Mammalia [Odontoceti, Mysticeti, Pinnipedia]

• Odontoceti


  Toothed whale
• Mysticeti


  Baleen whlaes
• Pinnipeda


  Seals
• Definition of marine mammal


  Mammal that depends on marine ecosystems for their existence

  • Forage underwater
  • Mate and/or give birth underwater
  • Sleep underwater
  • On land?
  • Occupy/rely on aquatic (if not strictly marine) habitats
  • Have evolved similar anatomical features, including large body size, streamlined shape, insulation in the form of blubber and dense fur, and in most cases, a modified appendicular skeleton resulting in reduction in the size of appendages
  • Posses some similar physiological adaptations for diving, thermoregulation, osmoregulation, communication and orientation
• Class: Mammalia ~6,000 species


  Mammals

  • Vertebrate
  • Mammary glands - milk young
  • Hair at some point in life
  • Middle ear bones
  • Quadruped (vestigial hindlimb in e.g. cetaceans)
  • Neocortex (layer in brain)
  • (Mostly) endothermic - warm blooded
• Pressure


  As pressure rises, volume decreases: not a problem for the body, just for air spaces

  For every 10m, pressure rises by 1 atmosphere [At 100m depth, the volume is 1/10 of the surface volume, and pressure is 10 times greater

  
• Pressure

  Mechanical distortion or compression of tissues, especially gas filled spaces

  Higher gas tension in the lungs resulting in increased gas absorption into tissues

  Gas tension may be higher than ambient pressure during ascent, which means gas bubbles

  Simply, at depth the diver is a long way from its most precious source, oxygen
• Coping with pressure


  [Compliance: relationship between pressure and volume]

  • Loss of facial sinuses
  • Lung collapse
  • Flexible ribcage
  • Flexible trachea

  
• Depth

  • Shallow divers
  • Intermediate divers [150-200m maximum, 5-10 mins]
  • Deep divers

  
• Breathing

  • Breathing reflex - voluntary breathers
  • Maximise oxygen exchange - 80-90% of air exchanged
  • Whale blow: powerful gas evacuation
• Oxygen supply


  Mechanisms for storing and consuming O2 efficiently:

  • Decreased heart rate (bradycardia)
  • Increased O2 storage
  • Redistribution of blood flow
  • Efficient locomotor patterns
  • Withstand low O2 levels

  Oxygen storage:

  
• Oxygen storage

  
• Managing oxygen stores: Bradycardia


  Rapidly reduced heart rate

  • Decrease up to 1/10 of normal
  • Seals: 120 beats/min to 6 beats/min

  
• Managing oxygen stores: Blood flow


  Reduced cardiac output: widespread peripheral vasoconstriction of arterial vessels to maintain blood pressure

  • Constriction of blood flow to muscles/extremities
  • Blood flow mainly to brain, heart and vital organs

  
• Insulation


  Thermal conductivity and insulation are the inverse of each other (high insulation, low conductivity)

  Type of insulation is a function of haul-out climate, time spent in water, depth of dives

  
• Blubber [primary function is insulation]


  Blubber is the product of evolutionary and adaptation pressures that go beyond thermal insulation capacity

  • Source of fuel and energy during fasting
  • Metabolism of the lipid stored produces metabolically derived water
  • Buoyant
  • Provides shape
  • Shield for injury caused by fighting
  • Misconception that blubber is simply fat cells
  • Blubber is a highly specialised organ comprising a loose collagen protein matrix interspersed with lipid depots
  • Heated blubber still holds it shape
• Blubber

  
• Fur

  
• Fur in polar bears

  • No pigments
  • Hollow

  
• Fur vs blubber

  
• Food webs


  A food web in an ecosystem is a complex and interconnected network of feeding relationships among various organisms

  
• Diet composition


  [Specific prey species vary depending on marine mammal's species and geographic location]

  
• Non-vocal communication

  • Harbour seals can slap their fore flippers against their body when disturbed
  • Bottlenose dolphins and bubble emissions
  • Breaching
• Sound emissions by Odontocetes


  Classified into two broad categories of frequency-varying continuous tonal sounds:

  • Whistles, categorized as social sounds, appear to be used for intraspecific communications
  • Clicks (used for echolocation or communication)

  Some odontocete species never/rarely whistle(e.g., harbor porpoise, hector's dolphin, sperm whale)
• A spectrogram of whistles emitted by a white-beaked dolphin

  
• Signature whistles


  Signature whistles were observed in three behavioural contexts:

  • Mother/calf reunions - mothers produced their own signature whistle, afterwhich the calves re-joined her
  • Alloparental care - older male and female spotted dolphins in an association with younger dolphins produced their own signature whistles prior to the retrieval of younger dolphins
  • Courtship - female and male spotted dolphins were observed repetitively broadcasting their own signature whistle during attempted courtship and mating activity

  Variety of sound emissions, across behavioural context, species and age

  
• What is an echolocation and when is it used?

  Echolocation is the process in which an organism projects acoustic signals and obtains a sense of its surrounding from the echoes it receives

  Toothed whales (including dolphins) use the ability to echolocate for navigating, locating and catching prey, and to avoid predators

  
• Dialect


  Dialect is best reserved for sound emission differences on a local scale among neighbouring populations, which can potentially intermix.

  The functional significance of dialects is controversial, with some maintaining that dialects are related to:

  • song learning and social adaptation
  • mating and are of evolutionary significance

  Orcas display highly social behaviour and live in pods. These pods produce several discrete calls and call repertoires differ significantly among pods
• Source of odontocete vocalization


  Recent experimental data have conclusively shown that the phonic lips, a constriction in the soft tissue nasal passage between the blowhole and skull, are the sources of odontocete vocalization

  
• Sound emissions by Mysticeti


  The vocalizations of baleen whales can be divided into two general categories:

  • Songs (up to 30 min long)
  • Calls

  The calls can be further subdivided into three categories:

  1. Simple calls
  2. Complex calls
  3. Clicks [pulses, knocks, grunts]
• Humpback whales' complex songs

  • Songs from the north Pacific, south Pacific, and Atlantic populations are different
  • Singing peaks during the winter months when humpback whales migrate to warmer waters at lower latitudes
  • Some singing also occurs during the summer and fall
  • Songs from consecutive years are very similar, but songs across non-consecutive years will have fewer similarities
  • Singers are most likely only males
  • Singing whales are often alone and tend to remain stationary
• Sound emissions by Pinnipeds


  The number of vocalizations produced by pinnipeds is correlated with their mating system and whether mating occurs underwater or on land

  Except for male walruses, pinnipeds do not whistle
• Evolution of unique traits - Morphology

  
• Evolution of unique traits - Morphology

  
• Hydrodynamics


  Sea water is 800 times more dense than air

  • Supports weight/size
  • Viscous and hard to move through (drag)

  Two aspects of locomotion

  1. Hydrodynamic adaptations (increase efficiency)
  2. Modes of propulsion (flukes, flippers, paddling)

  Adaptations depend on amount of time spent in water and level of activity
• Modes of propulsion

  • Stroke efficiency and modification of the appendage(s)
  • Hydrodynamic lift-based momentum exchange to generate thrust
  • Very different mechanisms across different groups

  
• Otariids: Fore-Flippers

  
• Phocids: Rear-Flippers

  
• Cetaceans: Flukes and Flippers

  
• Cetaceans: Flukes and Flippers