Young American alligators (Alligator mississippiensis) have the ability to regrow their tails up to 18% of their total body length, according to a study published in the journal Scientific Reports. The study authors hope their findings will help lead to discoveries of new therapeutic approaches to repairing injuries and treating diseases such as arthritis.
Xu et al. present the first anatomical and histological evidence of tail repair with regrowth in an archosaur, the American alligator (Alligator mississippiensis); the regrown alligator tails constituted approximately 6-18% of the total body length and were morphologically distinct from original tail segments. Image credit: Norbert Nagel / CC BY-SA 3.0.
“What makes the American alligator interesting, apart from its size, is that the regrown tail exhibits signs of both regeneration and wound healing within the same structure,” said fist author Dr. Cindy Xu, a researcher in the School of Life Sciences at Arizona State University.
“Regrowth of cartilage, blood vessels, nerves, and scales were consistent with previous studies of lizard tail regeneration from our lab and others.”
“However, we were surprised to discover scar-like connective tissue in place of skeletal muscle in the regrown alligator tail.”
“Future comparative studies will be important to understand why regenerative capacity is variable among different reptile and animal groups.”
Dr. Xu and colleagues used advanced imaging techniques combined with demonstrated methods of studying anatomy and tissue organization to examine the structure of the regrown alligator tails.
They found that the new tails were complex structures with a central skeleton composed of cartilage surrounded by connective tissue that was interlaced with blood vessels and nerves.
“The spectrum of regenerative ability across species is fascinating, clearly there is a high cost to producing new muscle,” said co-lead author Dr. Jeanne Wilson-Rawls, also from the School of Life Sciences at Arizona State University.
The regrown alligator tail is different from the original tail; regrown scales are densely arranged and lack dorsal scutes (top right); an unsegmented tube of cartilage (yellow) replaces bone (tan) in the regrown tail; moreover, the regrown tail lacks skeletal muscle (red) and instead, there is an abundance of fibrous connective tissue (pink). Image credit: Arizona State University.
Alligators, lizards, and humans all belong to a group of animals with backbones called amniotes.
While the team previously studied the ability of lizards to regenerate their tails, the new finding of regrowth of complex new tails in the alligator gives further information about the process in amniotes.
“The ancestors of alligators and dinosaurs and birds split off around 250 million years ago,” said co-lead author Professor Kenro Kusumi, also from the School of Life Sciences at Arizona State University.
“Our finding that alligators have retained the cellular machinery to regrow complex tails while birds have lost that ability raises the question of when during evolution this ability was lost.”
“Are there fossils out there of dinosaurs, whose lineage led to modern birds, with regrown tails?”
“We haven’t found any evidence of that so far in the published literature.”
“If we understand how different animals are able to repair and regenerate tissues, this knowledge can then be leveraged to develop medical therapies,” said co-author Professor Rebecca Fisher, a researcher in the School of Life Sciences at Arizona State University and the Department of Basic Medical Sciences at the University of Arizona College of Medicine-Phoenix.
C. Xu et al. 2020. Anatomical and histological analyses reveal that tail repair is coupled with regrowth in wild-caught, juvenile American alligators (Alligator mississippiensis). Sci Rep 10, 20122; doi: 10.1038/s41598-020-77052-8