Tag: leaf

Pocket science – swordfish and flatfish are close kin, and ancient death-grip scars

By Ed Yong | August 17, 2010 7:00 pm

Marlin_turbot

Flatfish are the closest living relatives to swordfish and marlins

At first glance, a swordfish and a flounder couldn’t seem more different. One is a fast, streamlined hunter with a pointy nose, and the other is an oddly shaped bottom-dweller with one distorted eye on the opposite side of its face. Their bodies are worlds apart, but their genes tell a different story.

Alex Little from Queen’s University, Canada, has found that billfishes, like swordfish and marlin, are some of the closest living relatives to the flatfishes, like plaice, sole, flounder and halibut. This result was completely unexpected; Little was originally trying to clarify the relationship between billfishes and their supposed closest relatives – the tunas. That connection seems to make more sense. Both tunas and billfishes are among a handful of fish that are partially warm-blooded. They can heat specific body parts, such as eyes and swimming muscles, to continuously swim after their prey at extremely fast speeds with keen eyesight.

But it turns out that these similarities are superficial. Little sequenced DNA from three species of billfishes and three tunas, focusing on three parts of their main genome and nine parts of their mitochondrial one (a small accessory genome that all animal cells have). By comparing these sequences to those of other fish, Little found that the billfishes’ closest kin are the flatfish and jacks. Indeed, if you look past the most distinctive features like the long bills and bizarre eyes, the skeletons of these groups share features that tunas lack. Indeed, billfish and tuna proved to be only distant relatives. Their ability to heat themselves must have evolved independently and indeed, their bodies product and retain heat in quite different ways.

Little’s work is testament to the power of natural selection. Even closely related species, like marlins are flounders, can end up looking vastly different if they adapt to diverse lifestyles. And distantly related species like tuna and swordfish can end up looking incredibly similar because they’ve adapted to similar challenges – pursuing fast-swimming prey. This shouldn’t come as a surprise – a few months ago, a French team found that prehistoric predatory sea reptiles were probably also warm-blooded.

Reference: Molecular Phylogenetics and Evolution: http://dx.doi.org/10.1016/j.ympev.2010.04.022; images by Luc Viatour and NAOA

Ant_scars

Ancient death-grip scars caused by fungus-controlled ants

Forty-eight million years ago, some ants marched up to a leaf and gripped it tight in their jaws. It would be the last thing they would ever do. Their bodies had already been corrupted by a fungus that, over the next few days, fatally erupted from their heads. The fungus produced a long stalk tipped with spores, which eventually blew away, presumably to infect more ants. In time, all that was left of this grisly scene were the scars left by the ants’ death-grip. Today, David Hughes from Harvard University has found such scars in a fossilised leaf from Germany.

Today, hundreds of species of Cordyceps fungi infect a wide variety of insects, including ants. Like many parasites, they can manipulate the way their hosts behave. One species, Cordyceps unilateralis, changes the brains of its ant hosts so that they find and bite into leaves, some 25cm above the forest floor. The temperature and humidity in this zone are just right for the fungus to develop its spore capsules. In its dying act, the ant leaves a distinctive bite mark that’s always on one of the leaf’s veins on its underside. And that’s exactly what Hughes saw in his fossil leaf.

Hughes originally thought that the marks were made by an insect cutting the veins of the leaf to drain away any potential poisons, something that modern insects also do. But these marks look very different – those on the fossil leaf bear a much closer resemblance to those of Cordyceps-infected ants. This is the first fossil trace of a parasite manipulating its host, but it’s not the oldest evidence for such a relationship. In 2008, another American group found a 105-million-year-old piece of amber containing a scale insect, with two Cordyceps stalks sticking out of its head. The war between insects and their Cordyceps nemeses is an ancient one indeed.

Reference: Biology Letters http://dx.doi.org/10.1098/rsbl.2010.0521
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Culture shapes the tools that chimps use to get honey

By Ed Yong | October 23, 2009 8:05 am

There is a deep hole in a tree trunk and within is a tasty dollop of sweet, nutritious honey. It’s a worthwhile prize for any animal skilled or clever enough to reach it, and chimpanzees certainly have both of these qualities. But the solutions they find aren’t always the same – they depend on cultural traditions.

Chimps from the Sonso community in Uganda are skilled at the use of sticks and unsurprisingly, they manufacture stick-based tools to reach the honey. Chimps from the Kanyawara community in a different part of Uganda have never been seen to use sticks in the wild. Instead, they bring their considerable leaf-based technology to the fore, using leaves a sponges to soak up the hidden honey.

This is hardly the first time that chimps have demonstrated cultural traditions. Chimps in different parts of Africa have their own peculiar styles of tool technology and these variations are some of the strongest pieces of evidence for the existence of animal culture. Captive chimps can also transmit traditions between each other, once seeded by scientists.

But some sceptics are unconvinced. Their riposte is that genetic or environmental differences could equally have shaped technological differences. Alternatively, faced with abstract problems in captivity, chimps could learn solutions through trial-and-error, rather than picking up answers from their peers. To discount these possibilities, Thibaud Gruber from the University of St Andrews wanted to see if different groups of wild chimps would solve new problems in different ways, even though they shared similar genes and environments.

He found two groups of participants in the Sonso and Kanyawara communities of Uganda. Both live in forests and both are genetically similar enough that you couldn’t tell which group an individual chimp belonged to based on its genes. And both groups like honey.

When the chimps weren’t around, Gruber drilled holes in fallen logs, filled them with liquid honey, and dotted honeycombs around the rim to alert passing chimps. For such chimps, it would have been an unusual sight – they often rob beehives but the holes they pilfer are on vertical trunks, and the honey is solid, waxy and easily reachable.

If the hole was shallow, the chimps from both communities could use their hands to get the honey. For deeper prizes that could only be reached with tools, their strategies strongly differed – some of the Sonso chimps sponged the honey up with leaves, while almost all of the Kanyawara chimps dipped into it with sticks. No Sonso chimp used sticks and no Kanyawara chimp used leaves.

Gruber thinks that it’s extremely unlikely that the chimps were using a trial-and-error method to extract the honey, for they solved the problem both quickly and accurately. Despite having similar environments, genes and tasks, the two communities had their own specific approaches to the task. Their divergent cultures are reflected not just in the tools they used, but their

Kanyawara chimps try to eat honey about twice a month, and they succeed on around half of their attempts. In Sonso, honey is a much rarer part of the chimp diet. At both places, bees attack invading chimps with equal ferocity, but the Kanyawara group have become persistent and learned to regularly revisit the same spot. The Sonso group only eat honey when the opportunity presents itself. It’s no surprise then that the Kanyawara chimps spent longer in their quest for the hidden honey than their Sonso peers.

Reference: Current Biology DOI: 10.1016/j.cub.2009.08.060

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