This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science.
Attention-deficit hyperactivity disorder is the most common developmental disorder in children, affecting anywhere between 3-5% of the world’s school-going population. As the name suggests, kids with ADHD are hyperactive and easily distracted; they are also forgetful and find it difficult to control their own impulses.
While some evidence has suggested that ADHD brains develop in fundamentally different ways to typical ones, other results have argued that they are just the result of a delay in the normal timetable for development.
Now, Philip Shaw, Judith Rapaport and others from the National Institute of Mental Health have found new evidence to support the second theory. When some parts of the brain stick to their normal timetable for development, while others lag behind, ADHD is the result.
The idea isn’t new; earlier studies have found that children with ADHD have similar brain activity to slightly younger children without the condition. Rapaport’s own group had previously found that the brain’s four lobes developed in very much the same way, regardless of whether children had ADHD or not.
But looking at the size of entire lobes is a blunt measure that, at best, provides a rough overview. To get an sharper picture, they used magnetic resonance imaging to measure the brains of 447 children of different ages, often at more than one point in time.
At over 40,000 parts of the brain, they noted the thickness of the child’s cerebral cortex, the brain’s outer layer, where its most complex functions like memory, language and consciousness are thought to lie. Half of the children had ADHD and using these measurements, Shaw could work out how their cortex differed from typical children as they grew up.
Ah, penguins. You just can’t help but smile. These animals are found on Boulders Beach near Cape Town, where they come so close to the erected walkways that you could potentially reach out and grab one (if the mood took you and you were an idiot).
The African penguin (Spheniscus demersus) is part of a genus with four species. The last time I saw one of them, it was off the Galapagos Islands (the Galapagos penguin), and the other two members of the group (the Humboldt and Magellanic penguins) are natives of Patagonia. They’re commonly known as jackass penguins because of their distinct, braying calls.
If you’re wondering why they look so huddled, it’s because the beach was being sandblasted by ridiculously strong winds, as if often the case near Cape Town. We only really managed to get a few photos as a time before having to retreat and gently wipe sand off the lens.
The hammerhead shark’s head is one of the strangest in the animal world. The flattened hammer, known as a ‘cephalofoil’, looks plain bizarre on the face of an otherwise streamlined fish, and its purpose is still the subject of debate. Is it an organic metal detector that allows the shark to sweep large swathes of ocean floor with its electricity-detecting ability? Is it a spoiler that provides the shark with extra lift as it swims? All of these
theories hypotheses might be true , but Michelle McComb from Florida Atlantic University has confirmed at least one other -the hammer gives the shark excellent binocular vision.
Depending on who you believe, there are anywhere from 8-10 species of hammerheads, whose cephalofoils all have different degrees of exaggeration. The bonnethead (Sphyrna tiburo) has a shape that’s more spade than hammer. The scalloped hammerhead (Sphyrna lewini) has a more familiar racing-car-spoiler shape. And the winghead shark (Eusphyra blochii) has the most elongated head of all, up to 50% of its entire body length.
She compared all of these flattened visages with those of two more typical sharks – the lemon and the blacknose. McComb collected her hammerheads by fishing for them off the coast of Hawaii and Florida and housed them in local tanks. She tested their eyes by sweeping arcs of light across them and measuring their responses using electrodes.
She found that hammerhead eyes, though far apart, have the greatest overlap in their fields of view. The winghead shark has a 48 degree arc in front of it that’s covered by both eyes, which must give it exceptional depth perception. By comparison, the scalloped hammerhead has a binocular overlap of 34 degrees, the bonnethead has a much smaller one of 13 degrees, and the lemon and blacknose sharks have the smallest of al with 10 and 11 degrees respectively.
And that’s if the sharks swim straight ahead with their heads completely still. A hammerhead can improve its stereoscopic vision even further by rotating its eyes and sweeping its head from side to side. McComb measured these movements too by filming the sharks swimming around their tanks.
Taking these movements into account, she found that the binocular overlaps of the scalloped hammerhead and bonnethead increase to a substantial 69 and 52 degrees respectively, still outclassing the 44 and 48 degree arcs of the pointy-headed species. The hammerhead species even have visual fields that overlap behind them, giving them a full 360 degree view of the world.
You might think that these visual fields would only overlap some distance ahead of the hammerheads, but not so – their eyes are angled slightly forwards so that ahead of them, their blind spots are just as small as those of sharks with narrower eye-spans. Their main weaknesses are substantial blind spots above and below their heads. Indeed, McComb says that there are some anecdotal reports of small fish giving them the slip by swimming into these regions above and below the hammer.
McComb’s results settle a long-standing debate. In 1942, some scientists have suggested that the hammerhead’s eyes are so far apart that their visual fields couldn’t possibly overlap. Others have argued that the wide spacing actually improves their binocular vision. Despite over 50 years of argument, this is the first study to actually do some measurements with real sharks, and it shows that their binocular vision is indeed improved by their odd heads.
