• Tue. Feb 27th, 2024

Secret armor of African spiny rats

Secret armor of African spiny rats

Spiny rodents produce bony plates called osteoderms under the skin of their tails, which separate when attacking the animal and give them a quick escape. Credit: Image by Edward Stanley

Unlike crocodiles, turtles, lizards, dinosaurs, and fish, which have bony plates and scales, mammals long ago swapped their ancestral armor for an insulating layer of hair.

Armadillos are thought to be the only living anomalous, boasting a resilient and resilient shell of overlapping bones. However, a new study was published in the journal iScience It unexpectedly shows that African spiny rats create similar structures under the skin of their tails, which have never been discovered before.

The discovery was made during routine CT scanning of museum specimens for the Open Vertebrate Program, an initiative to provide 3D models of vertebrates for researchers, educators and artists.

“I was scanning a mouse specimen from the Yale Peabody Museum and the tails looked unusually dark,” said Edward Stanley, director of the Florida Museum of Natural History’s Digital Imaging Laboratory.

He initially hypothesized that the discoloration was due to an imperfection introduced during the preservation of the specimen. But when he analyzed the X-rays a few days later, Stanley observed an unmistakable feature he was familiar with.

“My entire PhD was focused on osteoderm development in lizards. Once the specimen scans were processed, the tail was clearly covered with osteoderms.

Osteoderms of spiny rodents have been observed at least once, and German biologist Jochen Niethammer compared their architecture to a medieval stone slab in an article. Published in 1975. Niethammer correctly interpreted the plates as a type of bone, but his initial observations were never followed up, and the group was ignored for several decades – until scientists discovered another, apparently unrelated, feature of spiny rodents.

A Study since 2012 Apparently spiny mice can completely regenerate injured tissue without scarring, an ability common in reptiles as well. Invertebrates but was previously unknown in mammals. Their skin is particularly fragile, tearing with about a quarter of the force required to injure a normal rat’s skin. But spiny rats can heal twice as fast as their relatives.

Hoping to find a model for human tissue regeneration, researchers began mapping the genetic pathways that give spiny mice their extraordinary healing powers. One such researcher, Malcolm Madden, had a lab in the building opposite Stanley’s office.

“Spiny mice can regenerate skin, muscle, nerves, spinal cord and possibly heart cells, so we maintain a colony of these rare creatures for research,” Madden said. University of Florida and lead author on the study.

Madden and colleagues analyzed the development of the osteoderms of spiny rodents and confirmed that they were indeed similar to those of armadillos, but had evolved almost independently. Osteoderms differ from the scales of porcupines or the quills of porcupines and porcupines in that they are made of keratin, the same tissue that makes hair, skin, and nails.

There are four genera of spiny mice, all belonging to the subfamily Diominae. However, their similarities aside DNA Neither the shape of their teeth, nor a single shared feature among scientists species They are distinguished from other rodents in this group.

Suspecting that their differences might be skin deep, Stanley scanned more museum specimens from all four races. In each, he found spiny tails encased in the same sheath as the rat. The closest relatives of the Diominae – gerbils – lacked osteoderms, meaning that this trait may have evolved only once, in an earlier divergent spiny rodent ancestor.

The ubiquity of osteoderms in the group suggests that they have an important protective function. It’s not immediately clear what that function might be because of another unique attribute of spiny mice: their tails can’t be unusually detached. Tail loss is so common in some spiny rodents that up to half of the individuals in a given population show their absence in the wild.

“It was a real headache,” Stanley said. “Spiny mice can deglove their tails, which means the outer layer of skin peels away, leaving muscle and bone. When this happens individuals will often chew off the rest of the tail.

Despite the power of regeneration, tail shedding is a trick that spiny rats can only perform once. Unlike some lizards, they cannot regrow their tails and do not easily detach all parts of the tail.

The authors turned to a group of similarly exotic fish-tale geckos from Madagascar to find out why rodents, seemingly ambivalent about keeping their tails, cover them in armor. Most geckos lack osteoderms, but as their name suggests, fish-tail geckos are covered in thin, overlapping plates, and like spiny mice, they have incredibly fragile skin.

According to Stanley, the osteoderms in fish-tail geckos and spiny rodents act as a sort of escape mechanism.

“If a predator bites the tail, the armor prevents the teeth from sinking into the underlying tissue and doesn’t detach,” he said. The outer skin and its complementary bony covering are pulled away from the tail when attacked, allowing the rodent a quick escape.

Reference: Malcolm Madden, Trey Polvador, Aaron Polanco, W. “Osteoderms in a Mammal, the Spiny Mouse Acomys, and Independent Evolution of the Dermal Armor” by Brad Barbasuk and Edward Stanley, 24 May 2023 iScience.
DOI: 10.1016/j.isci.2023.106779

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