Marine Vertebrates: Lecture 11 Part 1: Marine Mammals, Order Sirenia Part 2: Diving, Part 1

Part 1: Order Sirenia Manatees and Dugongs Manatee Photo: R. Rattner Dugong Photographer unknown

The mermaid-sirenian connection

Evolutionary origins  Related to elephants and other subungulates (hyraxes, aardvarks) Hypothesized to have split off around 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 Sirenia Manatees and Dugongs Manatee Photo: R. Rattner Dugong Photographer unknown

Manatee vibrassae and lips Photo: 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 scars Photo: 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 times Marine 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)

Increased oxygen supply Increased myoglobin stores (per kg)

Increased oxygen supply Myoglobin has a higher affinity than hemoglobin for O 2 at any PP of O 2  Consequences? Muscles: Use of Hb- bound vs. Mb-bound O 2  Capillary densities in marine mammal muscle?  Distribution of mitochondria?

Increased oxygen supply Respiratory stores: Importance of “lung capacity?” (*DISCUSSION!)

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

Metabolic rate (per kg) vs. size

Increased oxygen supply Adaptations to maximize O 2 loading (surface)  Heart rate?  Respiratory rate?  Revisit Hb vs. Mb affinity for O 2 What happens to “waste” products (i.e. C O 2 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