Some lizards have developed strategies to regrow their docked tails, but until now little was known about the much larger American alligator’s ability to regenerate it. A team of scientists has discovered that the youngest alligators can recover part of this limb, but this differs from the original structure.
The case of the lizards, with their “removable” tails, is well known. These small vertebrates are capable of re-creating nerve cells, like other lizards, and regenerating this limb. The strategy of shedding the tail is common to escape predators, but what about much larger reptiles, such as the American alligator?
So far, it was not well documented if this crocodilian, one of the largest in the American continent, could have this ability to recover its enormous tail. A team from Arizona State University and the Louisiana Department of Wildlife and Fisheries, both in the United States, shows for the first time that the youngest specimens, caught in the wild, had recovered their tail up to 18% of the full length of their body, although they were morphologically different from the original sections.
To analyze the structure of the regenerated limbs, the scientists performed MRIs and X-rays combined with anatomical and tissue organization studies. The results, published in the journal Scientific Reports, showed that the new tails lacked skeletal muscle – unlike other lizards – and formed complex structures with a central skeleton composed of cartilage and surrounded by fibrous connective tissue intertwined with blood vessels and nerves.
“What makes the alligator interesting, apart from its size, is that the re-growing tail shows signs of regeneration and wound healing within the same structure,” explains Cindy Xu, lead author and researcher at the American university.
This overproduction of connective tissue was similar to wound healing or fibrosis in mammals, the scientists found. “We were surprised to discover scar-like connective tissue rather than skeletal muscle in the regenerated crocodile tail,” Xu adds.
The partial limb growth of these crocodiles does share similarities with the regenerated tails of New Zalanda tuataras and the regenerated limbs of adult Xenopus frogs, which have a cartilaginous endoskeleton surrounded by connective tissue without skeletal muscle.
What does regeneration contribute?
The study confirms that between the different species of reptiles and other animals, the regenerative capacity varies, and can be costly. In the case of American alligators (Alligator mississippiensis), scientists believe that regenerating their tails can give them a functional advantage when living in murky aquatic habitats.
This finding provides more information on how reptiles are the only amniotes – a group of animals with backbones among which humans are found – to maintain the ability to recover their lost limbs. “The ancestors of alligators, dinosaurs and birds separated about 250 million years ago. The study shows that the alligators have retained the cellular machinery to regenerate complex tails while the birds have lost that capacity ”, emphasizes Kenro Kusumi, co-principal author, and professor and director of the School of Life Sciences of the University of the State of Arizona . So at what point in evolution was this ability lost? So far, scientists have found no evidence of fossils of dinosaurs, whose lineage led to modern birds, with regenerated tails.
Furthermore, understanding how different animals can regenerate tissues could help develop medical therapies, according to the researchers. The team hopes that these findings will uncover new therapeutic approaches to repair injuries and treat diseases such as arthritis.