MARINA MAMMALS-ADAPTATIONS

ADAPTATIONS

Adaptations to the Marine Environment

Challenges of living in water

– Drag (physical forces that reduce forward movement)

– 60x more viscous than air and 800x denser

– But provides support – easy to generate propulsion

– Pressure change

– Additional 1 atm/10m; crushing at depth

– Heat loss

– 24x thermal conductivity of air

– Salt Balance

– High salinity challenges water and electrolyte balance

– No usable oxygen

– Must take oxygen from the surface

ADAPTATIONS

Adaptations involve

• Swimming and locomotion

• Thermoregulation

• Osmoregulation

• Diving and breath holding

Structure and Locomotion

Major trends in marine mammals skeletal system

• Streamlining of the body

– Loss or reduction of much of the appendicular skeleton

• Enlarged propulsive appendages

Cetaceans typify trends

• Gradual reduction of limbs and streamlining

ADAPTATIONS

• Ambulocetus

– could walk on land

– in water, like sea otters

• There are costs associated with transitional forms!

Body shape and hydrodynamics

• Drag can be calculated by

• p = fluid density, V = swimming velocity, A = frontal area of body, Cd = drag coefficient (accounts for

flow characteristics of fluid around body)

Consequences of drag

• Swimming faster causes more drag fast

• Larger frontal area increases drag

• Poor flow increases drag

ADAPTATIONS

Four types of drag

• 1. Frictional Drag

– Interaction of the animal’s surface with the water surrounding its body

– Cab be reduced by reducing SA/VOL ratio

• 2. Pressure Drag

– Need to displace the amount of water equal to animals largest frontal area

• Size and shape affect magnitude

• Predominate when submerged

• 3. Induced Drag

– Associated with flow around flippers, fins, etc

– Results from pressure difference between two surfaces of hydrofoil and formation of vortices at tips

ADAPTATIONS

• 4. Wave Drag

– Energy that could be used for forward motion used to create waves

– Total drag 4-5x higher when moving near surface

– Becomes negligible 3 body diameter below surface

How to minimize drag

• Be streamlined

– Ideal shape is bluntly rounded at front, round cross section, and tapered toward rear

– Finess ratio (FR) helps to find optimum length/area

– Optimum FR for fast-swimming 3-7 (optimum 4.5)

– Odontocetes, otariids, phocids 3.3-8.0

– Balaenopteridae 4.8-8.1, Balaenidae 3.3-8.0

– Weird ones: northern right whale dolphin (Lissodelphis borealis), minks, river otters 9-11

ADAPTATIONS

How to minimize drag

– Appendages with rounded leading edges that taper toward tail

– Similar morphology in very different lineages

– Don’t try to swim fast on the surface or minimize time at the surface

– If you must come to the surface fast, reduce drag by porpoising or leaping while getting air

– Cross-over speed: speed at which leaping becomes cheaper energetically

– C-O speed 5 m/sec in spotted dolphins increases with body size until too costly at >10m

Locomotion Modes in Marine Mammals

• Several modes of locomotion found in marine mammals that reflect degree of aquatic specialization

ADAPTATIONS

• We’ll look at structure and mode of locomotion for major taxa before returning to the implications for

energetic costs

Polar bear

• Largest bear species, but smaller than recent ancestors

• Large feet aid in swimming

• Pulls through water with forelimbs, hindlimbs trail behind

• Postscapular fossa allows attachment of subscapularis muscle

– Position aids in pulling heavy body for swimming (climbing in other bears)

• Large paws distrubute body weight on land

ADAPTATIONS

• Foot pads have small soft papillae that increase friction with ice

• Usually walk with lateral, not diagonal, legs

• Can reach 40 kph on land

Sea otter

• Increased development of posterior areas

– Greater muscle mass

– Increased height of neural spines and transverse processes that provide attachment

• Pelvis is elevated to almost in line with spine

• Femur, tibia, fibula relatively short

• Elongated toe bones

– Skin web between hinddigits

– Hind foot 2x as wide when digits spread

ADAPTATIONS

– 4th and 5th digits closely bound to add rigidity for propulsion

• Terrestrial locomotion slow and clumsy because of large hind feet

– Walk or bounce on land, can’t run (bounce to go fast)

