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Nightmare fish may explain how our 'fight or flight' response evolved

Lampreys are the stuff of nightmares, complete with long, slimy bodies; circular mouths filled with teeth; and parasitic tendencies. But lampreys are also vertebrates, which means they have backbones and share a common ancestor with humans — and new research is revealing that we have more in common with these slippery bloodsuckers than scientists previously thought.

Lampreys belong to an ancient vertebrate lineage known as Agnatha, or jawless fish. Previous research suggests that lampreys and their relatives represent the most primitive group of vertebrates still in existence, having evolved an estimated 360 million years ago. These living fossils can give us a window into how some of our distant ancestors likely evolved.

For the last 150 years, scientists assumed that lampreys lacked a jaw because they were missing a structure known as the neural crest. This group of stem cells is unique to vertebrates, and in the womb or the egg, it develops into a wide array of structures. These structures include both jaws and the sympathetic nervous system, which controls our involuntary fight-or-flight response that kicks on in dangerous or stressful situations.

But a new study, published Wednesday (April 17) in the journal Nature, reveals that lampreys have sympathetic nerve cells after all — suggesting that the vertebrate flight-or-flight response is more ancient than scientists expected.

The new study did not begin as a search for sympathetic nerve cells.

"One of the things I love about science is that you often make discoveries by accident," Marianne Bronner, a developmental biologist at Caltech and co-author of the study, told Live Science. Instead, the work started as a search for similar cells that were precursors to the more complex neural crest seen in jawed vertebrates. They thought they might find such cells in lampreys because they are the closest thing we have to ancient jawless vertebrates that first emerged around 500 million years ago.

But when the researchers started dissecting lamprey larvae, they noticed the immature fish had structures that looked a lot like neurons running in a chain down the length of their bodies. This string of nerve cells is characteristic of a sympathetic nervous system — a system lampreys weren't supposed to have.

When the scientists looked closer, they confirmed that these structures were indeed nerves using RNA sequencing; RNA is a cousin of DNA that helps cells make proteins, in addition to serving other functions. The team also found that the cells make a precursor enzyme for noradrenaline, a key chemical messenger that helps control the fight-or-flight response.

"Now it looks like the only thing that lampreys don't have is a jaw," Bronner said.

Lampreys were previously assumed to react to danger by relying solely on pheromones given off by other lampreys. (Ecologists still sometimes use these pheromones to control the critters' movements in the lab.) The discovery that these jawless fish have a fight-or-flight response places the evolutionary origin of this system about 50 million years earlier than scientists expected.

Bronner thinks that past researchers probably missed the sympathetic nerve cells in lampreys for a couple reasons. One is that the fish have a long developmental cycle; after a young lamprey hatches, it can spend years developing in a larval stage before maturing into an adult. The sympathetic neurons may be too small to notice until late in this developmental phase, and most prior research was done on newly hatched lampreys. The new work uncovered the cells in older larvae.

Another issue is that jawless fish are far less studied in evolutionary biology than "model organisms" like fruit flies and zebrafish, which serve as a model for biological systems also found in humans. Such species are great for lab work, especially as scientists know their genomes so well. But Bronner sees huge scientific benefits in studying creatures like lampreys, too.

"Sometimes you have to go outside of your comfort zone and work on these weird animals," Bronner said — nightmare fuel and all. So the next time your adrenaline spikes when you're watching a horror movie or you've heard a twig snap in the woods, consider thanking a lamprey.

46,000-year-old worms wriggle back to life after scientists defrost them

Stone Age worms dug up from the Siberian permafrost were brought back to life after 46,000 years in suspended animation - becoming the oldest-known creatures to have existed.

The roundworms were discovered by Russian scientists inside a fossilised squirrel burrow and a deep glacial deposit near the Kolyma River in 2018, but it was unclear what they were, or how long they had been trapped in the ice.

Now genetic sequencing has shown they are an entirely new species of nematode worm which has lain dormant since the last Ice Age.

Radiocarbon dating of plant material found on the same level of the worms has shown that the frozen deposits had not thawed since the late Pleistocene.

It means they existed when Neanderthals, woolly mammoths and saber-toothed tigers still roamed the region.

The tiny worms, which are less than a millimetre in length, were thawed out and coaxed back to life in a petri dish filled with a nutritious soup designed to encourage their growth. After a few weeks in the dish, they began moving and eating. 

The worms died within a few months, however scientists said the species has reproduced and is now undergoing lab experiments.

Dr Phillip Schiffer, group leader of the worm lab at the University of Cologne, told The Telegraph: “Usually Panagrolaimus nematodes live 20-60 days.

“They instantly started reproducing and we do have a culture of these worms in the laboratory. Thus, the species is alive and we are doing experiments on it.”

Nematode worms are one of several creatures known to be able to survive harsh conditions by entering a hibernation-like state called cryptobiosis. In 2021, Bdelloid rotifers, a class of microscopic invertebrates, were found in the Arctic and brought back after 24,000 years.

Although scientists have revived single cell microbes and bacteria dating back 250 million years, it is thought to be the oldest multicellular creature ever reanimated.

Previously the longest known record for nematode worms staying in cryptobiosis was 25.5 years in the Arctic.

Prof Teymuras Kurzchalia of the Max Planck Institute of Molecular Cell Biology (MPI-CBG) in Dresden, Germany, which carried out the new research, said: “This study extends the longest reported cryptobiosis in nematodes by tens of thousands of years.

“Survival in extreme environments for prolonged periods is a challenge that only a few organisms are capable of.

“Our findings are important for the understanding of evolutionary processes because generations times could be stretched from days to millenia, and long-term survival of individuals of species can lead to the refoundation of otherwise extinct lineages.”

The tiny worms are less than a millimetre in length© Provided by The Telegraph

Genetic analysis shows the ancient worms belong to a previously unknown species, which has been named Panagrolaimus kolymaensis.

Lying dormant for decades 

The team found the species contained similar genes to other worms that can enter a state of suspended animation, including those that increase a sugar called trehalose, which may help them to survive harsh drying-out and freezing.

Experts say that the study proves that the worms can lie dormant not just for decades, or hundreds of years, but entire geological eras, waiting for conditions to improve.

Dr Vamshidhar Gade of the MPI-CBG, said: “Overall, our research demonstrates that nematodes have developed mechanisms that allow them to preserve life for geological time periods.”

Several ancient species have been revived in recent years. In 2020, Japanese and US scientists reanimated 200-million-year-old microbes found in sediments 328ft (100m) beneath the ocean floor within the South Pacific Gyre, an ocean current.

The findings do not show that life can lie waiting in the most extreme environments on Earth but gives new hope that it could be found on inhospitable planets, such as Mars and other parts of the solar system.

However, some scientists have cautioned against reanimating “time-travelling” species, warning that it could unleash ancient bugs or viruses that could threaten human health and the environment.

There are fears that global warming may cause glaciers and permafrost to melt, allowing long dormant microbes to re-emerge.

A new study in Plos by the European Commission Joint Research Centre used artificial intelligence to simulate what would happen if ancient viruses were unleashed onto modern communities.

They found that ancient invading pathogens could often survive and evolve in the modern community with 1 per cent capable of wiping out one third of the species.

The nematode study was published in the journal Plos Genetics.