Marine Vertebrates: Lecture 11

Part 1: Marine Mammals, Order Sirenia

Part 2: Diving, Part 1

Part 1: Order SireniaManatees and Dugongs

ManateePhoto: R. Rattner

DugongPhotographer unknown

The mermaid-sirenian connection

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)

Feeding ecology

•Seagrass, algae, other plants

Order SireniaManatees and Dugongs

ManateePhoto: R. Rattner

DugongPhotographer unknown

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?

Sirenia: Distribution

Boating and manatees don’t mix!

Manatee with prop scarsPhoto: L. Osleen

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

Are most dives aerobic or anaerobic?

•Primarily aerobic (will discuss…)

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

• Increased concentration of hemoglobin/RBC

Increased oxygen supply• Oxygen stores in circulatory system

(per kg)Circluatory oxygen stores

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Increased oxygen supply• Increased myoglobin stores (per kg)

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!)

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Increased oxygen supply• Summary: total oxygen stores (per kg)

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dell se

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ml/k

g

Metabolic rate (per kg) vs. size

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

Decreased oxygen demand

•Efficient swimming: Weddell seals