– Use alternate limbs

Sea otter aquatic locomotion

• Pelvic paddling using hind limb propulsion and pelvic undulation of the vertebral column

• Giant extinct otter was forelimb paddler

• Three swimming modes

– Ventral up swimming

– Ventral down swimming

– Alternate ventral up and down swimming

– Ventral up swimming

ADAPTATIONS

• Used during food consumption and initial escape

• Alternate or simultaneous strokes of hind feet

• Some lateral undulation of tail to maneuver

– Ventral down swimming

• During intermediate speed traveling and before high speed diving

• Alternate or simultaneous strokes of hind feet, no role of tail or forefoot

– Alternate ventral up and down swimming

• Use hindpaws

• During periods of grooming while traveling forward

Pinnipeds

– Front and hind limbs lie within body outline

ADAPTATIONS

– Phocids have eversion of the ilium for greater muscle attachment responsible for body movements in

swimming

– Hind flippers have elongated digits I and V

Otariids: Terrestrial locomotion

– Limb based, can use foreflippers to push up, but propulsion more from movements of head and neck

rather than hind limbs

– Walk and gallop gaits, depend on environment

– Sandy: limbs moved in alternative and independent sequence

– Rocky: bounding that displaces center of gravity vertically. Hind limbs in unison.

ADAPTATIONS

Phocids: Terrestrial locomotion

• Move through vertical undulations of the body trunk

– Arch lumbar region and bring pelvis forward while sternum take weight

– Extend anterior end of body while pelvis takes weight

– Forelimbs may help by lifting and thrusting anterior regions

– Can’t turn hind limbs forward; not used

• Some ice-dwelling species use lateral undulations of the body

– Use backward strokes of forelimbs and lateral movement of posterior torso (hind limbs lifted)

– Can be very fast

– Seen in leopard, crabeater, ribbon, harp seals

Odobenids: Terrestrial locomotion

ADAPTATIONS

• Similar to otariids, can rotate hind limbs forward

• Weight is supported by belly on ground rather than limbs!

• Feet move in lateral sequence followed by lunge for propulsion

Otariids: Aquatic locomotion

• Pectoral oscillation (forelimb flapping)

– Produce thrust like birds in flight

– Move in unison, act as oscillatory hydrofoils

– Power, paddle, and recover phases

• Hind limbs provide maneuverability

Phocids: Aquatic locomotion

• Pelvic oscillation (hind limb swimming)

ADAPTATIONS

– Hind limbs used in lateral undulation of lumbosacral region

• Forelimbs steer

Odobenids: Aquatic locomotion

• Pelvic oscillation like phocids

Cetaceans: structure to aid locomotion

• Thoracic and lumbar vertebrae restrained by strong collagenous subdermal conntective tissue sheath mammals

–

ADAPTATIONS

– Gives rigidity to thorax

– Provides enlarged surface for tail flexor and extensor muscles

• Ligaments between vertebrae in tension during extension and flexion of the tail

– Dolphin vertebral column can store elastic energy and dampen oscillations and control body

deformation during swimming

Cetacean locomotion

• Vertical oscillations of the tail

• Caudal propulsion improves efficiency at higher sustained velocities

• Thrust is generated by up- and downstrokes, but more from upstroke

ADAPTATIONS

• Elastic rebound of connective tissues increases energy efficiency

Maneuverability: an odontocete problem

• Maresh et al. 2004 investigated the problem of how Tursiops truncatus is able to catch smaller, more

maneuverable prey

• What did they discover?

• How did they address this problem?

