As Charles Darwin learned several centuries ago, islands are havens for evolution. Newcomers to these isolated worlds find themselves unshackled from the predators that dogged them on the mainland. They celebrate their freedom by diversifying into a great variety of species. But predators still have ways of tracking them down, and following the footsteps of sailors is one of them. By killing adults and eating eggs, introduced predators such as rats, cats and stoats are responsible for nine in ten of the bird extinctions since 1600.
Now, conservation agencies are getting serious about introduced predators. As an example, they have spent increasingly large budgets in recent years on the eradication of rats from troubled islands. Smaller stowaways like mice typically escape the conservationists’ wrath, and between 2001 and 2005, twenty-five times less money was spent on dealing with them. After all, mice are smaller and less opportunistic than rats and pose very little threat to seabirds.
Or at least that was what scientists used to think. In 2005, Ross Wanless, Peter Ryan and colleagues from the University of Cape Town found that on Gough Island in the south Atlantic, mice had developed sinister appetites. They were eating the chicks of local seabirds alive (see image below).
For some reason, I’ve only just discovered the navel-gazing blogger meme that started at Nature Network a few weeks ago. But I’ve written up a shed-load of science this week and I’m feeling lazy and introspective. So better late than never…
It goes without saying that we are capable of noticing changes to our bodies, but it’s perhaps less obvious that the way we perceive our bodies can affect them physically. The two-way nature of this link, between physicality and perception, has been dramatically demonstrated by a new study of people with chronic hand pain. Lorimer Moseley at the University of Oxford found that he could control the severity of pain and swelling in an aching hand by making it seem larger or smaller.
Moseley recruited 10 patients with chronic pain in one of their arms and asked them to perform a series of ten hand movements at a set intensity and to a set pace. The volunteers had to watch their arms as they went through the motions. On some trials, they did so unaided, but on others, they viewed their arms through a pair of binoculars that doubled their size, a pair of clear-glass binoculars that did not magnify at all, or a pair of inverted binoculars that shrunk the image.
On each trial, Moseley asked the recruits to rate their pain on a visual sliding scale. He found that they were in greater pain after they had moved their arms – no surprise there. But the amount of pain they felt depended on how large their arm appeared to them. They experienced the greatest degree of extra pain when they saw magnified views of their arms, and took the longest amount of time to return to normal. Perhaps more surprisingly, the “minified” images actually evoked less pain than normal.
Clad in hard, armoured shells, turtles have a unique body plan unlike that of any other animal. Their shells have clearly served them well and the basic structure has gone largely unchanged since the time of the dinosaurs. But this unchanging nature poses a problem for anyone trying to understand how they evolved and until now, fossil turtles haven’t provided any clues. All of them, just like their living descendants, have fully formed two-part shells.
But three stunning new fossils are very different. They belong to the oldest turtle ever discovered, which lived about 220 million years ago in the area that would become China. Unlike today’s species, its mouth had a full complement of small, peg-like teeth but even more amazingly, it had a feature that distinguishes it from any other turtle, either living or extinct – it only had half a shell.
The ancient turtle was unearthed by Chun Li (no, not that one) from the Chinese Academy of Sciences, who called it Odontochelys semitestacea, a name that literally means “toothed turtle in a half-shell”. It was a small animal, just 35 cm from snout to tail, and its shell consisted of just a plastron (the bottom half) and not a carapace (the top half).
Li’s team believes that this incomplete shell represents an intermediate step along the evolutionary path to the modern version. To them, Odontochelys‘s anatomy settles debates about how the group’s distinctive shell evolved, which animals they were most closely related to and what sort of lifestyles the earliest members had. It’s a true hero in a half-shell.
Animal fossils are usually the remains of hard structures – bones and shells that have been petrified through enormous pressures acting over millions of years. But not all of them had such hard beginnings. Some Chinese fossils were once the embryos of animals that lived in the early Cambrian period, some 550 million years ago. Despite having the consistency and strength of jelly, the embryos have been exceptionally well preserved and the structure of their individual cells, and even the compartments within them, have been conserved in all their beautiful, minute detail.
They are a boon to biologists. Ever since the work of Ernst Haeckel in the 19th century, comparing the development of animal embryos has been an important part of evolutionary biology. Usually, scientists have to piece together the development of ancient animals by comparing their living descendants. But the preserved embryos give the field of embryology its very own fossil record, allowing scientists to peer back in time at the earliest days of some of the earliest living things. But how did these delicate structures survive the pressures of the ages?
Elizabeth Raff from Indiana University has a plausible answer. Her experiments suggest that fossil embryos are the work of colonies of ancient bacteria, which grew over the dead clumps of cells and eventually replaced their organic matter with minerals. They are mere casts of the original embryos.
Have you ever seen someone that you’re sure you recognise but whose face you just can’t seem to place? It’s a common enough occurrence, but for some people, problems with recognising faces are a part of their daily lives. They have a condition called prosopagnosia, or face blindness, which makes them incredibly bad at recognising faces, despite their normal eyesight, memory, intelligence, and ability to recognise other objects.
Prosopagnosia can be caused by accidents that damage parts of the brain like the fusiform gyrus – the core part of a broad network of regions involved in processing images of faces. That seems straightforward enough, but some people are born with the condition and their background is very different. They lack any obvious brain damage and indeed, brain-scanning studies have found that the core face-processing areas of their brains are of normal size and show normal activity.
But these studies were looking in the wrong place – the core regions aren’t the problem, it’s the connections between them that are faulty. Different parts of the brain are connected by tracts of ‘white matter‘ – bundles of nerve cell stalks that transmit messages between distant regions. They are the equivalent of cables that link a network of computers together and in people born with prosopagnosia, these neural cables are shredded or missing, even though the individual machines work just fine.
Over the past decade, some coastal waters have started turning red with alarming frequency. The cause is not some Biblical plague, but dense concentrations of microscopic algae called dinoflagellates. Red tides can often contain more than a million of these cells in a mere millilitre of water. Many are harmless and essential parts of the ocean environment, but others produce toxins that can kill local wildlife and risk the health of humans who eat their poisoned flesh.
These “harmful algal blooms” are more common in warm waters that mix poorly and are unusually rich in nutrients. Their increasing frequency has been blamed on numerous causes, from natural causes, to agricultural run-offs to increasing sea temperatures caused by climate change. But, as is becoming increasingly apparent in ecology, you’re not getting a complete picture of a habitat if you don’t know find out what the local parasites are up to.
Aurelie Chambouvet from the Station Biologique found that the algae responsible for red tides are themselves the victims of other parasitic species of dinoflagellates called Amoebophrya. The parasites act as an natural alga-stat that keeps the local algae populations under a tight leash. The red tides are what happens when that leash breaks.
Chambouvet’s team discovered the abundance of these parasites by taking water samples from an estuary of the Penze River in northern France over three consecutive years,. They used multi-coloured glowing antibodies designed to recognise and stick to molecules unique to both the host species and their parasites. The fluorescent glows revealed a life cycle that, like those of most parasites, is full of brutality and exploitation.