Cetaceans, the class of marine mammals that includes whales, porpoises and dolphins, are among the smartest creatures on Earth. Bottlenose dolphins, for example, have slightly larger brains than humans (1600 grams versus 1300 grams), and have also developed very complex language skills. Some dolphins have even developed tool use, which is considered a hallmark of animal intelligence.
But sometimes dolphins do rather unintelligent things, at least from a human perspective. In particular, some dolphins will beach and beach themselves on sand in a manner that often results in death. Entire pods of dolphins can do this at once.
Occasionally they do this to forage for food, a behavior known as “beach feeding,” while sometimes it’s due to pollution or industrialization. In other cases, it may be due to a “sick-leader syndrome”, in which dolphins unwittingly follow an older, confused and feeble-minded dolphin to their death.
A new study in the European Journal of Neuroscience suggests that some of this beach behavior could be due to dolphins developing Alzheimer’s disease, a progressive brain disorder that affects memory and often manifests as dementia. By analyzing the brains of 22 dolphins, researchers from the Universities of St Andrews and Edinburgh, the University of Glasgow and the Moredun Research Institute in Scotland present some of the most detailed evidence to date of this disease in dolphins. The idea that Alzheimer’s disease can affect animals beyond humans has profound implications for neurological research into the disease.
Notably, the study notes that this is not definitive evidence that dolphins can develop Alzheimer’s disease, although previous research has also pointed to the possibility. Scientists won’t know for sure unless they can test these animals for cognitive impairment. In addition, this beach behavior could be due to another factor, including naval vessel sonar.
“These are important findings that demonstrate for the first time brain pathology in stranded odontocetes [another word for toothed whales and dolphins] is similar to the brains of people affected by clinical Alzheimer’s disease,” lead researcher, Dr. Mark Dagleish of the University of Glasgow, said in a statement. “While it is tempting at this stage to speculate that the presence of these brain lesions in odontocetes indicates that they may also suffer from the cognitive impairments associated with human Alzheimer’s disease, more research needs to be done to better understand what is happening to these animals.”
When Dagleish and his colleagues dissected the brains of 22 dolphins that had died and washed up on the coast of Scotland, they found three with the same proteins and brain scars found in human Alzheimer’s patients.
Alzheimer’s is a downright terrifying disease, the exact cause of which is not fully understood. The condition is characterized by general mental decline, difficulty thinking, concentrating and understanding things, disorientation, forgetfulness, confusion and the inability to create new memories. It affects 6 million Americans, sometimes resulting in death, but experts are still not sure what causes it or how best to treat it.
One prevailing theory has to do with the buildup of proteins in the brain called beta-amyloids, which play an essential role in the growth and repair of neurons. When too many of these proteins build up in the brain, they can clump together and form amyloid plaques that disrupt communication between neurons. Think of it like the hard plaque that grows on teeth but instead accumulates on the brain.
While this is the dominant theory of what causes Alzheimer’s disease, medical science has failed to develop drugs that work against amyloid plaques, suggesting another mechanism is at play.
Nevertheless, when Dagleish and colleagues dissected the brains of 22 dolphins that had died and washed up on the coast of Scotland, they found three with the same proteins and brain scars found in human Alzheimer’s patients.
The three dolphin species were the common bottlenose dolphin (Tursiops cuts off), white-beaked dolphin (Lagenorhynchus albirostris) and a long-finned pilot whale (Globicephala melas) – which, despite its name, is a type of dolphin. Each of these specimens was older, as evidenced by worn or missing teeth, while the sample’s younger dolphins showed no signs of Alzheimer’s.
In the three with amyloid plaques, they also found another hallmark of Alzheimer’s disease: tau tangles. Tau proteins play an important role in stabilizing neurons, but as they age they can begin to clump together, forming tangles that are neurotoxic and can lodge throughout a neuron’s intracellular space. This makes communication between neurons very difficult, causing cognitive impairment.
Finding both tau tangles and amyloid plaques in dolphins are strong indicators that these marine mammals may be developing Alzheimer’s disease. But it has not yet been definitively proven. The brains of humans and dolphins are very different, and there may be other explanations for why these proteins were present in the deceased cetaceans.
Nevertheless, this research has interesting implications for the future of Alzheimer’s disease research and for marine conservation. Part of the reason we don’t fully understand Alzheimer’s disease is because we don’t have very good animal models to run experiments on, at least not anything close enough to humans. While certain animals may show similar brain damage, it may not translate to the exact same cognitive deficits.
Don’t worry, people aren’t going to test this on live dolphins because that would most likely be considered unethical. However, because dolphins are much closer to humans than rodents in intelligence, additional research in more dolphins and other marine mammals, such as baleen whales, could be helpful in understanding how Alzheimer’s disease manifests itself.
The researchers also suggested studying the lives of captive dolphins, such as those from Sea World, which have detailed life histories that “could provide a better understanding of the pathogenesis, risk factors and underlying mechanisms of [Alzheimer’s disease]’ the authors wrote.
“We were fascinated to see brain changes in aged dolphins, similar to those seen in human aging and Alzheimer’s disease,” Professor Tara Spiers-Jones from the University of Edinburgh said in a statement. “Whether these pathological changes contribute to stranding these animals is an interesting and important question for future work.”
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