Komodo dragon lizards, new research


This 11 May 2019 video says about itself:

The Raw Nature crew observe Komodo dragons hunting in the wild during a visit to Rincah Island in Indonesia. They then demonstrate the effect of the powerful Komodo venom on a piece of raw meat.

From the Gladstone Institutes in the USA:

Komodo dragon genome reveals clues about its evolution

July 29, 2019

Summary: A new study provides the first high-resolution sequence of the Komodo dragon, as well as insight into how it evolved.

The Komodo dragons are the largest lizards in the world. These predators weighing up to 200 pounds can detect their prey from up to 7.5 miles away. And although they are cold-blooded, they can ramp up their metabolism to near mammalian levels, which gives them great speed and endurance. However, scientists have understood little about how the DNA of these remarkable lizards encodes such astounding characteristics.

Now, a new study from researchers at the Gladstone Institutes, in a close collaboration with scientists at UC San Francisco (UCSF) and Zoo Atlanta, provides the first high-resolution sequence of the Komodo dragon, as well as insight into how it evolved.

“We started the project 9 years ago to look at how genomes evolve, but to do so, we needed the genome sequences first,” said Gladstone Senior Investigator Benoit Bruneau, PhD, a senior author of the study. “At the time, other groups had sequenced the turtle genome, snake and bird genomes, and the crocodile genome was in process, but the missing branch was the varanid lizards — the family to which Komodo dragons belong.”

“I went to Komodo Island years ago as a tourist, and I saw Komodo dragons in the wild there,” said Katherine Pollard, PhD, a senior investigator and the director of the Gladstone Institute of Data Science and Biotechnology, who is the other senior author of the study. “I never would have guessed then that I would one day work on their genome. We didn’t even have a human genome at that time!”

The team studied the DNA of two Komodo dragons from Zoo Atlanta named Slasher and Rinca, whose blood samples were obtained as part of their scheduled annual check-ups.

“This project was a great opportunity for us to learn more about Komodo dragons using the newest and best technologies, and then be able to contribute our findings toward the general knowledge of lizard biology,” said Joseph R. Mendelson III, PhD, a herpetologist and evolutionary vertebrate biologist, and the director of research at Zoo Atlanta.

The study, which was published in the journal Nature Ecology & Evolution and released on BioRxiv as a preprint with a data repository, provides an extremely high-quality sequence of the Komodo dragon genome, which can now be used as a reference in efforts to sequence other vertebrate genomes.

“Vertebrate genomes are big, and they contain many repetitive sequences,” explained Pollard, who is also a professor at UCSF and a Chan Zuckerberg Biohub investigator. “Most sequencing technologies only produce short stretches of sequence at a time. When those short stretches include repetitive elements, it’s impossible to know where they belong and what they connect to, making it hard to string them together.”

To get around this problem, the team took a multi-pronged approach.

“We used multiple technologies, including long-range sequencing and a physical mapping technique to do the assembly,” said Bruneau, who is also the director of the Gladstone Institute of Cardiovascular Disease and a professor in the Department of Pediatrics at UCSF. “As a result, we have a super deep, very high-quality sequence for the Komodo.”

Once the scientists had the sequence, they used computational tools to compare it to that of other reptiles and see what makes the Komodo dragon genome unique.

Specifically, they were looking for changes in the genome that helped the Komodo dragon adapt to its environment, which have undergone an evolutionary process called positive selection. A remarkable finding was that positive selection has shaped several genes involved in the function of mitochondria, the energy powerhouses of the cell that control how well heart and other muscles function.

“Our analysis showed that in Komodo dragons, many of the genes involved in how cells make and use energy had changed rapidly in ways that increase the lizard’s aerobic capacity,” said Abigail Lind, PhD, a postdoctoral researcher in Pollard’s lab and first author of the study. “These changes are likely key to the Komodo’s ability to achieve near-mammalian metabolism.”

Lizards are generally not known for their high aerobic capacity. In other words, they become exhausted quickly after physical exertions.

“However, we know from working with Komodo dragons that they’re capable of sustained aerobic activity, which could be swimming, running, or walking extremely long distances,” explained Mendelson, who is also an adjunct associate professor at the Georgia Institute of Technology. “Our study showed us that the secret is in these mitochondrial adaptations to increase their cardiac output. This gives us an understanding of how these animals are able to do what we had been observing.”

In addition, the researchers discovered that Komodo dragons, along with some other lizards, have an unexpectedly large number of genes that encode chemical sensors known as vomeronasal receptors. These receptors are part of a sophisticated sensory system that allows animals to detect hormones and pheromones.

This type of sensing is involved in a variety of activities, including kin recognition, mate choice, predator avoidance, and hunting. In the Komodo genome, the team found over 150 copies of one class of vomeronasal receptor genes. The team also found that many of these genes are unique to each individual lizard species, raising the possibility that the Komodo dragon’s vomeronasal receptors may function in Komodo-specific ways.

“It will be interesting to determine whether this explains Komodo dragons’ ability to detect prey over such large distances,” said Bruneau. “One of the exciting things about this project is that we didn’t know what to expect. This was an opportunity to look at a genome and say, ‘Tell me the story of your organism.'”

