tastes/chemicals
• study of California sea lion and bottlenose dolphins ! sour , bitter, salty, sweet (careful in interpretation….)
• use of spatial salinity variations – spatial orientation and food (harbour seals - detected changes at 4% +)