sio 133 - marine mammal sensory systems –...

SIO 133 - Marine Mammal Sensory Systems – Vision, Mechanoreception,

Chemoreception, Magnetoreception

Marine Mammal Sensory Systems

Visual

Auditory

Mechanoreception

Chemoreception

Magnetoreception

Light in the Ocean

Rapid attenuation of light with depth – 65% of visible light absorbed ~1m

Short wavelengths penetrate deeper – Blues and greens

Scattering due to particles and turbidity Refractive properties in water

Light in the Ocean

Morel 1974. Op6cal proper6es of pure water and pure sea water. In: Op#cal aspects of oceanography. Jerlov N. G., Steeman-‐Nielsen E. (eds.). 1-‐24.

Light in the Ocean

LeI: TransmiKance of daylight in the ocean in % per meter as a func6on of wavelength. I: extremely pure ocean water; II: turbid tropical-‐subtropical water; III: mid-‐la6tude water; 1-‐9: coastal waters of increasing turbidity. Incidence angle is 90° for the first three cases, 45° for the other cases. Right: Percentage of 465nm light reaching indicated depths for the same types of water. From Jerlov (1976).

Large eyes Increased photoreceptor density Increased % rods, decreased % cones Pigments for blue/green light Tapetum lucidum (eyeshine) Large dynamic pupillary range Rapid dark-adaptation rates

Adapt Vision to Underwater

How does the Human eye work?

Sclera

Refrac6ve Index Air = 1.000 Water = 1.333 Cornea = 1.376

Snell’s Law

Underwater Eye Cetacean

Dolphin

Operculum

Underwater Eye Pinniped

Odonotocetes: double slit pupil, double fovea

Pinnipeds: ver6cal pupil, single (normal) fovea

MARINE MAMMAL SCIENCE, 18(1):275-‐281 (January 2002)

Deep Divers have Blue Shifted Visual Pigment Sensitivity

Rhod

opsin

Dark adapta#on in pinnipeds, Levenson & Schusterman, 1999

Tapetum lucidum

Field of View

• Pinnipeds, otter, polar bears – Binocular vision – field i, depth percep#on h

• Cetaceans, sirenians – Monocular vision – fieldh, depth percep#on i

Visual Acuity

• Spherical lenses compensate for lack of refractive power in water – No bending of light at cornea in water

• Accommodative mechanisms in pinnipeds – Strong ciliary muscles to stretch lens – Flattened cornea – “Pinhole camera” effect in air

Adapta6on to Turbidity Reduced, poorly developed eyes Walrus, river dolphin, dugong

4) Denser innerva6on

Mystacial

Supraorbital

Whiskers or Vibrissae Different from terrestrial animals 1) Enlarged 2) S6ffer 3) Greater blood flow

Rhinal (phocids only)

• > 1000 nerves/follicle (humans 100/follicle)

• Sensi6ve to size, shape, surface structure of objects

• Detec6on of hydrodynamic mo6on

• Largest por6on of brain devoted to this sense

Seal Vibrissae

Harbor seals detect and track wakes up to 100m+ Sea lion shape recogni6on as fast and reliable as vision Walrus have 600+ highly mobile vibrissae, shapes to 0.4cm2

Sirenians • • • • •

Sensory hairs over body Facial sinus hairs Perioral “bristles” Highly movable “Prehensile” -‐ can evert and grasp!

Chemorecep6on: Olfac6on Generally not well developed, poorly studied • Cetaceans: non func6onal?

– Odontocetes: lack olfactory bulb and nerves – Mys#cetes: olfactory bulbs reduced or absent

• Manatees: poorly developed, rudimentary • Pinnipeds: good func6on in air?

– reduced olfactory structures – more reduced in phocids than otariids or odobenids

• OKers and polar bears: well developed

Harbor seals • Detect minute levels

of dimethyl sulfide • DMS emiKed by

blooms • Used to find fish?

Kowalewsky et al., 2005

Chemorecep6on: Gusta6on Generally not well developed anatomically, but poorly studied

• Dissolved substances detected by taste buds • All marine mammals have taste buds

– Dolphins: sour, sweet, biMer, salty – Sea lions: sour, biMer, salty (not sweet) – Usually worse than humans

• Psychophysical and physiological methods

Harbor seals • Detect >1%o

differences in salinity • Sensi6vity increased as

salinity increased • Seals have sal6er saliva

S#cken et al., 2000

Magnetorecep6on – Earth’s Magne6c Field

North Magnetic Pole: Dip angle = 90° (vertical) Total Field = ~60,000 nT

South Magnetic Pole: Dip angle = 90° (vertical) Total Field = ~60,000 nT

Magnetic Equator: Dip angle = 0° (horizontal) Total Field = ~30,000 nT

Magnetorecep6on – Magne6c Anomaly

US East Coast Local varia6on In magne6c field Due to crustal rocks

Cape Cod

Cape HaKeras

Correla6on of Stranding and Magne6c Lows

Distance from Stranding (km)

Kirschvink et al. JEB 120: 1-‐24 1986

• Whales and dolphins have magnetite in their heads, but it is not confirmed that they use it for magnetoreception.

Human Brain

Lateral view Cerebrum

Cerebellum

Dorsal view

Sensory informa6on is processed subcor6cally, and then in primary modality areas

Very similar to terrestrial mammals

Highly convoluted, extended auditory region

Small, few convolu6ons

brainmuseum.org

Cetacean BoKlenose Dolphin

Sirenian Florida Manatee

Pinniped Harbor Seal




Very similar to terrestrial mammals Highly convoluted,

extended auditory region


brainmuseum.org

Dolphin Brain –SagiKal View

Convolu6on Index = wrinkliness

Largest Brain on planet, 30 lbs!

Belongs to Sperm Whale

Absolute Brain Weight – Does it reflect intelligence?

Species Adult Brain Weight (grams)

Chimpanzee 450

Human 1,350

Bottlenosed dolphin

1,600

African elephant

6,075

Fin whale 7,200

Sperm Whale

9,200

Rela6ve Brain Weight Of all animals, man has the largest brain

in propor#on to his size” -‐ Aristotle Species Brain to Body Weight

Human 2.1 % Bottlenosed dolphin 1.2 % Chimpanzee 0.70 % African elephant 0.50 % Killer whale 0.10 % Cow 0.08 % Sperm Whale 0.02 %

Encephaliza6on Quo6ent (EQ) Human 7.4 Dolphin 5.6 Killer whale 2.9 Chimpanzee 2.5 Rhesus Monkey 2.1 Elephant 1.9 Whale 1.8 Dog 1.2 Cat 1.0 Horse 0.9 Sheep 0.8 Mouse 0.5 Rabbit 0.4

EQ = ra6o of brain weight of animal to brain weight of “typical” animal of same body weight EQ represents residual value of brain mass Es6mate of species’ intelligence based on brain/body size

Encephaliza#on quo#ent (EQ) • Odontocetes fall above mammalian regression line • Pinnipeds, sea oKers, polar bears fall on line • Manatees fall below

sio 133 - marine mammal sensory systems –...

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