Next, Bruneau and his team are looking forward to using their findings to investigate how genes that control the formation of the vertebrate heart have changed over the course of evolution, as most reptiles have only a three-chambered heart, while mammals have four chambers.

The completed genome sequence also represents an invaluable resource for conservation biologists interested in tracking Komodo dragons to study their ecology, and for the many scientists across the world investigating vertebrate evolution.

“The significance of this study far exceeds Komodo dragons,” said Mendelson. “It gives us a framework to compare other sequenced animals and understand the genetic basis for how all their characteristics have evolved. This project also brings to the forefront the importance of preserving biodiversity, and the important role zoos can play in broad-scale research without being injurious to the animals in our care.”

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Clever young Australian eastern blue-tongue lizards


This February 2018 video says about itself:

On this episode of Breaking Trail, Coyote catches a Blue-Tongue Skink!

While exploring the Australian outback just outside the town of Meandarra the team stumbles upon this large snake-like lizard! Infamous for their large blue tongue defensive display, this species is well known in pet trades around the world.

Get ready to meet Australia’s favorite skink!

From Macquarie University in Australia:

Baby blue-tongues are born smart

Australian research finds little lizards learn very quickly

July 15, 2019

Young Australian eastern blue-tongue lizards (Tiliqua scincoides) are every bit as clever as adults, researchers have found.

Life is hard for baby blue-tongues. As soon as they are born, they are on their own, with neither parental support nor protection. Adults of the species can grow to 600 millimetres long and enjoy the benefits of thick scales and a powerful bite, but the young are much smaller and thus more vulnerable to predation.

And that means they have to box clever if they are to survive.

A dozen adults, all over two years old, took part in the tests, along with 16 captive-born juveniles, all aged between 23 and 56 days.

“In all the tests, the young lizards performed every bit as well as the adults,” said Szabo. “This indicates that the young learn at adult levels from a very early age.”

The study, published in the journal Animal Behaviour, is the first to directly compare adult and juvenile flexible learning in a reptile species.

Frilled dragon lizards, new research


This 1 June 2019 video says about itself:

On this episode of On Location, Coyote, Mark, and Mario are in Australia! Will they be able to catch the magnificent frilled dragon during their adventure? And if so… can they snap the perfect photo of a frilled dragon on top of our Brave Wilderness Adventure Kit?! Watch to find out!

From the Université de Genève in Switzerland:

How the dragon got its frill

June 25, 2019

The frilled dragon exhibits a distinctive large erectile ruff. This lizard usually keeps the frill folded back against its body but can spread it as a spectacular display to scare off predators. Researchers at the University of Geneva (UNIGE), Switzerland, and the SIB Swiss Institute of Bioinformatics report in the journal eLife that an ancestral embryonic gill of the dragon embryo turns into a neck pocket that expands and folds, forming the frill. The researchers then demonstrate that this robust folding pattern emerges from mechanical forces during the homogeneous growth of the frill skin, due to the tensions resulting from its attachment to the neck and head.

In Jurassic Park, while the computer programmer Dennis Nedry attempts to smuggle dinosaur embryos off the island, he gets attacked and killed by a mid-sized dinosaur that erects a frightening neck frill. This fictional dinosaur [also based on Dilophosaurus] is clearly inspired from a real animal known as the ‘frilled dragon’, that lives today in northern Australia and southern New Guinea. These lizards, also known as Chlamydosaurus kingii, have a large disc of skin that sits around their head and neck. This frill is usually folded back against the body, but can spread in a spectacular fashion to scare off predators and competitors. Folding of the left and right sides of the frill occurs at three pre-formed ridges. But, it remains unclear which ancestral structure evolved to become the dragon’s frill, and how the ridges in the frill form during development.

Recycling gills

A multidisciplinary team led by Michel Milinkovitch, Professor at the Department of Genetics and Evolution of the UNIGE Faculty of Science and Group Leader at the SIB Swiss Institute of Bioinformatics, shows today that the dragon’s frill, as well as bones and cartilages that support it, develop from the branchial arches. These are a series of bands of tissue in the embryo that evolved to become the gill supports in fish, and that now give rise to multiple structures in the ear and neck of land vertebrates. In most species, the second branchial arch will eventually fuse with the arches behind it. But in the frilled dragon, this arch continues instead to expand, leading to the formation of the dragon’s spectacular frill. “These changes in the development of gill arches highlight how evolution is able to “recycle” old structures into new forms playing different roles,” enthuses Michel Milinkovitch.

Mechanical process rather than molecular genetic signal

As the frill develops, the front side of the skin forms three successive folds, which make up the pre-formed ridges. Studying the formation of these ridges, the Swiss team reveals that they do not emerge from increased growth at the folding sites, but from physical forces — whereby the growth of the frill is constrained by its attachment to the neck. This causes the top layer to buckle, creating the folds of the frill. “We then simulated this process in a computer model and discovered that we could trace how the folds develop in the frills of the real lizard embryos,” continues Michel Milinkovitch.

These results provide further evidence that physical processes, as well as genetic programs, can shape tissues and organs during an embryo’s development.