Breath holding marine vertebrates Flashcards
Saltwater crocodiles use breath holding for …
- predator avoidance (particularly for juveniles)
- foraging / hunting
- social interaction (mating)
How long can large individuals hold their breath for (crocs)
- Large individuals (>1000 kg) may be able to breath-hold for 2h (at resting metabolic rate at 25 ˚C
- Active-swimming dives are much shorter
how do crocodiles show dive response
- brachycardia + peripheral vasoconstriction → lower oxygen demand
Crocodile cardio + resp system
- Crocodiles use lungs as O2 store, CO2 sink, and to regulate buoyancy
- the most complex hearts of all vertebrates:
- may redistribute flow to brain & heart in dives (Axelsson et al., 1996) -> BUT whether this actually occurs is uncertain (Eme et al., 2007)
Marine iguana (Amblyrhynchus cristatus; Galapagos iguana) feeding
- Feeds primarily on marine algae
- Smaller juveniles forage in intertidal;
larger adults dive subtidally
Marine iguana swimming
- Swims by body undulation- costs are higher to propel small animal through surf and surge
Large individuals foraging (iguana)
Large individuals forage offshore for >45 mins
but many short dives
* Max dive depth ~30 m and most dives are much shallower
Green sea turtle (Chelonia mydas) diving
- deep active dives typically 10-20 m, 20-30 mins (in migration)
- mostly shorter shallower dives (e.g. feeding on seagrass)
- can submerge for hours at rest (e.g. for sleep)
- Leatherback turtle (Dermochelys coriacea):
deepest dives >1200 m, >60 mins (during migration)
most dives (>99%) shallower (<300 m; Houghton et al., 2008)
Deep leatherback dives - feeding
- in transit occur around midday
- Foraging for deep patches of gelatinous zooplankton
- If found during deep dive, turtle may remain to feed at night
- No deep dives observed at feeding grounds
Problems of deep-diving at ambient pressure
4 physiological challenges from absorbing gas under pressure:
(i) oxygen toxicity
(ii) safe decompression of saturated tissues
(iii) inert gas narcosis
(iv) high-pressure nervous syndrome
Oxygen toxicity
Hyperbaric O2 → problems with brain/CNS (seizures, blackout)
* At 90 metres deep in ambient-pressure diving, normal 21% O2
in air → equivalent to 200% O2 at surface pressure
* Problem solved: use lower % O2 for deep phase of dives
(e.g. 1% O2 for very deep dives, e.g. deepest saturation dives)
decompression of saturated tissues
- Absorbing gas under pressure → more of them in solution
- Reducing pressure during ascent → gas comes out of solution
- Causes decompression sickness, aka “the bends” (joint pain from bubbles in body fluids → contortions) & can damage lungs in particular (pulmonary embolism)
Inert gas narcosis
Main inert gas (78% N2) has narcotic effect at high pressure
* Dissolves in cell membranes, disrupting normal signalling
Helium gas narcosis
- Helium has less of a narcotic effect under pressure N2
- helium still has narcotic effects
at greater depths
High pressure nervous syndrome
HPNS results from pressure effects on central nervous system
* Symptoms include tremors, eye twitch, headaches, fatigue
- inert gas narcosis is “opposite”
(overexcitation of nervous responses, rather than narcosis)
H2 effects
less dense than N2 or He (easier to breathe under pressure)
* But H2 has greater narcotic effect than He (though less than N2)
Aerobic Dive Limit:
amount of time a breath-hold animal can
dive before depletion of oxygen stores (& build-up of lactate)
Using lungs as primary oxygen store (like us) causes problems - how?
- variable buoyancy as lungs become compressed during dive
- absorption of pressurised gas into blood during dives
Methods for studying animal diving physiology
- Traditional anatomy (identifying potential adaptive structures)
- Immersion experiments on lab subjects
- Tagging individuals in the wild with data-logging sensors- can record depths, durations, surface intervals, water temp etc
- Blood samples in field after behavioural observation
- Comparative genomics (& transcriptomics on blood samples)
Pinnipeds: Hooded seals (Cystophora cristata) diving
Exhale before dives to reduce buoyancy
* Alveoli of lungs collapse under pressure during dives
* Anti-adhesive lung surfactants enable reinflation
- brain is cooled during diving by ~3 ˚C which reduces brain oxygen demand by 15-20%
Pinniped blood and vascular system
Large blood volume for body size & high haematocrit
(60% in hooded seal cf. 45% in humans)
* Large spleen also releases store of high haematocrit blood
Hooded seal myoglobin (higher o2 affinity than hb) can store 37 ml O2 kg-1
(~6x that of human muscle)
* Total O2 store of hooded seal: 90 ml O2 kg-1
Pinnibed cardio system
Peripheral vasoconstriction prioritises blood to brain & heart
(muscles run on myoglobin stores, then anaerobic respiration)
* Increased blood pressure from arterial constriction is
compensatedby brachycardia (heat slows to 4-6 beats per min)
Northern Elephant Seals)
Dive Profiles:
- Dive repeatedly to depths >500 meters for 20-25 minutes.
