Land phenomenon grounding of whales and dolphins be due to Alzheimer’s-like cognitive deficits in pack leaders who lure their group into shallow water? A new study of brain tissue from stranded dolphins reveals pathological signs that resemble what is seen in human patients with Alzheimer’s disease.
This new research follows a landmark study carried out in 2018, which presented the first clear evidence of an Alzheimer’s-like pathology in the brain of a wild animal. Frank Gunn-Moore, co-author of the 2018 study, teamed up with Mark Dagleish of the University of Glasgow (UK) to conduct the largest survey of dementia in dolphins to date.
The brain tissues of 22 animals were analyzed, covering five different species: Risso’s dolphinsthem pilot whalesthem white beaked dolphinsthem harbor porpoises and the bottlenose dolphins. All of the animals were found stranded in Scottish coastal waters.
Three animals, belonging to three different species, presented particular pathological characteristics of Alzheimer’s disease. These included the training of amyloid plaquesthe accumulation of tangles of tau protein and the presence of a brain lesion called gliose.
Selon Gunn-Moore :
I’ve always wanted to answer the following question: are humans the only ones who suffer from dementia? Our results answer this question, as they show that the potential pathology associated with dementia is indeed not only observed in human patients.
Of course, the results cannot confirm that these animals suffered from the kind of cognitive deficits that are usually associated with dementia. They can only show that the animals develop pathological features similar to those seen in human patients with dementia.
Nevertheless, the study provides irrefutable evidence for a hypothesis often put forward to explain the mass strandings of whales and dolphins. Known as the “sick leader syndrome,” this hypothesis holds that a leader with cognitive impairment could be responsible for leading their group into shallow water, resulting in mass strandings.
This hypothesis was presented for the first time a few years ago, following the investigation carried out by a multidisciplinary team of researchers on the stranding of seven sperm whales along the Italian coast. According to this study, the whales had lost their ability to orient due to a viral infection, and a debilitating health problem in the oldest member could have dragged the group into waters that ended up trapping the animals.
In this new study (link below), the researchers hypothesize that cognitive decline linked to neurodegeneration could play a role in certain mass strandings. In humans, the study notes, the first symptoms of decline associated with Alzheimer’s disease are disorientation and confusion. It is therefore plausible to suggest that group leaders of whales and dolphins suffering from similar neurological degeneration could attract groups during strandings.
Tara Spires-Jones, a researcher from the University of Edinburgh (Scotland) working on the study, is cautious and does not want to exaggerate the results. According to her, further work is needed to explore the relationship between stranding events and dementia.
Selon Spires-Jones :
We were fascinated to see brain changes in aged dolphins similar to those of human aging and Alzheimer’s disease. Whether these pathological changes contribute to the stranding of these animals is an interesting and important question for future work.
The study published in the European Journal of Neuroscience: Alzheimer’s disease-like neuropathology in three species of oceanic dolphin and presented on the University of Glasgow website: Stranded dolphins’ brains show common signs of Alzheimer’s disease.