As sufferers of post-traumatic stress syndrome know all too well, frightening experiences can be strong, long-lasting and notoriously difficult to erase. Now, we’re starting to understand why. Far from trying to purge these memories, the brain actively protects them by hiring a group of molecular bodyguards called CSPGs (or chondroitin sulphate proteoglycans in full).
By studying the brains of rats, Nadine Gogolla from Harvard University found that CSPGs – large chains of sugars and proteins – accumulate in the space around nerve cells and form defensive nets around a select few. Dissolve these nets, and the rats’ fearful memories were more easily erased.
The nets start to form round about the time when rats reach adulthood and their fearful memories become harder to erase. As adults, rats can learn to be scared of an inoffensive sensation, like the sound of a buzzer, for the rest of their lives, if it’s paired with an unpleasant one, like an electric shock.
However, the strength of this terror starts to wane if the rats repeatedly hear the ominous buzz without any nasty consequences. This process is called extinction, but it’s nowhere near as permanent or robust as the creation of the original fear. The minute the shock returns, the fear response recovers. This happens so quickly that the memory clearly hadn’t been erased or overwritten – the rat had merely learned to block it out.
Things are different in puphood. Before their third week of life, a rat’s fear memories can be easily erased; only afterwards do they become indelible. Gogolla thinks that the nets are the reason why. She looked at the brains of baby rats in their first month of life, and focused on their amygdala, a pair of almond-shaped structures that have roles in processing emotions. The number of CSPG nets in these regions shot up as the days went past, but particularly in the third week, when the switch from erasable fear memories to permanent ones takes place. That’s no coincidence.
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science.
Twenty-two thousand sounds like a huge number. It’s happens to be number of eastern Pacific gray whales currently swimming off the coast of North America. It’s certainly much larger than 140, the number of whales that aboriginal people of this area are allowed to hunt. And it’s far, far bigger than zero, the population size that the whales were rapidly approaching in the mid 20th century.
Obviously, it’s all relative. Twenty-two thousand is still much less than ninety-six thousand. That’s the size of the original gray whale population and it’s three to five times the current count. Not exactly cause for conservational complacency, then.
Previously, conservationists and whalers alike could only speculate on the number of whales that lived before their flirtation with extinction. But now, Elizabeth Alter and Stephen Palumbi from Stanford University have managed to pin down a figure by looking at the genetic diversity of living whales. And their results suggest that despite a rebound that Hollywood would envy, the grays are still a pale shadow of their former strength.
The gray whale is often touted as a poster child for successful conservation. In the 19th century, they were hunted to near extinction by eager whalers, but they were given a new lease of life in 1949, when the International Whaling Commission granted them protection from hunting. Today, the western Pacific population remains critically endangered, but the eastern Pacific whales have bounced back. On average, recent censuses put their numbers at about 22,000. Despite once skirting the brink of extinction, the eastern Pacific gray is now the most common whale in the western seaboard.
Cries of ‘full recovery’ were sounded, bolstered by the fact that several gray whales have recently been seen suffering from starvation. The assumption was that they had reached a population plateau, filling up the ecological niche that can support their large bulk. Even the American Cetacean Society claims that the whales are ‘probably close to their original population size.’But Alter argues that these celebrations are premature.
In 1979, somewhere in Dartmoor, a butterfly died. That would hardly have been an exceptional event, but this individual was a Large Blue butterfly (Maculinea arion) and it was the last of its kind in the United Kingdom. Over more than a century, the Large Blue’s population had been declining and it was finally declared nationally extinct 30 years ago.
Now, it’s back. A bold conservation effort managed to work out the factors behind the butterfly’s decline, and resurrect this vanished species. The Large Blue’s reintroduction has been one of conservation’s flagship successes and it was the first time that efforts to save a declining butterfly had actually paid off.
The victory hinged on strong science. Rather than relying on speculation and optimistic measures, a team of scientists led by Jeremy Thomas, David Simcox and Ralph Clarke carefully analysed the factors behind the butterfly’s decline to find the best ways of reversing it. Work started in 1974 and the butterfly staged its comeback in 1983. Now, on the 25th anniversary of its reintroduction, Thomas, Simcox and Clarke describe their efforts to bring the charismatic Large Blue back to England’s green and pleasant lands.
The Large Blue butterfly has a very strange lifestyle. When it hatches in July, its caterpillar feeds on thyme plants for three weeks and then drops to the ground to begin a more leisurely existence. The caterpillar so strongly mimics the smells and sounds of the ant Myrmica sabuleti that it is carried to the colony and cared for as if it were an actual ant. It spends the next 10 months of its life in this sheltered environment, and its mimicry ensures that its surrogate parents leave it alone, even when it eats their young.
Sixty-five million years ago, life on Earth was sorely tested. One or more catastrophic events including a massive asteroid strike and increased volcanic activity, created wildfires on a global scale and dust clouds that cut the planet’s surface off from the sun’s vital light. The majority of animal species went extinct including, most famously, the dinosaurs. The fate of the planet’s plants is less familiar, but 60% of those also perished. What separated the survivors from the deceased? How did some species cross this so-called “K/T boundary”?
Jeffrey Fawcett form the Flanders Institute for Biotechnology thinks that the answer lies in their genomes and specifically how many copies they have. Geneticists have found that the majority of plants have duplicated their entire portfolio of genetic material at some point in their evolution. They are called “polyploids” – species with multiple copies of the same genome.
By dating these doublings, Fawcett had found that the most recent of them cluster at a specific point in geological time – 65 million years ago, at the K/T boundary. It suggests that having extra copies of their genomes on hand gave these plants the edge they needed to cope with the dramatic environmental changes that wiped out the dinosaurs and other less well-endowed species.
The emperor penguin – caring parent, extreme survivor and unwitting movie-star – could be marching to extinction by the turn of the next century. In its Antarctic home, the penguins frequently have to deal with prolonged bouts of starvation, frosty temperatures of -40 degrees Celsius, and biting polar winds that blow at 90 miles per hour. And yet this icy environment that so brutally tests the penguins’ endurance is also critical to their survival. This is a species that depends on sea ice for breeding and feeding.
So what will happen to the emperor penguin as Antarctica’s sea ice shrinks, as it assuredly will in the face of a warming globe? Stephanie Jenouvrier from the Woods Hole Oceanographic Institution have tried to answer that question by combining the forty years of census data on a specific emperor colony with the latest models from the Intergovernmental Panel on Climate Change (IPCC).
The results are not encouraging. They suggest that the number of emperors in a large colony at Terre Adelie (where March of the Penguins was filmed) will fall from about 6,000 breeding pairs at the moment to a mere 400 by 2100. There’s even a one in three chance that the population will drop by 95%- a level described as “quasi-extinction”, when the population is so small that it’s unlikely to sustain itself.
Image copyright of Samuel Blanc