Sirenian Locomotion

• Caudal oscillation for propulsion

– Body changes pitch (degree changes with power of stroke)

– Tail can be used to bank, steer and roll

• Slow swimmers, unable to sustain or reach high speeds (usually 0.6-0.8 m/s)

ADAPTATIONS

– Slow speeds allows greater maneuverability

– Can reach 22 kpm (6 m/s) during flight sprints

• Flippers primarily for maneuvering, but may use to slowly paddle (juveniles may use a lot)

– manatee shoulder muscles reflect habitats that require greater maneuvering than dugongs

– Manatees use mainly for left-right turns

– Dugongs also use to maintain balance

Evolution of Sirenian Locomotion

• Three stages

– Quadropedal: trusts with alternate limbs

– Dorsovenral spinal undulation and thrusts of hindlimbs

– Tail swimming only

ADAPTATIONS

Cost of Transport (COT)

– Swimming and diving are major energy sinks

– Can account for 82% of daytime activity budget (Tursiops)

– COT useful for comparing locomotor efficiencies

– Where P Is Power required to move body mass (M) at a given velocity (V)

– Power curve is usually U shaped – lowest transport cost at intermediate velocities

– COT varies with body size

– Swimming is least costly (body supported)

– Cetaceans reduce COT by wave-riding

• COT of dolphins lower than pinnipeds

• COT is higher than predicted for fishes of their size (due to high metabolic rate, warm blooded)

ADAPTATIONS

• Swimming and migration speeds (2m/s) very close to predicted optimum for minimizing COT

Swimming speeds

• Cruising swimming speeds not very different based on swimming modes and body sizes

– Amazingly narrow range 1.3-3.6 m/s

• Sprint speeds can be much higher

Adaptations: Thermoregulation and Osmoregulation

Two major challenges in water

• Staying warm

– Waters are cooler than internal body temperatures of mammals; many marine mammals live in polar

climates

ADAPTATIONS

– Water is a good heat conductor

– Transfers heat 24x faster than air

– Body heat is lost rapidly

– Typical mammalian hair isn’t the greatest insulator when wet

– Many solutions to staying warm

• Maintaining salt balance

– Steep gradient between solute concentrations in blood and that in saltwater

– Trick is maintaining electrolyte balance in body fluids: keep the water from flowing out of the body

Staying warm: methods

• Change body shape (be round)

– Low SA/VOL ratio reduces rate of heat loss

ADAPTATIONS

• Have external insulation (be furry)

– Fur can help to insulate the body and trap body heat

• Have internal insulation (be fat)

– Fat and blubber stores are great insulators and can be burned to produce heat

• Generate your own heat (be a furnace)

– Increase activity

– Shiver

– Process food

– Metabolize fat (non shivering heat production)

• Don’t waste heat (be a heat conserver)

– Countercurrent heat exchangers

– Peripheral vasoconstriction

• Choose the right place to warm (cool)

ADAPTATIONS

– Behavioral thermoregulation

Which of these are long-term and which are short term?

– Change body shape (be round)

– Have external insulation (be furry)

– Have internal insulation (be fat)

– Generate your own heat (be a furnace)

– Don’t waste heat (be a heat conserver)

– Choose the right place to warm (cool)

Being round

ADAPTATIONS

• SA/VOL ratios must be optimized with streamlining

• Marine mammals have, on average 23% lower SA than similar sized terrestrial mammals

• Many species in cold climates are very stocky

External insulation: Fur

• Polar bears, sea otters, and pinnipeds covered by fur, but fur differs among species

• Consists of two layers

– Guard hairs (outer protective layer)

– Underfur hairs (soft inner layer)

• Polar bear hair once thought to direct light to skin to warm animal is incorrect

ADAPTATIONS

Sea otter fur

• Most dense fur of any mammal

– 125,000 hairs/cm2 (twice fur seal)

– Greatly reduces heat loss

• Guard hairs sparse

– Protect underhair integrity when wet

– Trap air when emerge from water

• Underhairs are wavy

– Trap and maintain air when submerged

• Lack arrector pili muscles that erect hair

– May help in streamlining by letting hair lay flat during submersion

ADAPTATIONS

• Only source of insulation yet almost never leave water

– Cost: 12% of day spent grooming to maintain water repellency and insulative value

