The spiny mouse is an unassuming rodent, but it surely’s armed with a really particular tail.
CT scans present the tail is sheathed in a secret blanket of bony plates. Earlier than the scans, just one different group of contemporary mammals was identified to wield this type of armor: armadillos. The invention, reported Might 24 in iScience, might imply that the pores and skin bones are extra widespread in mammals than beforehand thought and will make clear their evolution.
The rodent’s secret was revealed when evolutionary biologist Edward Stanley of the Florida Museum of Pure Historical past in Gainesville put a museum specimen of a spiny mouse (Acomys spp.) in an X-ray machine as a part of a multi-institutional undertaking to develop 3-D digital fashions of all vertebrate life.
It was a “nondescript wanting” mouse with barely spiky fur, Stanley says. However within the preliminary X-ray, its tail appeared uncommon. “It appeared form of darkish and peculiar,” he says.
A extra detailed CT scan confirmed the mouse’s complete tail was lined in overlapping bony plates inside the pores and skin, beneath the floor layers.
To grasp how the bony plates develop, Stanley and his colleagues teamed with Malcolm Maden, a developmental biologist on the College of Florida. The staff scanned the tails of new child spiny mice up to people who had been 6 weeks previous. Bony plates kind first close to the bottom of the tail after which because the mouse ages, develop down the tail to its tip. CT scans revealed that three different species in the identical subfamily because the spiny mouse even have armor-studded tails.
These bony plates, known as osteoderms, might assist hold spiny mice and their kinfolk alive. The rodents’ pores and skin is particularly fragile and simply tears off, significantly on the tail. It’s hypothesized that the tearaway pores and skin is a macabre protection, the place attacking predators are left with a mouthful or paw stuffed with shed pores and skin. The plates might forestall predators from piercing too deep.
“In the event you can cease the enamel or the claws of your predator on the tearaway boundary, then it’s a lot simpler to get away,” Stanley explains. The mice regenerate the misplaced pores and skin later.
However the tail’s pores and skin bones would possibly shield towards extra than simply predators. For some motive, spiny mice routinely chew one another’s tails, says Ashley Seifert, a developmental biologist on the College of Kentucky in Lexington. “So possibly they’ve developed osteoderms as armament, however to defend their tails from one another as an alternative of predators.”
To raised perceive the organic underpinnings of the bony pores and skin, the researchers took pores and skin samples from the tails of new child spiny mice in locations with and with out osteoderms and analyzed gene exercise.
In pores and skin samples with osteoderms, the exercise of a set of genes related to bone cell growth was boosted in contrast with samples with out osteoderms. However the exercise of genes that make keratin, a key constructing block for pores and skin, was ramped down. The subsequent step, Maden says, is to see how all these genes really develop the osteoderms.
The analysis may assist present insights into osteoderm evolution. Bony pores and skin is present in quite a lot of reptile teams, having developed independently in crocodilians, many alternative lizard teams and a few dinosaurs (however no birds) (SN: 12/6/22). Madagascar’s fish-scaled geckos have osteoderms and shed pores and skin like spiny mice. Other than the rodents within the new research and armadillos, the one different identified mammals with bony pores and skin are all extinct: an historic hedgehog-like animal known as Pholidocercus, floor sloths and armadillo kinfolk known as glyptodonts (SN: 2/22/16).
Delving into gene exercise patterns is never accomplished in osteoderm analysis, says Chris Broeckhoven, an evolutionary biologist on the College of Antwerp in Belgium. Having this comparative knowledge from mice obtainable may yield key evolutionary insights.
One key perception, Maden says, may very well be “why [osteoderms] hold showing in evolution after which disappear.”
It’s additionally potential osteoderms are extra frequent amongst vertebrates than beforehand thought. No snakes had been identified to have the bony pores and skin after which in April researchers reported discovering them in sand boas.
These discoveries are “a very good instance of how you must have a look at the world round you,” Maden says. “Who is aware of what you’ll uncover.”