Marine Mammal Adaptations Integument The outer covering such as the skin or fur of an animal o The mammalian integument is a complex multi layered structure Epidermis Outermost layer cells are often keratinized and provide water proofing Epidermal structures include hair nails claws sebaceous oil and sweat glands Dermis Middle layer formed by two regions of connective tissue Papillary dermis has finger like projections each one carries blood vessels and verves toa position near the overlying epidermal cells Reticular dermis forms a connection with the underlying hypodermis Hypodermis Bottom layer a more loosely woven connective tissue layer Thermoregulation o Mammals are homeothermic endotherms with a high 36 to 38 C and stable body temperature o Water conducts heat away from the body 25 times faster than air Adaptations to deal with this Low Surface area to Volume ratio decreases the relative area across which heat is lost o Marine mammals tend to be large which means they have a small surface area to volume ratio thus reducing heat loss Reducing thermal conductance i e insulation o Fur Good in air but loses most of its insulation when wet Only the sea otter and fur seals have dense enough fur that the skin remains dry under water Sea otters also have a hydrophobic lipid squalene that helps keep fur waterproof o Fat Marine mammals use blubber a thick subcutaneous layer of fat for extra insulation Blubber can be up to 30 of total body weight Not nearly as effective as dry fur but better in the water Insulation depends on thickness and lipid content o Many marine mammals use both for insulation o Marine mammals may also face the problem of excess body heat especially in tropical regions when they are swimming a lot Bypass insulation by transferring heat to areas of little insulation Pinnipeds the underside of the flippers Cetaceans the fluke dorsal fin and flippers Counter current heat exchanger See Figure Two sets of pipes moving fluid between warm and cold areas can transfer heat very effectively These are the arteries and veins that run to and from the flippers fluke and fin Drag Reduction o Because of the increased viscosity of water over air life in the marine environment means more drag o The energy used in order to move a body through a medium is directly proportional to its drag o Therefore reducing drag means that marine mammals save energy or swim faster Adaptations to reduce drag Reduce hair or the guard hairs are the leading hairs they are flattened and thus for a smooth surface when wetted Streamlining reduces pressure drag o The hydrofoil shape is best at reducing pressure drag Buoyancy Control o When a body is submerged in water it displaces a volume of water equivalent to its own volume If the weight of the body is less than or equal to the weight of the water it displaces it experiences a net upward force and floats If the weight of the body is greater than the weight of the water it displaces it sinks o Mammals are made of some stuff bone and muscle that are denser than water o Other stuff like air filled lungs body fluids fats oils and blubber are less dense than water o Two mechanisms to avoid sinking Reduce the amount of muscle and bone Increase the amount of air body fluid fat oil and blubber Locomotion o Muscles pull on bones which are attached at joints thus creating leverage in order to pull water behind the animal and thus thrust it forward o A lever system can be designed to optimize either its force output or the velocity at which it moves Fource output is increased by increasing The force in The mechanical advantage of the lever system Example California Sea Lion Force in is increased by the large muscles attached to the upper arm bone Mechanical advantage is created by shortening the humerus o Propulsive efficiency is also increased by the shape of the paddle Flukes in cetaceans Hind flippers in phocids Front flippers in Otariids o The hydrofoil shape of these structures creates thrust as well as lift and thus facilitates locomotion Skull Morphologies o In pinnipeds otters and sirenians the skull morphology is very similar to that of a terrestrial mammal o Cetacean skulls are different Both odontocetes and mysticetes have a cranial elongation of the bones that form the rostrum the snout and a shortening of the braincase Mysticetes also have a tremendously elongated maxilla from which the long sheets of baleen hang The nostrils have migrated farther back on the head which helps to breathe while in the water o Sound production Pinnipeds Produce normal barks and growls like a dog but also produce high frequency sounds which may be used for echolocation These other sounds are probably not produced in the larynx but somewhere else Odontocetes Produce high pitched sounds used for echolocation Sounds are produced in the nasal plug and elaborate nasal sac system Nasal air sacs steeply sloping maxillary bones and the rostrum reflect sounds and help focus sound through the melon which focuses the sound Respiratory System o Many marine mammals are deep divers Pressure increases with depth such that every 10m is an additional atomosphere of pressure At high pressures nitrogen becomes solvent in body tissues When it comes out of solution it can rupture the tissue causing the bends How do marine mammals avoid this Oxygen is stored in the blood and muscles and air is kept out of areas that are in contact with blood o For this reason many seals actually exhale before they dive Marine mammal lungs are reinforced so that they don t collapse under the pressure and thus trap air where nitrogen could be absorbed into the blood o Breathing in the water How to keep from choking Used to think the watery blow of large whales was evidence that they inhaled seawater into their lungs Not true How do deep diving animals keep water from entering their nostrils How do they feed without breathing Nostrils close tightly o Pinnipeds the neutral position is to have the nostrils closed with a nasal plug sitting tightly against the bone o Odontocetes the larynx forms an elongated goosebeaklike structure that fits rigidly into the elongated nasal passage Food passes around the larynx when swallowing and no food or fluids enter the respiratory system The intranarial within nose position of the larynx effectively separates the respiratory tract from the digestive tract to a greater extent than that found in any other mammal o Also allows odontocetes to simultaneously echolocate and