Pinniped pelage

• Monk and elephant seals and walrus lack underfur

• Otarrid fur is uniformly arranged, phocid and walrus fur clumped

• Lack arrector pili muscles that erect hair

• Ntal coat differs from adult coat

– Monk and elephant seal pups are black

– Phocines, walrus white or gray

ADAPTATIONS

– Otarrids dark brown to black

– Lanugo is longer than adult pelage and helps conserve heat on land, but is not a good insulator in the

water

– White hair focuses heat and long hairs trap heat near body

Moulting

• Phocids, sea otters, and beluga whale molt annually

• Otariids renew pelt gradually throughout year and many cetaceans lose skin continuously

ADAPTATIONS

• Phocids must molt on shore to keep skin warm enough

– For pinnipeds, opportunity to renew and repair pelt and epidermis

– Occurs in summer and autumn in S. hemisphere

– More variable timing in N. hemisphere usually in spring

– Begins around face then abdomen and back

– Speed variable (25d elephant seal; 10-170d harbor seal

– Usually involves hairs lost individually, but monk and elephant seals shed attached to sheets of epidermis

ADAPTATIONS

Natal Moulting

– Usually lost in few days to few months

– Hooded and harbor seals lose in utero

– Likely because natal coat evolved for ice breeding, loss is secondary adaptation to land breeding

– Unlikely since hooded seal on ice

– More likely adaptation for being inundated by water at early age (natal coat poor when wet)

ADAPTATIONS

Coloration of Coverings

• Coloration of marine mammals can serve a variety of functions

– Camouflage

– Communication

– Species ID

– Sexual display

– Foraging aid

Phocid coloration

• Only pinnipeds that aren’t fairly uniform

• Pagophilic (ice breeding) species have disruptive coloration of contrasting light and dark

ADAPTATIONS

– Harp and ribbon seal patterns develop with age and vary by gender (most extreme in males)

• Many color patters help seals blend in

Cetacean coloration

• Three types

– Uniform (e.g. beluga)

– Spotted or striped with sharp colored areas on head side, belly, flukes (e.g. killer whale)

– Saddled or countershaded (e.g. most dolphins)

• Helps to blend in when seen from above or below

• Presence of “capes” can provide information about rotation to other group members

ADAPTATIONS

Internal insulation: blubber, the choice insulation

• Many marine mammals make use of blubber (hypodermis) to stay warm

– Loose connective tissue composed of fat cells interlayered with collagen bundles

– Loosely connected to underlying muscle

– Thickness and lipid content vary with species, age, sex, location, and season

• Bottlenose dolphins may vary up to 2mm/month

Blubber

• Otariids rely on fur and underlying blubber

ADAPTATIONS

• Phocids, sirenians, and cetaceans rely solely on a think blubber layer

• Blubber thinnest in sirenians and sea otters, thickest in blue whales (ave 23 cm, max 50 cm depth)

Blubber thermal conductivity

– Thermal conductivity is inverse of insulative value

– Depends on thickness and peripheral blood flow

– Thermal conductivity largely influenced by lipid content

• Higher lipid content and greater thickness at higher latitudes

ADAPTATIONS

• Harbor porpoise blubber (81% lipid) has 4x insulative value of spotted dolphin (55% lipid)

– Pinniped blubber better insulator than cetacean blubber because little fibrous material

– Insulation value depends on distribution

– if distributed around body core, lose heat more slowly

Pinniped distribution+blubber thickness

• High latitude distribution of some pinnipeds may be limited by insulation layer

– Cold air temperatures may be limiting during breeding season through effects on pups that are fasting after weaning

ADAPTATIONS

– Thinner blubber layer and lower metabolic rate to conserve blubber for entering water

– Appears to be case for gray seals, but generality unclear

Other uses of blubber

• Used in metabolic heat production as well as insulation

• Distributed to optimize streamlining

• Serves as energy store

– Most of energy stores for some species

• Possible anti-predator function in cetaceans

– Appears to be thicker than needed in some locations

ADAPTATIONS

Heat conservation: Heat exchangers

• Rete mirabilia (miraculous network)

– Massive contorted spiral of blood vessels (primarily arteries with some thin-walled veins)

– Form blocks of tissue on inner dorsal wall of thoracic cavity and extremities or periphery of the

body

– Found in many other taxa

• Sharks, tuna, billfish, wading birds, anteaters, lemurs, sloths

ADAPTATIONS

Countercurrent heat exchangers

• Retia work as Countercurrent heat exchangers

– Works through transfer of heat by setting up heat differential between opposing blood flow