- Short surface intervals of 1-3 minutes.
EEG studies show they sleep briefly during dives
Northern Elephant Seals - High Blood Volume and Hemoglobin Concentration
- Blood volume: 216 ml/kg.
- Hemoglobin concentration allows 70% of total O2 store to be in the blood.
Seal Peripheral Circulation Shutdown:
- Circulation to non-essential organs shuts off during dives, conserving oxygen.
- This can cause issues like inflammation during re-perfusion after dives.
Elevated Carbon Monoxide Levels within seals:
- Maintains higher levels of carbon monoxide bound to hemoglobin, potentially protecting tissues during re-perfusion (Tift et al., 2014).
Extended Sea Periods - seals
Spend ~8 months per year at sea.
* Engage in continuous diving for foraging and predator avoidance.
Bone Structure - penguins:
Bones lack air spaces, reducing buoyancy and conserving energy.
* Strengthened bones help in propelling through the water.
* Potential carbonate reserve for buffering lactate after long dives (Ksepka et al., 2015).
Penguin diving
Lung Collapse During Dives:
* Reduces buoyancy and prevents decompression sickness.
* Rely on myoglobin in muscles for oxygen storage.
Air Bubble Release:
* Release air bubbles from plumage before jumping ashore, reducing drag and enabling acceleration
Chelonians (e.g., Turtles)
Leatherback Turtles body temp:
- Maintain body temperature through large size, insulating heat-exchange circulation, and fat layers.
Trachemys scripta (Freshwater Turtle) diving:
- Can hold breath for months during winter hibernation.
- Reduces brain metabolism to 10-15%, relying on anaerobic metabolism (Milton et al., 2006).
- Upregulates genes for neuroglobin to manage reactive oxygen species post-dive.
- Uses Heat-Shock Proteins (HSP) and SuperOxide Dismutase (SOD) to protect brain during re-oxygenation (Milton et al., 2007).
Cetaceans (e.g., Whales and Dolphins) - Genomic Adaptations:
- Comparative genomics reveal whale-specific mutations in genes for antioxidant enzymes and expanded gene families for managing hypoxia-induced reactive oxygen species
Vascular Plexus (Retia Mirabilia) - cetaceans:
Network of blood vessels that dampen pressure spikes, protecting the brain from high blood pressure during swimming (Lillie et al., 2022).
Blue Whales diving:
- Largest animal (~120 tonnes) with the largest bone (jaw mandible).
- Dive for 10-15 minutes, feeding by lunge-feeding which increases resistance (Goldbogen & Madsen, 2021).
- Reduce heart rate to ~4 bpm during descent, increase to 20 bpm during lunge-feeding, and 10-30 bpm during ascent and surface recovery.
Sound Production:
- Mysticetes: Produce vocalizations for social communication during dives, using modified larynx structures
- Odontocetes: Use nasal cavities for echolocation clicks, employing different vocal registers, including “vocal fry” for loud sound generation with minimal air volume
Buoyancy Control - cetaceans:
- Sperm whales use the spermaceti organ to adjust buoyancy: solidifying wax for descent, melting wax for ascent.
Beaked whales diving
to >1000 m, possibly to ~3000 m, feeding on deeper-living mature squid for higher calorie intake (Visser et al., 2021).
Breath-hold Diving in Hammerhead Sharks (Sphyrna lewini)
Not Air-breathers:
* Reduce blood flow to gills or close gill slits during deep dives to conserve heat.
Thermal Regulation:
* Maintain muscle temperature in cold deep waters, managing a gradient from warm surface (~26 °C) to cold depths (~5 °C) (Royer et al., 2023).
