African spiny mice have the same defense armor as armadillos

Mammals, for the most part, have ditched the armor-like bony plates and scales found in creatures such as crocodiles, turtles, lizards, dinosaurs, and fish. Instead, they’ve opted for an insulating coat of hair. Armadillos, boasting their unique flexible shell of overlapping bone, are considered the sole living deviation from this trend. 

However, a recent study revealed an unexpected twist – African spiny mice too, have these armor-like structures beneath the skin of their tails. This fascinating discovery has gone largely unnoticed until now.

Accidental discovery

This unexpected discovery happened rather by chance. Edward Stanley, co-author of the study and director of the Florida Museum of Natural History’s digital imaging laboratory, was performing routine CT scanning of museum specimens for the openVertebrate program. This initiative aims to create 3D models of vertebrate organisms, to aid researchers, educators, and artists.

While scanning a mouse specimen from the Yale Peabody Museum, Stanley noticed something unusual about the tails. “The tails looked abnormally dark.” He initially dismissed the discoloration, attributing it to a potential flaw that had occurred during specimen preservation. However, upon examining the X-Rays days later, he spotted a familiar feature.

With his academic background steeped in osteoderm development in lizards, Stanley recognized the peculiar structures. “Once the specimen scans had been processed, the tail was very clearly covered in osteoderms,” he said.

While this seems like a novel discovery, it is not entirely without precedent. German biologist Jochen Niethammer had noted these osteoderms at least once before in 1975. 

He likened their structure to medieval stonework and correctly inferred that these plates were a type of bone. Despite the accuracy of Niethammer’s interpretation, his observations did not garner much attention, and the group was overlooked for several decades.

Spiny mice have the ability to regenerate

This attention drought ended when researchers stumbled upon another unique trait of spiny mice: their remarkable regenerative abilities. A 2012 study illustrated that these mice can completely regenerate injured tissue without scarring, a feat unheard of in mammals but commonly found in reptiles and invertebrates. 

In addition to this, their skin is notably fragile, tearing at roughly one-fourth the force necessary to injure a common mouse’s skin. However, they can heal at a speed that is twice as fast as their relatives.

This finding sparked interest among researchers seeking a model for human tissue regeneration. They started investigating the genetic pathways behind the extraordinary healing abilities of spiny mice. Malcolm Maden, a biology professor at the University of Florida and lead author of the study, happens to work in a lab just across Stanley’s office. 

“We maintain a colony of these rare creatures for research,” said Maden, shedding light on their regenerative capabilities, which extend to skin, muscle, nerves, spinal cord, and possibly even cardiac tissue.

Maden and his team delved into the development of spiny mice osteoderms. They concluded that these structures were similar to those found in armadillos. However, they likely evolved independently. The osteoderms in spiny mice are distinctly different from the keratin-composed scales of pangolins or the quills of hedgehogs and porcupines.

Spiny mice, belonging to the subfamily Deomyinae, are categorized into four genera. Although DNA similarities and potential dental structure similarities exist, no distinct feature that sets them apart from other rodents has been identified. 

How the study was conducted

This led Stanley to further examine additional museum specimens from all four genera. In each case, he discovered the tails of spiny mice were enveloped in the same sheath of bone, a feature absent in their closest relatives, gerbils. This suggested that the trait likely evolved just once, in the ancestor of the seemingly disparate spiny mice.

The widespread presence of osteoderms in these mice suggests an important protective role. However, another peculiar characteristic of the spiny mice, their unusually detachable tails, made this role unclear. In fact, tail loss is so commonplace in some species of spiny mice that almost half the individuals of a certain population have been found to lack them in the wild.

“This was a real head-scratcher,” said Stanley. “Spiny mice are famously able to deglove their tails, meaning the outer layer of skin comes off, leaving behind the muscle and bone. Individuals will often chew off the remainder of the tail when this happens.” 

Despite their incredible regenerative abilities, spiny mice can only shed their tails once, and they can’t regrow them unlike some lizards. Additionally, not every part of the tail detaches easily.

What the researchers learned and the pieces still missing

To comprehend why these rodents, seemingly indifferent about retaining their tails, would bother to armor them, the scientists turned to an unusual group of fish-tail geckos from Madagascar for answers. These geckos, much like spiny mice, have incredibly fragile skin that sheds with the slightest provocation. They are also covered in thin, overlapping plates. Interestingly, most geckos lack these osteoderms.

Stanley proposed that the osteoderms in fish-tail geckos and spiny mice might serve as a type of escape mechanism. “If a predator bites down on the tail, the armor might keep the teeth from sinking into the tissue beneath, which doesn’t detach,” he explained. 

