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SIO 133 - Marine Mammal Sensory Systems – Vision, 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
MARINE MAMMAL SCIENCE, 18(1):275-‐281 (January 2002)
Deep Divers have Blue Shifted Visual Pigment Sensitivity
Rhod
opsin
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
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.
Very similar to terrestrial mammals
Highly convoluted, extended auditory region
Small, few convolu6ons
brainmuseum.org
Cetacean BoKlenose Dolphin
Sirenian Florida Manatee
Pinniped Harbor Seal
Cetacean BoKlenose Dolphin
Sirenian Florida Manatee
Pinniped Harbor Seal
Very similar to terrestrial mammals Highly convoluted,
extended auditory region
Small, few convolu6ons
brainmuseum.org
Very similar to terrestrial mammals Highly convoluted,
extended auditory region
Small, few convolu6ons
brainmuseum.org
Cetacean BoKlenose Dolphin
Sirenian Florida Manatee
Pinniped Harbor Seal
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