Reference: Journal of Experimental Biology doi:10.1242/jeb.032615
More on sharks:
I have now written 600 posts for this blog (give or take a few – I think the “hearing with skin” story was 601).
The next lot of 100 posts will start tomorrow but for the moment, a brief interlude and over to you. Say whatever you’d like – about this blog, about science, about journalism, about wildlife, whatever really.
What part of the body do you listen with? The ear is the obvious answer, but it’s only part of the story – your skin is also involved. When we listen to someone else speaking, our brain combines the sounds that our ears pick up with the sight of the speaker’s lips and face, and subtle changes in air movements over our skin. Only by melding our senses of hearing, vision and touch do we get a full impression of what we’re listening to.
When we speak, many of the sounds we make (such as the English “p” or “t”) involve small puffs of air. These are known as “aspirations”. We can’t hear them, but they can greatly affect the sounds we perceive. For example, syllables like “ba” and “da” are simply versions of “pa” and “ta” without the aspirated puffs.
If you looked at the airflow produced by a puff, you’d see a distinctive pattern – a burst of high pressure at the start, followed by a short round of turbulence. This pressure signature is readily detected by our skin, and it can be easily faked by clever researchers like Bryan Gick and Donald Derrick from the University of British Columbia.
Gick and Derrick used an air compressor to blow small puffs of air, like those made during aspirated speech, onto the skin of blindfolded volunteers. At the same time, they heard recordings of different syllables – either “pa”, “ba”, “ta” or “da” – all of which had been standardised so they lasted the same time, were equally loud, and had the same frequency.
Gick and Derrick found that the fake puffs of air could fool the volunteers into “hearing” a different syllable to the one that was actually played. They were more likely to mishear “ba” as “pa”, and to think that a “da” was a “ta”. They were also more likely to correctly identify “pa” and “ta” sounds when they were paired with the inaudible puffs.
This deceptively simple experiment shows that our brain considers the tactile information picked up from our skin when it deciphers the sounds we’re listening to. Even parts of our body that are relatively insensitive to touch can provide valuable clues. Gick and Derrick found that their fake air puffs worked if they were blown onto the sensitive skin on the back of the hand, which often pick up air currents that we ourselves create when we speak. But the trick also worked on the back of the neck, which is much less sensitive and unaffected by our own spoken breaths.
While many studies have shown that we hear speech more accurately when it’s paired with visual info from a speaker’s face, this study clearly shows that touch is important too. In some ways, the integration of hearing and touch isn’t surprising – both senses involve detecting the movement of molecules vibrating in the world around us. Gick and Derrick suggest that their result might prove useful in designing aids for people who are hard of hearing.
Reference: Nature doi:10.1038/nature08572
More on perception:
The role of Velociraptor’s infamous claw has received much attention from scientists ever since they clicked their way across a movie kitchen. In comparison, the formidable claws of living raptors (birds of prey) have received little attention. Eagles, hawks, falcons and owls are some of the most widespread and well-liked of all birds. They are superb hunters and even though it’s always been suspected that they use their talons to kill, we know amazingly little about their techniques.
Denver Fowler (great name for an ornithologist) and colleagues from Montana State University have changed all of that, through the first comprehensive study of raptor feet. Their work reveals that these apparently familiar birds use a striking variety of killing strategies including some rather grisly ones. Some raptors use their talons to attack with high-speed killing blows, and others suffocate their prey to death in constricting fists. Some give their victims a merciful death by broken neck, but others eat their victims alive after slashing them open.
Fowler unveiled this macabre and violent world by measuring and photographing the talons and feet of over 34 birds from 24 raptor species. He also considered over 170 video sequences of raptor attacks, as well as many published accounts of predatory behaviour. By linking shape and size to actual behaviour, he managed to document the wide range o uses that curved claws can be put to.
Fowler found that raptors use their talons in a similar way when tackling small prey. Their feet are used to imprison their prey, with talons deployed as a cage rather than as weapons. Falcons use a notched ridge on their upper beak – the ‘tomial tooth’ – to sever the spine or crush the head, while owls sometimes break their prey’s neck with a swift twist. Accipitrids (eagles, hawks, kites, harriers and the like) have weaker bites than falcons and no ‘teeth’ – they use their feet to constrict their prey, cutting off its air supply much like a python uses its coils.
Owls tend to ambush their prey on the ground and their chances of landing a killing blow are slimmer. So they have evolved feet that are better at restraining struggling prey. Their toes are shorter and stronger than those of other raptors, and one of them can swivel backwards so that the owl can grip with two pairs of opposing toes. That makes them powerful constrictors, capable of crushing small animals in a suffocating ‘fist’. It also means that they specialise on smaller victims, and rarely tackle the larger prey that falcons and eagles do.
