Diving is in the blood of penguins | Polarjournal
Penguins in general are perfectly adapted to a life in the water. For the hunt for krill and small fish, the animals must be able to dive also for an extended period of time. To avoid getting into respiratory distress, their blood is better able to store oxygen and release it when needed. This allows them to dive for up to 20 minutes. Picture: Michael Wenger

Penguins inspire not only by their ability to walk upright. The fact that these birds spend most of their lives in the water also fascinates both laymen and experts. Especially the diving ability of the seabirds stands out. A team of US researchers has now discovered that this ability is literally in the blood of penguins. The results of the study have now been published in the Proceedings of the National Academy of Sciences .

The team led by University of Nebraska biologist Professor Jay Storz and postdoctoral assistant Dr. Anthony Signore found in a study that the diving ability of penguins is related to the structure of hemoglobin and its ability to better bind oxygen. What was special about the study was that the team reconstructed the evolution of hemoglobin structure to show that improvements in oxygen binding must have driven diving ability. The development proceeded in two directions: On the one hand, the aforementioned structural change of hemoglobin to be able to bind oxygen even better. At the same time, however, the ability to release oxygen into tissues even under acidic conditions developed. This is particularly important because it allows the tissues that are under stress to be supplied with oxygen. So the penguins don’t run out of breath right away because they’ve exerted themselves.

The blood of penguins is very dark, because the animals have much more hemoglobin and myoglobin than, for example, humans. With the help of myoglobin, animals can store oxygen in their muscles so that they do not have to fill their lungs with air. This prevents buoyancy when diving and also prevents damage to the tissue when surfacing. Picture: Michael Wenger

The fact that penguin blood contains a lot of hemoglobin and many of the physiological processes involved in diving were already known to researchers. But in order to be able to explore the properties of haemoglobin, the team wanted to trace the evolution of the protein. “There just wasn’t a lot of comparative work on blood-oxygen transport as it relates to diving physiology in penguins and their non-diving relatives,” Anthony Signore explains. Therefore, the researchers went back in evolution about 30 and 60 million years and reconstructed the hemoglobin of the common ancestor of penguins and that of the ancestor with the closest relatives, the tube-noses (albatrosses, petrels, etc.). To do this, they first developed the protein on the computer and then spliced the gene sequences into bacteria, which then developed the two proteins. Comparison tests in terms of oxygen binding showed that the common penguin ancestor performed better than the non-diving ancestor.

Penguins take a deep breath before their dives, like all lung breathers. Oxygen is then taken up by haemoglobin and transported to the muscles, where it is stored by myoglobin and transported by haemoglobin to where it is needed. The release there depends on the pH value. The study shows that penguin hemoglobin releases oxygen depending on the acidity of the tissue, the more acidic, the faster the release. So penguins can dive longer without restrictions. Video: Michael Wenger

“It really is a beautiful system, because tissues that are working hard are becoming acidic.They need more oxygen, and hemoglobin’s oxygen affinity is able to shift in response to that acidity to provide more oxygen.”

Dr. Anthony Signore, lead author, University of Nebraska

Another problem solved by structure development is the issue of pH dependence in oxygen delivery to the target tissue. If oxygen becomes scarce there, the pH value drops and the environment becomes more acidic. This increases the demand for oxygen. But a high affinity means that the hemoglobin would be reluctant to give up its oxygen. But here the newer penguin hemoglobin surprises again: “If the pH drops by, say, 0.2 units, the oxygen affinity of penguin hemoglobin will decrease more than that of its non-diving relatives,” Signore continues. “It’s a great system because tissues that work hard become more acidic. They need more oxygen and the affinity of hemoglobin just adapts to that acidification and delivers more oxygen.” That means penguins don’t run out of air, even on long dives. Particularly in the case of emperor penguins, which are record holders for diving to depths of over 500 metres and lasting over 30 minutes, the evolution of this special blood protein has been very helpful in adapting perfectly to the ocean habitat.

Dr Michael Wenger, PolarJournal

Link to study: Signore et al (2021) PNAS 118 (13) Evolved increases in hemoglobin-oxygen affinity and the Bohr effect coincided with the aquatic specialization of penguins; DOI: 10.1073/pnas.2023936118

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