Tag Archives: alligator

Alligators can regrow their tails, and it could help us heal our own wounds better

Young alligators sometimes lose their tails, but they can grow them back to a certain extent, a new study reports. Each animal can regrow around three-quarters of a foot of tail, roughly equivalent to one fifth of their total body length.

Image via Pixabay.

The team used advanced imaging techniques to determine whether alligators have the same type of regenerative tissues known in smaller species of reptiles. Lizards, for example, have evolved to have detachable tails that can regrow, which they use to escape predators. But alligators are very large animals, potentially reaching up to 14 feet, and it was unknown how that difference in scale reflects on their regenerative abilities.

Taily tales

“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 Arizona State University’s (ASU) School of Life Sciences.

“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, 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.”

Alligators and humans both belong to the amniote group, related species who all have a spine or backbones. Lizards do, as well. Understanding more about the natural regeneration processes of these species could point the way towards better ways of repairing our own bodies after damage.

By studying the anatomy and tissue organization of regrown alligator tails, the team found that they were made up of a central skeleton of cartilage surrounded by connective tissue. The tails were fully irrigated with blood vessels and had nerve bundles, meaning they were fully-functional tails. The sheer scale and complexity of these regrown body parts after were surprising, the team adds, and goes a long way towards our understanding of regeneration processes in larger amniotes. It also raises questions about the history of such processes, and about their possibilities in the future.

For example, the team notes that alligators and birds both split off from dinosaurs around 250 million years ago, but birds lost their ability to regenerate while alligators did not. We’re not exactly sure when, or why, this happened. The authors note that existing literature makes no mention of dinosaur fossils with regrown tails.

But perhaps of more immediate concern for most of us is whether the findings have practical use. The team says it lays the groundwork for new therapies meant to heal wounds or treat 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 of the paper.

The paper “Anatomical and histological analyses reveal that tail repair is coupled with regrowth in wild-caught, juvenile American alligators (Alligator mississippiensis)” has been published in the journal Scientific Reports.

Alligator found sunbathing on an ocean beach in Florida. Credit: Duke University.

Why alligators on the beach and killer whales in the river is the new normal

Alligator found sunbathing on an ocean beach in Florida. Credit: Duke University.

Alligator found sunbathing on an ocean beach in Florida. Credit: Duke University.

Recently, more and more peculiar sightings of predators have been reported in places they’re not traditionally associated with. For instance, alligators have been spotted enjoying the sun on Florida beaches while killer whales have been seen swimming freely in freshwater rivers. At first glance, these shocking occurrences can be explained by successful conservation efforts that have improved predator populations — but there’s much more to it.

In a new study, researchers have found that as predator numbers rebounded, they’ve actually reclaiming what was rightfully theirs, reconquering habitats they called home before human activity drove them out.

“We can no longer chock up a large alligator on a beach or coral reef as an aberrant sighting,” said Brian Silliman, Rachel Carson Associate Professor of Marine Conservation Biology at Duke’s Nicholas School of the Environment.

“It’s not an outlier or short-term blip. It’s the old norm, the way it used to be before we pushed these species onto their last legs in hard-to-reach refuges. Now, they are returning.”

Home away from home

Silliman was once in a saltmarsh studying crabs and snails when he came across an alligator, which is a freshwater specialist. He was utterly shocked but as he learned of other similar sightings, the biologist spotted a pattern. Soon, it was clear that the alligators weren’t alone and that other apex predators, both on land and in water, were unconventionally moving into new territories.

By processing data from scientific studies and government reports, Silliman and colleagues learned that large predators were spotted into other territories. Examples include the movements of orangutans into disturbed forests, river otters into marine wetlands, wolves and coyotes onto beaches and rocky shores, and grey, harbor, and harp seals from the Arctic into subtropical waters. These places were actually part of the predators’ original habitat but human intervention drove them out, Silliman says.

“The assumption, widely reinforced in both the scientific and popular media, is that these animals live where they live because they are habitat specialists. Alligators love swamps; sea otters do best in saltwater kelp forests; orangutans need undisturbed forests; marine mammals prefer polar waters. But this is based on studies and observations made while these populations were in sharp decline. Now that they are rebounding, they’re surprising us by demonstrating how adaptable and cosmopolitan they really are,” Silliman said, who published the findings in the journal Current Biology.

The findings are good news. They suggest that large predators are more adaptable than previously thought. For instance, up to 90 percent of the diets of alligators found in seagrass or mangrove ecosystems consisted of stingrays, sharks, shrimp, and other marine species. As climate change intensifies, it’s important to know that some predators are more resilient than previously thought in order to plan conservation accordingly.

