The penguin initially carries sufficient oxygen in three stores – the blood, lungs and myoglobin in muscle – to sustain aerobic metabolism. However, around 5.6 minutes after leaving the surface, lactate begins appearing in the penguin's blood and the bird crosses the so-called 'aerobic dive limit', switching to anaerobic metabolism in some tissues. So what triggers this transition?
Cassondra Williams from the Scripps Institution of Oceanography explains that the animals were thought to cross the aerobic dive limit when one of their three oxygen stores became exhausted. However, when Paul Ponganis measured oxygen levels in the blood and lungs of penguins after long dives, the animals had oxygen to spare. That only left the muscle as the potential trigger.
Williams explains that diving animals were thought to isolate their muscle from the circulatory system, leaving oxygen stored in the tissue as its only source of aerobic metabolism while submerged and forcing it to switch to anaerobic respiration once the supply was exhausted. So, she and Ponganis teamed up with Jessica Meir to travel to Antarctica to measure muscle oxygen levels in diving emperor penguin muscles and they publish their discovery that depleted muscle oxygen supplies trigger the aerobic dive limit in The Journal of Experimental Biology at http://jeb.biologists.org/content/214/11/1802.abstract.
However, before their departure, Williams had to design a near-infrared spectrophotometer to record the penguins' muscle oxygen stores as they dived in the wild. After two trying years of technical development and testing, Williams was able to travel south with her colleagues to surgically implant the spectrophotometers in the pectoralis muscles of emperor penguins. They also attached time–depth recorders to the animals' backs to track their dive profiles. Finally, the team ensured that the animals would return with their precious equipment by drilling an isolated hole in the sea ice – to which the penguins were guaranteed to return – before releasing the implanted animals to go foraging for a day or two.
After successfully retrieving all of the spectrophotometers and dive recorders and returning the penguins to their colony, Williams began analysing the data and found that the penguins had been actively foraging beneath the ice. Of the 50 dives that Williams successfully recorded, 31 exceeded the emperor penguin's calculated dive limit.
Next, Williams plotted the muscle oxygen profiles over the course of each dive and identified two distinct patterns. In the first, the oxygen levels fell continually, approaching zero around the point when the birds crossed the aerobic dive limit. Williams says, 'This profile certainly supports the hypothesis that muscle oxygen depletion is the trigger of the aerobic dive limit.'
However, when the team saw the second pattern, they were surprised that, after initially falling, the oxygen levels plateaued for several minutes before falling again to almost zero. They realised that blood must be flowing into the muscle to replenish the oxygen supply during the middle phase of the dive, delaying the onset of the aerobic dive limit.
Finally, having confirmed that the dive muscles are the source of the aerobic dive limit, Williams calculated the muscle oxygen consumption rate for dives with the first oxygen depletion pattern and was amazed to see that it was only 12.4ml of oxygen per kg of muscle per minute: 1/10th the value calculated for penguins swimming in an artificial flume and only 2 times their resting metabolic rate. 'I think this metabolic rate is impressive. You can see how hard they are working underwater but they are efficient swimmers and very hydrodynamic,' says Williams.
IF REPORTING ON THIS STORY, PLEASE MENTION THE JOURNAL OF EXPERIMENTAL BIOLOGY AS THE SOURCE AND, IF REPORTING ONLINE, PLEASE CARRY A LINK TO: http://jeb.biologists.org
REFERENCE: Williams, C. L., Meir, J. U. and Ponganis, P. J. (2011). What triggers the aerobic dive limit? Patterns of muscle oxygen depletion during dives of emperor penguins. J. Exp. Biol. 214, 1802-1812.
This article is posted on this site to give advance access to other authorised media who may wish to report on this story. Full attribution is required, and if reporting online a link to jeb.biologists.com is also required. The story posted here is COPYRIGHTED. Therefore advance permission is required before any and every reproduction of each article in full. PLEASE CONTACT firstname.lastname@example.org
Researchers target protein that protects bacteria's DNA 'recipes'
21.08.2018 | University of Rochester
Protein interaction helps Yersinia cause disease
21.08.2018 | Schwedischer Forschungsrat - The Swedish Research Council
There are currently great hopes for solid-state batteries. They contain no liquid parts that could leak or catch fire. For this reason, they do not require cooling and are considered to be much safer, more reliable, and longer lasting than traditional lithium-ion batteries. Jülich scientists have now introduced a new concept that allows currents up to ten times greater during charging and discharging than previously described in the literature. The improvement was achieved by a “clever” choice of materials with a focus on consistently good compatibility. All components were made from phosphate compounds, which are well matched both chemically and mechanically.
The low current is considered one of the biggest hurdles in the development of solid-state batteries. It is the reason why the batteries take a relatively long...
New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference
Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...
Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
17.08.2018 | Event News
08.08.2018 | Event News
27.07.2018 | Event News
21.08.2018 | Ecology, The Environment and Conservation
21.08.2018 | Life Sciences
21.08.2018 | Power and Electrical Engineering