Evolutionary origins
Related to elephants and other subungulates (hyraxes, aardvarks)• Hypothesized to have split off around
50-55 mya, similar to origin of Archaeocetes
Fossil record shows several genera• Now only two genera, four species
Steller’s Sea Cow (a dugong)
•Discovered in 1741
•Largest recent Sirenian
•Only cold water Sirenian
•Exploited by hunters
•Extinct in 1768
Body form/adaptations
•Fully aquatic
•Streamlined
•Minimal hair
•Lack hindlimbs, vestigial pelvic bones
•Propulsion and steering?
•Buoyancy control?
•Relatively shallow divers ~40 feet, 8
min.
•Water/ion balance Food: seagrass/seaweeds not useful
water source Kidneys Drinking water
•Thermoregulation Warm water species
•Manatee migrate to warm springs in winter
Low metabolic rates Large size helps keep warm Poor insulation (limited fat)
Manatee vibrassae and lipsPhoto: Mote Marine Lab
Dugong Photo: L. Murray
Feeding ecology• Eat seagrasses,
algae, other plants• Dugongs feed on
bottom only•Manatees more
flexible flexible lips, hand-like
forelimbs Can replace teeth
(dugongs don’t)• Inefficient eaters.
Why? Ruminant (foregut) vs.
sirenian (hindgut) symbionts
Daily consumption?
Part 2: Diving Physiology
• Diving times (select marine verts)
Leatherback turtle = 45 min Hawksbill turtle = 74 min Emperor penguin = 22 min Harbor seals = 30 min California sea lions = 30 min Northern elephant seal = 62 min Weddell seal (Antarctica) = 73 min Sperm Whale = 90+ min
Factors limiting dive time• The asphyxia triad:
Hypoxia: depletion of oxygen stores Hypercapnia: CO2 build-up pH change Switch to anaerobic metabolism
• Why a problem?
• Effects of prolonged asphyxia Weakening/death of tissues (why?) Differential effects on diff. tissues
• Temperature and asphyxia
• Lowered metabolic demands and asphyxia
Adaptations for dive timesMarine vs. terrestrial vertebrates• Increase oxygen supply
•Decrease oxygen demand
•Reduce deleterious effects
Increased oxygen supply
• Relatively large blood volume Huge blood vessels Role of inferior vena cava
•Weddell seal = 3X vol/kg of humans
Fig 3-1, Reynolds
Increased oxygen supply
• Increased red blood cell concentration
Potential problems viscosity clotting potential
Solutions• Ringed seal
• Weddell seal (*DISCUSSION!)
• Increased size of red blood cells Up to 20% larger
Increased oxygen supply• Oxygen stores in circulatory system
(per kg)Circluatory oxygen stores
0
10
20
30
40
50
60
70
Human
Leat
herb
ack t
urtle
Antar
ctic f
ur s
eal
Bottle
nose
dolph
in
King p
enguin
Wed
dell se
al
ml/k
g
Increased oxygen supply•Myoglobin has a
higher affinity than hemoglobin for O2
at any PP of O2 Consequences?
•Muscles: Use of Hb-bound vs. Mb-bound O2 Capillary densities in
marine mammal muscle?
Distribution of mitochondria?
Increased oxygen supply• Respiratory stores: Importance of
“lung capacity?” (*DISCUSSION!)
0
2
4
6
8
10
12
14
Human
Leat
herb
ack t
urtle
Antar
ctic f
ur s
eal
Bottle
nose
dolph
in
King p
enguin
Wed
dell se
al
ml/k
g
Increased oxygen supply• Summary: total oxygen stores (per kg)
0
10
20
30
40
50
60
70
80
90
100
Human
Leat
herb
ack t
urtle
Antar
ctic f
ur s
eal
Bottle
nose
dolph
in
King p
enguin
Wed
dell se
al
ml/k
g
Increased oxygen supply
• Adaptations to maximize O2 loading (surface) Heart rate? Respiratory rate? Revisit Hb vs. Mb
affinity for O2
•What happens to “waste” products (i.e. C O2 and lactate?)
Ringed seal: heart rate changes
Decreased oxygen demand
•What is the diving response? Respiration HR Blood flow
(ischemia)
•What initiates the diving response? Trigeminal nerve
Decreased oxygen demand
•Bradycardia Benefits? Effects on blood pressure? Extreme vs. moderate bradycardia
•Evidence for conscious control
Variability in HR during dive•*DISCUSSION: Weddell seals!
Decreased oxygen demand
• Ischemia Which tissues are
affected? Benefits
•Ischemia of viscera and skin
•Muscle (*DISCUSSION: how can reducing circulation to muscle actually increase aerobic dive limit?)
Tolerance: marine vs. terrestrial mammals
Decreased oxygen demand
•Lowering body temp. and/or BMR Benefits?
•Reduction of oxygen use•Decreased tissue damage
Evidence?•Sea lions and seals•Penguins
Adaptations to temp. decreases•Special fat•Countercurrent exchange -> heat where
needed