Climate change, for instance, threatens kelp forests which sea otters love but the animals are flexible enough to occupy estuaries which lack kelp forests. Moreover, the movement of large predators back into their historic ranges can be beneficial for ecosystems. The introduction of sea otters to estuarine seagrass beds helps protect the beds from being smothered by epiphytic algae that feed on excess nutrient runoff from inland farms and cities.

“It tells us these species can thrive in a much greater variety of habitats. Sea otters, for instance, can adapt and thrive if we introduce them into estuaries that don’t have kelp forests. So even if kelp forests disappear because of climate change, the otters won’t,” Silliman said. “Maybe they can even live in rivers. We will find out soon enough.”

Breeding birds use alligators to protect nests from egg-eaters

Breeding birds and alligators have developed an unlikely partnership, where the birds build their nests on alligator territory for protection.

American alligator, photo by Hans Stieglitz.

For many bird species, nest predation is one of the biggest threats. An association between bird nests and alligators had been reported before, but researchers proposed it’s alligators that like to stick around nests, eating dropped chicks, which are chicks ejected from the nest when a bird lays more eggs than they can raise. Lucas Nell from the University of Florida and colleagues believe it’s the other way around.

In this study, the authors compared the body condition of ~40 female alligators living with and without long-legged wading bird nesting colonies in similar habitat in the Everglades, Florida. They found that alligators living close to nests exhibited better body condition, and propose that they actually feed on mammals attempting to eat the birds’ eggs.

“Our study is the first to demonstrate a mutually beneficial relationship between nesting birds and a crocodilian: nesting wading birds provide nutrition for alligators that, by their mere presence, create predator-free space for birds. Crocodilians and nesting birds co-occur throughout the tropics, so these may be globally important ecological associations.”

They also found that the body condition of alligators found near wading bird nesting colonies was higher than those in similar habitat without active colonies, independent of a range of environmental variables. This doesn’t rule out alligators feeding on ejected chicks, but it seems to indicate that the interaction is much more complex than previously thought.

Crocodilians use sticks to attract prey

  • Two distinct groups of crocodilians have been reported to use tools for hunting
  • They balance sticks on their snouts, baiting birds who want to use the sticks for nests
  • Crocodiles actively search for the sticks (which are usually rare) and do this more often during the birds’ mating season

Mugger crocodile (Crocodylus palustris) at Madras Crocodile Bank, Tamil Nadu, India, with sticks on its head. Image credits: Dinets et al. (2013).

It’s been known for quite a while that the usage of tools isn’t restricted to humans. Monkeys (of course) also use tools, but this type of behavior has also been reported in other species, including crows, dolphins, elephants and otters. Now, a new study has reported that crocodiles and alligators also use sticks to attract prey.

In recent years, reptile research has provided some stunning results, showing that they are not only cold-blooded efficient killers, but that they exhibit a myriad of remarkable behaviors. Play behaviour, complex social interactions, gaze recognition, pair-bonding and monogamy, social hunting, speedy learning abilities and good memories – they have all been reported in reptiles.

Now, another very interesting unexpected adaptation has been demonstrated across these groups: tool usage.

As described by Dinets et al. (2013), Mugger crocodiles Crocodylus palustris in India and American alligators Alligator mississippiensis in the USA have been observed to lie, partially submerged, very close to birds they want to hunt, with sticks balanced carefully on their snouts. Birds want to take the sticks to use them in their nests and… let’s just say it usually has a very bad ending for the birds.

But what’s remarkable is that this occurrence of stick usage by crocodilians isn’t random! Stick displaying took place consistently more often with crocodiles living closer to rookeries, and it also took place more often during mating season – when birds are more inclined to construct nests. It’s also noteworthy that sticks are pretty rare in this type of environment – the reptiles actively search for them, especially during the birds’ mating period.

Baiting behavior was demonstrated before in archosaurs (the big group of species which includes crocodiles, birds and all extinct dinosaurs). Green herons (Butorides virescens) often do it: they use feathers, twigs and even berries and bits of bread to attract fish, while burrowing owls (Athene cunicularia) use mammal dung to attract dung beetles. Also, anecdotal reference suggests that crocodiles also use fish fragments to attract birds. But the fact that this has been consistently reported in two separate groups seems to suggest that this type of behavior is mainspread.