Larger prey simply can’t be enclosed by feet, so falcons and accipitrids use different strategies when their meals get bigger. They’ll stand on top of the animal, pinning it down with its full body weight. If the prey tires and stops moving, it’s all over, but death only comes after a “prolonged and bloody scenario”. The raptor plucks any fur or feathers, especially around the belly, and starts to feed, often using the large second claw to slash open the body and expose the innards. Grimly, the prey is sometimes still alive when this happens – it’s only the ensuing blood loss or organ failure that finishes them.
Accipitrids are more likely to consume their victims alive, and to subdue any final struggles, they have two unusually massive talons on the first and second toes that provide extra grip. These piercing anchors give them the ability to cope with the most powerful of struggling prey, and it’s no coincidence that the accipitrids include the mightiest of the raptors.
Falcons, on the other hand, often kill their prey with a neck-break to avoid a protracted struggle, so they can afford to have smaller talons. Their prey is also more likely to be seriously injured already. Falcons specialise in high-speed assaults, striking their prey with rapid dives and swoops that can potentially cripple them or even kill them outright.
Aside from size, the type of prey doesn’t have much of an impact on the shape and proportions of the raptor foot. The only exceptions are those species that are specialist fishermen, such as the osprey, the bald eagle and the fishing owl. Their talons are like fishhooks – exceptionally large, highly curved and equal in size on all the four toes.
Considering how popular and common the birds of prey are, it’s amazing that a study like this has never been attempted before. Even now, Fowler sees it as just the beginning. There’s no reason why the same sort of analysis shouldn’t apply to meat-eating dinosaurs, the extinct relatives of today’s raptors, and that will form the plot of his sequel study.
Reference: Fowler, D., Freedman, E., & Scannella, J. (2009). Predatory Functional Morphology in Raptors: Interdigital Variation in Talon Size Is Related to Prey Restraint and Immobilisation Technique PLoS ONE, 4 (11) DOI: 10.1371/journal.pone.0007999
More on birds of prey:
For the pipefish (and their relatives, seahorses and sea dragons), it’s the males who get pregnant. After a male fertilises the female’s eggs, he takes them up into a special brood pouch and shelters them until the babies hatch from his pot-bellied stomach several weeks later. He may seem like a shoe-in for the Dad-of-the-year award but this fatherly commitment has a sinister side to it. Not all of the babies he cares for make it out of his stomach alive.
Gry Sagebakken from the University of Gothenburg has proved that pregnant male pipefishes absorb some of the eggs and embryos within their pouches. By secretly cannibalising a proportion of his brood, he gets an extra boost of nutrients. The young he carries around aren’t just his next of kin, they’re also ready-made snacks.
Previously, Ingrid Ahnesjo showed that male pipefish ‘give birth’ to fewer youngsters than expected. During his pregnancy, some embryos were clearly lost. To track the fate of these lost eggs, Ahnesjo and Sagebakken injected females with a mixture of mildly radioactive amino acids. These were incorporated into newly created proteins, including those within the female’s eggs. Males were allowed to mate with both normal and irradiated females, so that half of the eggs in their bellies were radioactive and half were not.
They found that some of the radioactivity ended up in the male’s own tissues, including his liver and his muscles. This was the answer to the mystery of the missing embryos – daddy absorbs them into their own flesh. The fact that his brood pouch is lined with tangled networks of blood vessels makes it easier to do this.
Others have suggested that the lost embryos are actually “nurse eggs”, laid specifically to feed their siblings and act as their first meal. But not according to Sagebakken’s experiments, which show no traces of radioactivite amino acids in the eggs that didn’t contain them in the first place. The babies weren’t absorbing their potential siblings.
Either way, this is a prime example of the sorts of conflicts that can arise between animal parents and their offspring. Humans may romanticise the role of fathers and mothers, but studies like this show that for many animals, their interests of parents and children are often not aligned.
Should a parent ensure their offspring’s survival at the cost of their own health, or their chance to raise another generation? Should a youngster make demands on its parents for its short-term gain at the expense of a lower quality of care in the future? It’s a fine balancing act, and one that leads many animal parents to thin the size of their broods, killing or even eating them.
These trade-offs depend on many things like the size of each generation, the quality of one’s partners, the number of babies, the health of the parents, and so on. Sagebakken’s next step is to see if the males cannibalise more of their brood if they’re hungrier, and if the survivors actually benefit from their siblings’ demise. She also wants to understand if the male pipefish actually kills some of his offspring or just recycles the nutrients from embryos that are already dead or dying.
Reference: Proceedings of the Royal Society B doi:10.1098/rspb.2009.1767
Image: from Wikipedia by Tewy
More on animal parents:
Many thanks to the kind folks at PCMag for including me on their list of Top 50 blogs of 2009. However, they appear to have made a teensy little typo, where they’ve misspelled my name as “Patrick Jordan”. Easy enough a mistake, I guess – at least the letters D, O and N are shared…