– Cools down warm blood as it flows to periphery

– Warms cool blood moving back to body

– Found in flippers, fins, flukes

– Conserve body temperature

– Baleen whales have CCHE in mouths to reduce loss of heat when feeding in cold water

– Sirenian CCHE best developed in tail, but found throughout body

ADAPTATIONS

Countercurrent heat exchangers and staying cool

• CCHE associated with reproductive tracts

• Phocids and dolphins use to cool testes or fetus

– Phocids run from extreme hindflippers (6-7°C lower temp @ testes than body core)

– Dolphins run from flukes and dorsal fin

Countercurrent heat exchangers and staying cool (Elsner et al. 2004)

– Bowhead whales have CCE and arteriovenous anatosomes (AVAs)

– To stay warm, blood is shunted into CCE and away from AVAs

ADAPTATIONS

– To cool, blood is shunted to AVAs

Peripheral vasoconstriction

• Helps in diving, but also reduces amount of heat lost

– Less blood cooled

Heat production

• Variety of mechanisms

– High metabolic rate

– Appear to be relatively high for many MM

– Sirenians are an exception: 25-30% of expected for terrestrial mammal

– Increase activity

ADAPTATIONS

– May be necessary for many species to stay warm (e.g. Tursiops truncatus, Stenella longirostris)

– Process food

– Shivering

– Non-shivering thermogenesis (fat burning)

Sea otter heat production

• Have high basal metabolic rate (2.4x expected for terrestrial mammal)

• Increase activity level as water temperature drops

• Use heat produced during digestion to increase core body temperature

ADAPTATIONS

• Relative use of these in other marine mammals poorly known

Behavioral thermoregulation

• Environment differs in temperature, and marine mammals can make use of this to warm up or stay cool

– Warm surface waters for deep divers

– Basking for pinnipeds

– Will also rest in water with flippers sticking up into air

– Seasonal migrations

– Manatees and power plants

Thermoregulation in pinniped pups

ADAPTATIONS

• Lack blubber at birth

• Possess brown fat (also found in hibernating mammals and human babies)

– Keeps pups warm through nonshivering thermogenesis: metabolizing fat to produce heat

– Converted into blubber in a few days

Thermoregulation on land

– Adaptations to heat conservation when in the water may lead to difficulties staying cool on land for pinnipeds

ADAPTATIONS

– Some have hypothesized that pinniped distribution toward low latitudes is limited by high

temperatures on land and difficulties in staying cool

– In warmer areas, pinnipeds need to move into the water to cool off occasionally

– Elephant seals flip sand on their backs to stay cool by digging up cool sand

– Monk seals dig holes to cool layers or rest on damp sand

– Northern fur seals pant

ADAPTATIONS

Osmoregulation

• Refers to maintaining salt (electrolytes) and water balance in internal environment

• Marine mammals are hypoosmotic

– Body fluids have lower salt concentration than surrounding water

– In danger of losing water through osmosis

Balancing salt and water

• Feeding and water ingestion alter osmoregulatory balance

– Most (or all) water ingestion from food intake

• Reestablished by urine, feces, evaporation; Kidneys are organ responsible for balance

ADAPTATIONS

Kidneys of marine mammals

– Many species have large kidneys, but not all (e.g. elephant seals)

– Kidney:body mass ratios

• 0.44-1.0% cetaceans; 0.3-0.4% terrestrial mammals

– Pinnipeds, cetaceans, polar bear and sea otter have reniculate kidney

– Many small lobes (reniculi)

– Each lobe functions as mini-kidney

– Cetaceans have 100s to 3000 reniculi in kidney

– Number of reniculi depends on salinity of diet

• Sirenian kidneys are not reniculate

ADAPTATIONS

• Dugong kidneys are elongate, smooth, and have some characteristics of ungulate kidneys

• Dugongs are physiologically independent of freshwater

• Manatees must have access to fresh or brackish water to maintain osmotic balance for prolonged periods