If you think about it, crocodiles have been around for over 70 million years – since the Cretaceous. They are incredibly well adapted to the environment, being able to live as scavengers and survive for months without food. They can even go into a state of hibernation when conditions aren’t favorable, waking up when things are looking up. So it makes sense that they learned a trick or two about hunting.

Each bump on the crocodile or alligator's face is barely a millimeter wide and has the shape of a dome. (c) :Leitch & Catania.

Crocodile skin around its jaws is 10 times more sensitive than that of human fingertips

Considering their heavy scale armor, and ferocious apatite, “sensitive” might not be the first adjective that comes to mind when describing crocodiles or alligators. A new study has sought to answer a long lasting riddle for biologists after it finally found the purpose of peculiar black spots or domes on crocodile and alligator heads. Apparently, these act as extremely sensitive sensors, that can sense touch or pressure 10 times better than the skin of a human’s fingertip.

Some 4000 such dots are present on alligator heads, particularly along their jaws, inside their mouths, and between their teeth. Crocs are even more gifted, as they also have dome sprinklings over parts of the rest of their bodies, thus amounting to 9000 dots in total. These formations were first described over a century ago and have since been known as integumentary sensory organs, or ISOs.

Despite scientists have known for a very long time that the domes pose a sensing function of some sort, the exact purpose and functionality has escaped them. Many studies have argued that these might act like salt sensors, helping crocs and alligators detect unsafe to drink water, or used to detect faint electrical signals given off by prey. No evidence has been provided, however.

Each bump on the crocodile or alligator's face is barely a millimeter wide and has the shape of a dome. (c) :Leitch  & Catania.

Each bump on the crocodile or alligator’s face is barely a millimeter wide and has the shape of a dome. (c) :Leitch & Catania.

Vanderbilt University grad student Duncan Leitch, along with his adviser biologist Ken Catania, took it upon themselves to provide an answer to this puzzling question. Leitch first took a croc-handling course – a baby croc-handling course that is – and order relatively small alligators from refuges and crocodiles from commercial breeders.

Bumps that turn the croc and alligator into perfect on the sly predators

When he cut away the domes, he uncovered a vast network of nerve endings, including touch receptors tuned specifically to pressure and vibration. He then tested the various other theories presented in studies that sought to define the ISOs function. The animals were inserted in saltwater of varying degree, but the ISOs nerve endings didn’t react. Then, a 9-volt battery was dipped into the water to create an electric field, but again nothing back at the croc’s end. Both leading theories were busted.

Instead, Leitch found that the nerves feeding into the ISOs end in a variety of touch sensors, after he found the domes responded to stimuli from von Frey filaments—hairlike, standardized wires used to gauge sensation levels. Actually, the black dotes on the animals’ faces are so sensitive that they can detect pressure too slight even for the filaments.

“My professor and I didn’t believe at first that they could be that reactive,” Leitch said. “We closed our eyes and tried to tickle each other with [the filaments] on our fingertips, and neither of us could even feel it.”

Ten times more sensitive than our fingertips

The researchers found that the most sensitive ISOs can sense forces as tiny as 78 millionths of a Newton or  10 times more sensitive than the most sensitive parts of our fingertips. This explains how crocs and alligators are able to detect ripples from even a single drop of water-and therefore even very weak prey movements, a theory for ISOs function first mentioned in 2002. To put the theory to the test, Leitch  dropped pellets of food into the still tiny animals’ water tanks, all while in pitch black. He found that the crocs would almost instantly turn towards the food was, heads towards it, and bite it within 50-70 milliseconds after their skin touched it.

“This was exactly what I had hoped somebody would do with ISOs, in terms of really looking at the distribution and the electrophysiology, because that’s really the way to answer these questions about function in a tiny sense organ like this,”  said Kent Vliet, co-chair of the Association of Zoos & Aquariums’ Crocodilian Advisory Group.

The sensors aren’t only used for feeding, though. A great proportion of these domes are present inside the animals’ mouth, between teeth especially. These would most likely serve to offer sensitivity to the mout to help their young out of their shells and to hold the offspring between their jaws for protection.

Next the researchers plan on studying why crocs also have these bumps on their bodies, not just their faces. Some people have speculated that the alligators have body ISOs buried deeper in their skin, but Leitch saw no evidence.

“What’s interesting to me is that such a scaly animal, one that’s so heavily armored, could have a sensitivity that rivals or surpasses our tactile abilities,” Leitch said. “But they have all these little tactile areas that are so exquisitely sensitive—it seems really amazing.”

Findings were published in the Journal of Experimental Biology.