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An interdisciplinary team of scientists using advanced imaging technology have answered the question of whether alligators share any of the same regenerative capabilities as much smaller reptiles. Many kinds of small reptiles, such as lizards, are known to regrow their tails. However, with a potential body length of 14 feet, little was known about whether alligators could possibly regrow their massive tails.
A team of researchers from Arizona State University and the Louisiana Department of Wildlife and Fisheries have uncovered that young alligators have the ability to regrow their tails up to three-quarters of a foot – about 18% of their total body length. They speculate that regrowing their tails gives the alligators a functional advantage in their murky aquatic habitats.
The team combined advanced imaging techniques with demonstrated methods of studying anatomy and tissue organization to examine the structure of these regrown tails. They found that these new tails were complex structures, with a central skeleton composed of cartilage surrounded by connective tissue that was interlaced with blood vessels and nerves. Their findings are published in the journal Scientific Reports.
"What makes the alligator interesting, apart from its size, is that the regrown tail exhibits signs of both regeneration and wound healing within the same structure," said Cindy Xu, a recent PhD graduate from ASU's School of Life Sciences molecular and cellular biology program and lead author of the paper.
“Regrowth of cartilage, blood vessels, nerves and scales were consistent with previous studies of lizard tail regeneration from our lab and others,” she said. “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.”
"The spectrum of regenerative ability across species is fascinating, clearly there is a high cost to producing new muscle," said Jeanne Wilson-Rawls, co-senior author and associate professor with ASU’s School of Life Sciences.
Alligators, lizards and humans all belong to a group of animals with backbones called amniotes. In addition to previous studies about the ability of lizards to regrow their tails, the discovery of such large and complex new tails in alligators provides considerable new information about regenerative process in the larger animal classification of amniotes.
This also leads to new questions about the history of these capabilities, and the possibilities for the future.
"The ancestors of alligators and dinosaurs and birds split off around 250 million years ago," said co-senior author Kenro Kusumi, professor and director of ASU's School of Life Sciences and associate dean in The College of Liberal Arts and Sciences.
"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.”
The researchers hope their findings will help lead to discoveries of new therapeutic approaches to repairing injuries and treating diseases such as arthritis.
“If we understand how different animals are able to repair and regenerate tissues, this knowledge can then be leveraged to develop medical therapies,” said Rebecca Fisher, co-author and professor with the University of Arizona College of Medicine-Phoenix and ASU’s School of Life Sciences.
The research team included Kusumi, Xu, Wilson-Rawls and Alan Rawls from ASU's School of Life Sciences; Ruth Elsey from the Louisiana Department of Wildlife and Fisheries; and Fisher from the University of Arizona College of Medicine–Phoenix. This research was funded by support from The College of Liberal Arts and Sciences at ASU. ASU’s School of Life Sciences is an academic unit of The College of Liberal Arts and Sciences.