When most animals are attacked by predators, the encounter is often fatal. However, some creatures have developed a fascinating strategy to survive these attacks – they willingly sacrifice a part of their body to escape and live another day. This remarkable ability, known as autotomy, allows certain animals to autonomously detach an appendage from their body in the face of danger.
From lizards shedding their tails to crabs or starfish relinquishing legs and arms, autotomy is a captivating survival tactic that has evolved in various species. Despite its prevalence, the mechanisms behind this rapid self-amputation remain shrouded in mystery, leaving us with a tantalizing enigma to unravel.
In a new study published in the journal Current Biology, researchers from Queen Mary University of London have unearthed a startling discovery: a neurohormone capable of inducing arm autotomy in starfish. While investigating the effects of various neurohormones on the common European starfish Asterias rubens, the scientists stumbled upon a remarkable phenomenon. Injection of a specific neurohormone caused the starfish to shed one or more of their arms.
Astonishingly, in some instances, the starfish discarded four arms, retaining only a single arm connected to the central body region housing the essential stomach. The identified neurohormone, functioning as an ‘autotomy-promoting factor,’ is a neuropeptide closely related to the human hormone cholecystokinin (CCK). In humans, CCK serves as a satiety hormone, regulating our food intake when we’re full and influencing physiological responses to stress.
Previously reported research by the esteemed research team at Queen Mary University of London revealed fascinating insights into the behavior of starfish. Their findings indicated that a CCK-type neurohormone inhibits feeding in starfish, mirroring the role of CCK as a satiety hormone in humans. Furthermore, their latest research suggests that starfish release CCK as a natural response to the stress of predator attacks.
So, as starfish indulge in their favorite meal of mussels, their feeding is abruptly interrupted when they sense danger. When caught by a predator, they exhibit incredible survival instincts by voluntarily detaching their arm, allowing them to escape and live to feed another day, albeit with one less arm.
The resilience of these fascinating creatures doesn’t end there. With astonishing regenerative abilities, starfish can grow a new arm over the course of several weeks, ultimately restoring their original complement of five arms. This remarkable behavior provides captivating insight into the intricate mechanisms of nature and the astounding adaptability of marine life.
The researchers at Queen Mary University of London were fascinated by unraveling the mechanism behind the CCK-type neurohormone and its role in triggering arm autotomy in starfish. Dr. Ana Tinoco, a key member of the London-based research group who is currently contributing to research at the University of Cadiz in Spain, provided valuable insights into their approach to addressing this intriguing question.
“We discovered that the CCK-type neurohormone is present in nerve fibers in a special muscle that is located at the base of each arm and which is known as the tourniquet muscle. As its name implies, when starfish autotomize an arm, the tourniquet muscle contracts and assists in enabling the arm to fall off whilst also closing off the wound after an arm is shed,” Tinoco explained.
“When we tested the CCK-type neurohormone for its effects on muscle in starfish, we found that it caused contraction. Therefore, we think that it triggers arm autotomy in starfish, at least in part, by being released by nerve fibers in the tourniquet muscle and causing the muscle to contract. However, our experiments indicate that it may be one of several neurohormones that work together to control the whole process of arm autotomy in starfish, which also involves breaking of ligaments that connect different parts of the skeleton as the base of the arm.”
“We think our discovery is fascinating because the ability of starfish to shed their arms is such an amazing biological phenomenon. However, it is also important physiologically because ours is the first study to identify a neurohormone that triggers autotomy in animals. We hope that this will provide the foundations of further research so that we can learn more about how autotomy works, not only in starfish but also in other animals,” said Maurice Elphick, who led the research project.
“We hope that this will provide the foundations of further research so that we can learn more about how autotomy works, not only in starfish but also in other animals. We would like to know what it is that enables some animals to autotomize and then regenerate arms or legs, whilst most animals can’t do this. Understanding the mechanisms of autotomy in animals may be useful in the field of regenerative medicine. If we can understand how some animals are able to lose and then regenerate limbs autonomously, that knowledge may be helpful in improving recovery from traumatic limb loss when it occurs in humans or domestic animals.”
Journal reference:
- Ana B. Tinoco, Vyshnavie Kirupakaran, Delia Capatina, Michaela Egertová, Maurice R. Elphick. Discovery of a neuropeptide that acts as an autotomy-promoting factor. Current Biology, 2024; DOI: 10.1016/j.cub.2024.08.003