Sensory Systems

• Chemoreception– Olfaction– Gustation

• Vision

• Touch

• Hearing

Function of Sensory Systems

Navigate

Find food

Avoid predators

Locate calves

Mate underwater

Function of Sensory Systems

• Environments change

• Other animals (friends, enemies, predators) change behaviour

• Each animal needs information on those factors to make appropriate decisions

• The senses allow animals to receive this information

Olfaction

• Mysticetes: – Olfactory bulb only in fetus– Olfactory tract: in adult stage

• Odontocetes:– Bulb and tract only in fetus

• Pinnipeds: all structures present– Function– Maybe mother-pup recognition?

}Evolution:

changes in skull

morphology

Gustation• In comparison to terrestrial mammals:

– Taste buds modified– Fewer buds on tongue

What does a Dolphin/Seal taste compared to

humans?Threshold for

Sour

Bitter

Salty

Sweet

Bottlenose dolphin

7x higher

2x higher

10x higher

10x higher

Cal. Sea Lion

Similar

1000x higher

20x higher

No reaction

Possible Functions of Gustation

• Communication

• Orientation– Spatial salinity gradients

• Humans can discriminate solutions with at least 18% salinity difference

• Seals can discriminate solutions with as little as 4% difference (lowest of all mammals)

Sense of Touch

-well developed in cetaceans

-skin is sensitive

-important to pinnipeds

Whales have hair at birth.

Some whales keep snout hair as adult

(Mysticetes and few odontocetes)

Tactile: Pinniped Vibrissae

• Mystacial vibrissae on muzzle

• Supraorbital vibrissae above each eye

• Rhinal vibrissae in Phocids, at back of muzzle

Touch: Sensory Hairs

• Sensory hairs:– Sirenians: Muzzle hair– Odontocetes: Usually

hairless after infancy– But: river dolphins have

jaws covered with thin bristles

– Baleen whales: ~ 100 vibrissae around jaws

Sense of Vision-visibility may be limited in water

-light is extinguished

-eyes may not be important for long

range orientation

-close range are important

Vision:The Marine Mammal Eye

• Similar to our eye

• Cornea not important (as opposed to humans)

• Spherical lens (Ganges river dolphins does not have lens)

• Ciliary muscles:• none in cetaceans

• pinnipeds

Vision: Detection and Acuity

• Detection – Becoming aware of an object– Determined by sensitivity of photo cells

• Acuity– after detection, a clear image of the object is

needed: is it a conspecific, or a predator?– How much detail can one see?– Depends on the focusing ability of optical

system in eye

Visual Ability in Air and Water

• Pinnipeds and dolphins have good visual acuity in water and air– seals can detect moving objects during moonlit

night at 466m depth

• Reflective layer behind retina (Tapetum lucidum)

Sensory Systems: the Pinnipeds

The head of a pinniped is equipped with sense organs to receive stimuli from its environment. (Antarctic fur seal)

Order Carnivora the Pinnipeds

Family Otariidae Family Phocidae

Family Odobenidae

Seal DivingSeal Diving

CasidheCasidhe Dyke, Marine Mammals 4912 Dyke, Marine Mammals 4912

Vision

Southern Elephant Seal

Walrus

Thigmotactic: Sense of Touch

Elephant Seal Pups

Hooker Sea Lion With Pup

Sense of Smell

-important to detect predator

-olfactory device reduced in phocids,

larger in otariids

-mating

-social interaction

Sense of Smell

Sense of Taste

THE END

THANK YOU

Visibility and Colour under Water

0

10

20

30

40

50

60

70

80

Feet

Long wavelength Short wavelength