Drinking and water sources

• Marine mammals will drink freshwater when it is available

– Some pinnipeds in polar areas eat ice

– Is it needed? Not really

ADAPTATIONS

• Water sources

– Drinking

– Water in food

• Fish/invertebrates 60-80% water

– Water from own stores (catabolism)

• 1.07 g water/g fat; 0.4 g water/ g protein

• Used extensively during fasting

Drinking saltwater

• Allows high rate of urea production to get rid of more wastes

• Associated with high protein diet

– Need to get rid of more nitrogen

ADAPTATIONS

• Sea otters drink lots of seawater

• Cetaceans and pinnipeds will drink seawater (especially adult male otariids that have prolonged fasting)

Reducing water loss

• Few salt glands present in pinnipeds and none in cetaceans

• Reduced urine output

• Countercurrent moisture exchangers in respiratory tract

Maintaining water balance

• Water loss from exhalation can be extreme (especially on land)

ADAPTATIONS

– Some pinnipeds (elephant and gray seals) conserve water during breathing

– Countercurrent blood flow in the nose sets up temperature gradients

– Increased surface area in nasal passages

– Moisture in exhalation condenses on epithelium then humidifies inhaled air on way to the lungs

Adaptations: Sensory Systems

Marine mammal sensory abilities

• Life underwater presents unique challenges in trying to navigate, find food, avoid predators, and interact

ADAPTATIONS

with conspecifics due to low light and visibility conditions

• Most species rely heavily on numerous sensory systems working in concert

• Many marine mammal systems highly modified from terrestrial mammals

• In this lecture, we’ll look at all but sound production and echolocation

Mechanoreception

• Includes:

– Touch

– Hydrodynamic reception

– Sensing vibration and water disturbance

ADAPTATIONS

– Audition

– Sensing sound waves

Touch

• Other than whiskers, receptor units are distributed across entire body

• Head area most sensitive for tactile information

– Skin sensitivity in dolphins may be used to help with drag reduction, but most interest in other

species focuses on whiskers

• Most specialized mechanoreceptors are vibrissae (whiskers or sinus hairs)

ADAPTATIONS

– Specialized sensory hairs

– Diameter and structure reflect does not reflect importance but adaptation to signals received and

transmitted (sensitivity and function)

– Used for tactile information but may also detect vibrations

Pinniped Vibrissae

• Occur only on face

• Differ from terrestrial mammals

– Enlargement of whiskers and site of innervation different in pinnipeds

ADAPTATIONS

– Stiffer hair in pinnipeds

– Follicles surrounded by 3 (not 2) blood sinuses

• Three types of vibrissae

– Rhinal

• 1 or 2/side just posterior to nostril (phocids only)

– Supraorbital

• Above eye, mostly immobile

– Mystacial

• Upper lip, mobile

• Most prominent and numerous

• Walruses have most (600-700)

ADAPTATIONS

Pinniped vibrissae structure

– Number of nerve fibers (1000-1600) passing through capsule in Phoca hispida is 10x greater than

terrestrial species with sensitive whiskers

– Mechanoreception is decreased when skin is cold, so how do pinnipeds manage to use vibrissae in such

cold conditions?

– No vasoconstriction to vibrissal pads (selective heating)

– Highlights importance of this sensory mode

Pinniped Vibrissae

ADAPTATIONS

• Extremely sensitive

– Baltic seal vibrissae have 10x nerve fibers of terrestrial mammals

– Size discrimination abilities of harbor seals and CA sea lions are similar to primate hands and close

to visual capabilities of the seal which shows the importance of this sensory system (Denhardt and

Kaminski 1995)

– Move head side to side when object is small but don’t need to for large objects (touch multiple vibrissae simultaneously)

ADAPTATIONS

Pinniped Vibrissae function

• Tactile receptors

– Mystacial vibrissae used for discrimination of textured surfaces (location, shape, size, surface

texture)

• Navigation

– Can help navigation in total darkness and low visibility conditions

– Use as speedometer, sense direction changes

• Prey detection and capture

– Even blind seals found to be well-fed in wild

– Often used to scan for benthic prey

ADAPTATIONS

Cetacean Vibrissae

– Only on head along margins of upper and lower jaws

– Structure and innervation suggest sensory role

– Mysticetes have ~100 very thin (0.3 mm dia) immobile vibrissae on upper and lower jaw