Therefore, when a predator attacks, the outer skin, with its complement of bone plating, pulls away from the tail, allowing the mouse a swift escape.

This remarkable discovery of armored tails in spiny mice, along with their extraordinary regenerative abilities, adds a captivating dimension to our understanding of these unique creatures. It also poses many more questions to explore about the diversity of evolutionary adaptations among mammals.

More about African spiny mice

African spiny mice, scientifically known as Acomys, are a unique group of rodents that possess several noteworthy characteristics. Native to parts of Africa and the Middle East, these mice are named for the stiff, spine-like hairs, or spines, that cover their back and part of their tail, providing them with a distinctive appearance.

The spiny coat is an adaptive feature that likely aids in predator deterrence and allows them to easily escape when caught, as the spines can come loose while the mouse slips away. Moreover, their fur color, which typically ranges from grey to reddish-brown, helps them blend into their environment, providing a degree of camouflage against predators.

In terms of behavior, African spiny mice are mostly nocturnal, coming out at night to forage for a diet that consists largely of plant material, including seeds, fruits, and stems, but they also eat insects.

What makes African spiny mice so different

What really sets African spiny mice apart from other rodents – and indeed most mammals – is their extraordinary ability to regenerate tissue. In a manner more akin to reptiles and amphibians, they can regrow skin, hair follicles, sweat glands, and cartilage after injury, without scarring. This is a very unusual trait among mammals, which typically heal wounds via scar formation.

A study published in 2012 discovered that these mice could completely regenerate tissue that was removed from their ears – an ability not found in common mice. Additionally, they can heal small wounds in as quickly as three days, whereas it could take common mice up to two weeks to heal the same type of injury.

The remarkable regenerative capacity of the African spiny mice has sparked interest among scientists seeking to understand the underlying mechanisms and genetic factors responsible. Such knowledge could potentially be harnessed for medical applications, including tissue regeneration in humans.

Other intriguing characteristics

Another intriguing feature about the African spiny mice, as discovered in a recent study, is the presence of bone-like structures, or osteoderms, beneath the skin of their tails. This characteristic, which had been overlooked until the study was conducted, is similar to the protective adaptation found in animals like armadillos and some lizards.

However, spiny mice have an unusual tendency to shed their tails – a trait known as autotomy – to escape from predators. Unlike some lizards, these mice can’t regrow their tails, adding another layer of peculiarity to their many unique characteristics.

In sum, African spiny mice are not just interesting because of their spiny hairs but also due to their exceptional healing abilities and their recently discovered osteoderms. These features make them a fascinating subject for researchers interested in evolutionary biology and regenerative medicine.

More about armadillos

Armadillos are a unique group of mammals known for their distinctive armored shells. They are part of the family Dasypodidae, and are predominantly found across the Americas, with species ranging from the southern part of North America all the way to Argentina in South America.

The name “armadillo” originates from Spanish and translates to “little armored one,” which is a fitting descriptor for their most prominent feature: the hard, protective shell, or carapace, covering their back, head, legs, and tail. This shell is made of bony plates, called scutes, that are covered by a leathery skin, giving armadillos an appearance that is quite unlike most other mammals.

Armadillos vary significantly in size, ranging from the small pink fairy armadillo, which is about 5-6 inches long, to the giant armadillo that can reach up to 5 feet in length when you include its tail.

These animals are typically nocturnal and have poor vision, relying instead on their excellent sense of smell to navigate and find food. Most armadillos are insectivores, with a diet that consists primarily of ants, beetles, termites, and other insects, but some species also consume plants, fruits, and small vertebrates.

Armadillos have a few remarkable abilities

Armadillos are also known for their remarkable digging abilities. They use their sharp claws to dig for food and to create burrows for shelter. These burrows serve as a refuge from predators and extreme weather conditions.

When it comes to self-defense, apart from their protective shell, some species of armadillos, like the three-banded armadillo, can roll themselves into a hard armored ball to thwart predators. Others might opt to run, dig, or even leap into the air to startle potential threats.

Armadillos have a peculiar reproductive trait as well. The nine-banded armadillo, for instance, gives birth to identical quadruplets every time it reproduces, the result of a single fertilized egg splitting into four.

Used in leprosy research

In terms of scientific and medical interest, armadillos have been used in leprosy research for many years because they, unusually among mammals, can contract the disease. This led to some significant breakthroughs in our understanding of the condition.

However, it also means that there’s a small risk of transmission to humans, particularly those who handle armadillos regularly.

In conclusion, armadillos are fascinating creatures known for their armored bodies, digging abilities, and unique reproductive strategies. They’re a testament to the diversity of adaptations among mammalian species.

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