Why Do Whales, Dolphins and Porpoises Beach or Strand Themselves?

Whales and their relatives are intelligent animals. Many use echolocation (the emission of sound waves and the analysis of the reflected sound) to enable them to navigate even when the visibility in the ocean is poor. It's therefore very puzzling that whales, dolphins and porpoises sometimes swim on to a beach and strand themselves. The urge to reach the beach is so strong that if the animals are moved into the water, they often head back to the beach to face almost certain death. Although cetaceans are mammals and breathe air like us, their bodies are damaged without the buoyancy of water to support them. Starvation and dehydration also contribute to their death on land.

A killer whale and a calf - photo by Christopher Michel,
CC BY-2.0 License

Beaching of cetaceans (whales, dolphins and porpoises) has occurred since at least the time of Aristotle, so it's probably a natural part of their biology. It's possible that human activity is increasing the incidence of beaching today, though, which is one reason why it's important to know the causes. It's heartrending to see sentient animals in distress and dying on a beach. In addition, if a large group of animals beach themselves, or if beaching occurs frequently, the animal's population size may be adversely affected.

Beaching of single animals is generally due to the fact that the animal is sick and can longer swim or because a baby has lost its mother and is too weak to fight ocean currents. Mass beachings or strandings are harder to explain.

In many cases today, investigators never discover why a group of cetaceans beach. Sometimes there are clues, however. Occasionally the animals' bodies show injuries that suggest that they have recently been attacked by sharks or other cetaceans. They may be trying to escape the danger. In other cases, tests show that the whales are infected by parasites or viruses, which may affect their navigation system and cause them to become disoriented, Many cetaceans are very social animals and have close bonds with other members of their group. If one or more animals in a group beach, the others may follow because they don't want to be separated from their companions or their leader.

Beached false killer whales - photo by Bahnfrend,
CC BY-SA 3.0 License

There have been suggestions that military sonar interferes with the navigation system of cetaceans and causes beaching. High intensity sonar has been found to cause bleeding in the brains of cetaceans. Another suggestion is that beached cetaceans have been confused by magnetic field anomolies. There is no direct evidence for this, but a substance called biomagnetite has been found in the brains of some whales. It's known that some animals use this substance to detect the Earth's magnetic field and to navigate. However, we have biomagnetite in our body, too. The role of biomagnetite in whales and in humans is far from clear.

If one cetacean beaches and if that animal is small or is a youngster of a big species, it may be possible to save the animal if a rescue facility is nearby. When a big animal or many animals are stranded, it's harder to help them. It's sometimes possible to move stranded animals back into the water if they're not too big, but they may beach themselves again. One argument against moving the animals into the water is that if they've beached themselves because they're sick, when they're back in the ocean they may infect other animals. We really need to discover the causes of beaching for the sake of the world's cetaceans.

Malaria Parasite Alters Body Odour of Mice to Attract Mosquitoes

A mosquito feeding on human blood; photo by the CDC

Researchers have discovered that the malaria parasite has a very useful technique to help it complete its lifecycle, at least in mice. The parasite alters the body odour of a mouse, making the animal more attractive to the mosquitoes that the parasite needs for the next stage of its life cycle.

Malaria parasites belong to the genus Plasmodium and are microscopic, single-celled protozoans. The genus affects other mammals, birds and reptiles as well as humans. Five species of Plasmodium are known to cause malaria in humans. As in humans, the malaria parasite that infects mice needs two hosts to complete its complex life cycle - a mouse and a mosquito.

The research concerning Plasmodium and body odour was performed by scientists from Pennsylvania State University and ETH Zurich. The researchers used both infected and uninfected mice in their investigation, which lasted for 45 days. They found that the infected mice emitted a unique ratio of odiferous chemicals from their body compared to the uninfected mice. The identity of the chemicals didn't change, but their ratio did. The change was especially noticeable when the infected mice were showing no symptoms of the infection. This was the critical stage when the malaria parasite needed to enter a mosquito in order to continue its life cycle.

Stages of the life cycle of Plasmodium, stained;
photo by the CDC

The assumption is that the presence of the malaria parasite is somehow responsible for the altered body odour produced by a mouse, but how this happens isn't yet known. It would be very interesting to discover the mechanism involved!

The researchers don't yet know if malaria parasites can alter our body odour, too, but they plan to investigate this. They say that if our odour does change, the alteration could be detected and used as a non-invasive test to identify people who have apparently recovered from malaria but are still infectious. These people could then be treated for the disease.

Malaria is a very unpleasant illness and can be deadly. It's a major problem in some countries. Any method to help reduce its spread would be useful.

Tibetans Can Live at High Altitude Due to a Denisovan Gene

Living at high elevations causes problems for most of us, but not for Tibetans. Researchers say that this is because they have inherited a helpful gene from extinct relatives of modern humans known as Denisovans.

Our red blood cells contain hemoglobin, a molecule that carries oxygen from our lungs to our tissues. When someone who normally lives at low elevation travels to a higher elevation to live, their body makes more red blood cells and more hemoglobin to compensate for the reduced oxygen level in the air. This enables their body to obtain the oxygen that they need, but it can also make their blood thicker. The thickened blood can lead to hypertension or a heart attack.

A Tibetan yak; photo by Dennis Jarvis,
CC BY-SA 3.0 License

Tibet is a high plateau region in China. The people of Tibet have an increased red blood cell and hemoglobin concentration in their blood compared to people living at lower elevations, yet most don't experience the health problems linked to this state. Researchers from the University of California, Berkeley, say that they have found the answer to this puzzle.

The Denisovans were a member of the genus Homo that became extinct 50,000 to 40,000 years ago. Although only a few Denisovan bones have been discovered, both nuclear and mitochondrial DNA have survived, enabling a fascinating analysis of Denisovan genes.

A human gene known as EPAS1 is responsible for the increase in concentration of red blood cells and hemoglobin at high elevations. The gene exists in several variants, or alleles. Most people have a variant that produces a strong effect at high elevations and can indirectly lead to health problems. The Chinese population contains a variant that is very different from that possessed by other humans (as far as is known) and is very similar to a Denisovan gene. This variant increases the red blood cell and hemoglobin level only slightly, enabling survival at high elevations without cardiovascular problems. The useful variant is present in 87% of Tibetans today, who live at high elevation, and in only 9% of Han Chinese people, who live at lower elevations. The two groups share a common ancestor.

The researchers theorize that long ago Denisovans and modern humans who had traveled to China from Eurasia interbred, supplying the modern humans with the EPAS1 variant. This variant was advantageous for the Chinese people who chose to live at a high elevation and spread through the population. It's an interesting idea. It will also be very interesting to learn more about the Denisovans and to discover if they had other effects on our genome.