– Most odontocetes lose hair postnatally; 2-10 follicles on either side of upper jaw

– Exception are river dolphins which possess many well developed immobile vibrissae on both jaws,

but not yet shown if they are true vibrissae

ADAPTATIONS

Sirenian Vibrissae

– Entire muzzle covered with flexible bristle-like hairs

– Used for discrimination of textured surfaces

– Also have perioral bristles on the upper lip, oral cavity and lower jaw that are very rigid and moveable

– Manipulation of objects, further exploration once grasped

– Manatees can control facial vibrissae which may have role in feeding

– Sinus hairs also lightly scattered over body

ADAPTATIONS

The Sirenian mouth

• Combination of muscular lips and different types of facial vibrissae form a unique system

• Manatees can use this “haptic” system in a prehensile fashion to investigate objects and manipulate food

into mouth

Sea otter and polar bear vibrissae

• Sea otters have all three types of vibrissae

– Mystacial whiskers most numerous

• Few vibrissae in polar bears

ADAPTATIONS

Hydrodynamic Reception

– Can vibrissae of pinnipeds detect pelagic fish through water disturbances? (Denhardt et al. 1998)

– Vibrissae respond to vibrations, but took an experiment to show that this worked for water

disturbances

– Vibrissae are tuned to frequency range of fish-generated water movements

– Fish leave trails of disturbance that last minutes

– Harbor seals can detect and tract trails up to 40m long (based on blind-folded seal following

minisub)

ADAPTATIONS

– Sensory abilities of vibrissae help explain success of pinnipeds in dark and murky water

Audition (hearing)

• Some changes in marine mammals

– Closing mechanisms to protect the ear from penetrating water under pressure at depth

– Loss or reduction of external ear flaps to increase streamlining

– No real tradeoff for underwater hearing since external ear tissue is acoustically transparent

underwater

• A major problem is how to transmit sounds to the inner ear and localize sources

ADAPTATIONS

Sound localization

• In horizontal plane, determined by interaural time and intensity differences

• Sound travels 4.5x faster in water so information processing must be better

– Tursiops has best discrimination ability for both types of information of any mammal tested

– can localize sounds other than echolocation separated by 2-3°

• Tursiops is equally good at sound localization in vertical plane, but we don’t know how!

ADAPTATIONS

How do marine mammals localize sounds?

• Terrestrial mammals underwater can’t localize sounds

– Bone conducts sound to both ears almost simultaneously

• Auditory organs of odontocetes are largely isolated from the skull to avoid bone conduction (less so in

other MM)

– How does sound reach the inner ear in odontocetes?

Sound reception in odontocetes

ADAPTATIONS

• Two pathways

– Ear canal functions to detect low frequency sounds

– Mandible (lower jaw) can detect high frequency sounds

– Fat channels in lower jaw have impedance close to water and channel sound over pan bone to

petrotympanic bullae

Sound reception in other MM

• Mysticetes still unknown, but conventional pathway of terrestrial mammals is functional

– Distance between ears makes localization less problematic with bone conduction

ADAPTATIONS

• Manatees have lipid-filled zygomatic process which appears to transmit sound to squamosal-periotic

complex (mechanism similar to odontocetes)

Sound reception in pinnipeds

• Appear to use conventional pathway

• Bone conduction probably most important for sound transmission

– Should limit directional sensitivity with sound through skull

– good sound-localization in some sp (Phoca vitulina)

ADAPTATIONS

– Poor and variable in others (Zalophus califonianus)

• Ear functional in air sensitivity depends on species

– California sea lion: best in air

– Common seal: equal

– Northern elephant seal: better underwater

Hearing ranges and discrimination

• Odontocetes have widest hearing range

– Tursiops best hearing 12-75 kHz but up to 150 kHz detected

– Can discriminate frequency difference of 0.2-0.8% from 2 kHz-130 kHz

ADAPTATIONS

• Frequency discrimination is less precise and operates over a lower frequency range in pinnipeds and

sirenians

Weeding out background noise

• Marine mammals superior to terrestrial mammals in detecting signals in noise

• However, this is often not enough and vocalizations may be used to reduce masking effects

