New theory on why dolphins beach themselves

‘Cetacean stranding’ is the technical term for beached whales and dolphins. They normally die because of dehydration or collapsing under their own weight and they might end up drowning when high tide covers their blowholes.

There have been several theories as to the cause. If a single animal beaches it is normally the result of sickness and injury. Contributing factors could be bad weather, navigation errors, old-age or hunting too close to shore.

Beached dolphins
Beached dolphins. Image: IFAW. One Green Planet.

New theory – Alzheimer’s

A new theory, the conclusion of a study co-authored by Prof Frank Gunn-Moore of the University of St Andrews, suggests that dolphins may become stranded in shallow waters because they follow leaders suffering from a condition similar to Alzheimer’s disease in humans.

The scientists analysed the brains of dolphins beached on Scotland’s shores. They found changes in the brain similar to the changes that are found in the brains of people with Alzheimer’s, the most common type of dementia.

The theory, then, is that the leader of a dolphin pod, leads their healthy followers into dangerously shallow waters because they become confused and/or lost through their mental illness.

The lead author of the study, Dr. Mark Dalgleish, of the University of Glasgow, said:

“This still needs to be investigated, but if a parallel condition exists in dolphins, it could certainly explain some mass strandings.”

In humans, Alzheimer’s disease results in “biological hallmarks” which include abnormal clusters of sticky proteins in the brain. These are known as amyloid plaques.

A pilot whale and two dolphins that beached and died on the Scottish coast were found to have amyloid plaques. In addition, they had a protein called phosphorylated tau. This is another sign of the disease.

And they saw other features of dementia including gliosis which involves a change in cell numbers in response to central nervous system damage.

The researchers couldn’t tell if the dolphins suffered cognitive decline which is part of the diagnostic process of assessing Alzheimer’s disease in humans. However, the biological changes in the brain are consistent with this degenerative condition.

Dalgleish also said:

“These are significant findings that show, for the first time, that the brain pathology in stranded odontocetes – toothed whales including dolphins – is similar to the brains of humans affected by clinical Alzheimer’s disease.”

He added:

“While it is tempting at this stage to speculate that the presence of these brain lesions in odontocetes indicate that they may also suffer with the cognitive deficits associated with human Alzheimer’s disease, more research must be done to better understand what is happening to these animals.”

This new research which has been published in the European Journal of Neuroscience looked at more species than previously was the case and found further signs of Alzheimer’s disease. There is no cure for Alzheimer’s although in humans it’s progress can be slowed with a drug which clears the brain of amyloid.

Summary of the ‘abstract’ (summary) to the study (a reworking to simplify it). This is technical as expected

The study discusses the occurrence of Alzheimer’s disease (AD)-like neuropathology in the brains of odontocetes, which are a group of toothed whales. AD is a neurodegenerative disease that is characterized by the accumulation of amyloid-beta plaques and hyperphosphorylated tau protein in the brain, as well as gliosis (an increase in the number of glial cells).

The abstract notes that the brains of 22 stranded odontocetes of five different species were examined using immunohistochemistry, and that all of the aged animals showed accumulation of amyloid plaque pathology.

In addition, in three animals of three different species of odontocete, there was co-occurrence of amyloid-beta plaques, intraneuronal accumulation of hyperphosphorylated tau, and other AD-like neuropathological changes.

One animal showed similar changes, but without amyloid plaques. The abstract also mentions that microglia and astrocytes were present in all of the brain samples examined, but that there were differences in their numbers and appearance between individual animals.

The presence of AD-like neuropathology in these odontocetes suggests that they may be susceptible to AD, although the significance of this pathology in terms of the health and death of the animals is not known.

The study also suggests that this pathology may contribute to the cause of unexplained live-stranding events in some odontocete species and support the “sick-leader” theory, which proposes that healthy conspecifics in a pod may strand due to high social cohesion.

Study title: Alzheimer’s disease-like neuropathology in three species of oceanic dolphin. LINK.

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