Vision

• Electromagnetic radiation changes intensity and composition as it moves deeper in water

ADAPTATIONS

– Becomes more monochromatic and spectrum shifts to shorter wavelengths as depth increases due to

scattering and absorption

• Eyes of marine mammals adapted to see in water and in air

Habitat and vision

• Spectral sensitivity of visual pigments should correspond to the habitat where vision is most important

– Deep-sea fishes have blue-sensitive pigments

– Shallow water fishes are green-sensitive

• Generally fits for marine mammals

ADAPTATIONS

– Shallow diving species green or blue-green

• E.g. spotted seal, manatee, gray whale

– Deep-diving species tend to have blue

• E.g. elephant seal, Baird’s beaked whale

– Reflects habitats as well (e.g. open ocean is bluer; arctic is greener, Weddell Seal)

Marine Mammal Eyes

• Generally resemble nocturnal mammals

– Dilatable pupil maximizes light collection

– Choroid located between retina and outer coating of eye with tapetum lucidum (light reflecting

layer)

ADAPTATIONS

– Retina dominated by rod-like receptors but cone-like receptors (or second type or receptor) strongly

suggested or verified

• Two types of cones in mammals

– S: short wavelength sensitive

– M/L: medium to long wavelength sensitive

• Absence of S cones associated with nocturnal habits

• Cetaceans and pinnipeds lack S cones, which appears to be adaptation for redder coastal waters

ADAPTATIONS

– Loss may have occurred early in evolution or should see S-cones in pelagic species (we don’t)

Do marine mammals see in color?

• Mixed results from psychophysical methods

– Demonstrated in spotted seals, California sea lions, manatees

– Failed in bottlenose dolphins

– Fur seals can discriminate blue and green but not red and yellow from grey shades

• Color discrimination and adaptive nature of vision is still unclear

ADAPTATIONS

Adaptations to seeing in water

– Cornea and encased fluids have about the same refractive index as saltwater; optically inefficient

– Refractive power restricted to lens when submerged

– Most pinnipeds and cetaceans have a large almost spherical lens with high refractive power allowing

normal vision underwater

– Trade-off: when cornea regains power in air, results in extreme near-sightedness

ADAPTATIONS

River dolphin eyes

• Most river habitats extremely murky

• Sensing light and dark for orienting to surface is all that is important

• Platanista indi and P. gangetica have lost the lens of the eye and are essentially blind

Visual Acuity

• Perception of fine detail at various distances

• Visual acuity degrades faster in air than in water

• Acuity underwater is poorer than in-air acuity of many primates, but better than many terrestrial

ADAPTATIONS

mammals with good vision

– e.g. elephants, antelope

Chemoreception: Olfaction

• Relatively little attention in marine mammals

• Relative to terrestrial mammals, marine mammal olfactory systems

– Somewhat reduced in pinnipeds and sirenians

– Very reduced in baleen whales

– Absent in odontocetes

Olfaction in pinnipeds

• Olfactory systems well-developed

• Have vomeronasal organ

ADAPTATIONS

– Can detect scents of food in mouth

• Olfaction may function in mother-pup recognition

• More research needed to understand role of olfaction in pinnipeds

Chemoreception: Gustation

• Taste buds in oral cavity provide information about dissolved substances

• Taste appears to be limited in pinnipeds and small odontocetes

– Fewer taste buds that terrestrial mammals

ADAPTATIONS

– They can discriminate some chemicals in sea water and can detect the four primary tastes (sour,

bitter, salty, sweet) but for most of them, detection thresholds are much higher (especially salty)

• More taste buds present in sirenians

ADAPTATIONS

Taste in pinnipeds and other marine mammals

• Use of taste in marine mammals poorly known

• May be highly specialized for detecting salinity differences at high (marine) salinities

– Harbor seals shown to be very good at this

– Could be used for finding vertical layers

– For navigation to/along oceanic fronts?