‘Polka-dot’ termite mounds support thriving ecosystems

The regular polka-dot pattern of termite mounds on the savannah of central Kenya supports a great abundance of plant and animal life – more than the region could support without the termites. The discovery, made by American and Belgian scientists, suggests regular patterns like this are so beneficial we should expect to see them in many other ecosystems.

The red dots are termite mounds. Image: Robert M. Pringle/Plos Biology

While studying geckos on the African savannah, the scientists noticed that the lizards tended to congregate around the sprawling termite mounds. Looking more closely, they discovered that it wasn’t just lizards that preferred the mounds – they were covered in a dense layer of plants and animals. The numbers of plants and animals decreased as the scientists moved further away from the mound, suggesting the mounds were responsible for supporting a thriving local ecosystem, but how do they do so?

The scientists aren’t sure. They think the termites, which create elaborate nests up to ten metres across, alter the soil structure by mixing in larger particles of soil. This helps water filter down to plant roots. The termites also seem to stir into the soil more nutrients such as phosphates and nitrogen, which plants need to grow. Increasing the number of plants boosts herbivore and insect numbers, which draws in predators like the geckos.

It doesn’t stop there. The regular spacing of the termite mounds across vast swathes of savannah support a much more productive ecosystem on a much larger scale. The regular spacing means no area is very far from a mound and its life-supporting effects, so the entire ecosystem can be more productive.

The findings should also be useful in completely different environments: conservation work to restore coral reefs or forests can use the idea of regular ‘polka-dot’ spacing to ensure that the fragile ecosystems are as strong as possible while they recover.

Paper Reference: Pringle RM,  Doak DF,  Brody AK,  Jocqué R,  Palmer TM, (2010) Spatial Pattern Enhances Ecosystem Functioning in an African Savanna. PLoS Biology, 8(5). e1000377. doi:10.1371/journal.pbio.100037

Animals thrive without oxygen

We can’t survive for very long without oxygen. Researchers thought the same was true for every other animal, until an Italian and Danish team found tiny animals thriving in oxygen-free sediments deep below the Mediterranean Sea.

A Loricifera called Spinoloricus: tougher than it looks! Image: Danovaro et al (2010)/BMC Biology

The tiny animals are known as Loricifera, and they grow to just one millimetre long. They were found living in anoxic (or oxygen-free) sediment on the Mediterranean seafloor, in conditions that would kill other animals fairly quickly.

Anoxic basins in the Mediterranean seabed are some of the most extreme environments on Earth. Over 3000 metres below the waves, a thick layer of salty brine collects in shallow basins, preventing oxygen dissolved in the seawater from reaching the sediment. The sediment is also packed with poisonous hydrogen sulphides, and the water at that depth is under extreme pressure, meaning the Loriciferans need a whole host of specialist adaptations just to survive. They rely on a trick used by many extreme-living single-celled organisms to generate energy without using oxygen, but this is the first time anyone has seen a multi-cellular animal do so.

But how do researchers know that the Loriciferans were spending their entire lives in the anoxic basins? The tiny beasts may have just drifted in from another patch of seabed, died, and then been scooped up in the sediment samples. To make sure this wasn’t the case the researchers used a fluorescent dye that only stains living cells, showing many of the Loriciferans were still alive. They also showed that there was no way the creatures could just have drifted into the basin in which they were found.

Researchers have known for a long time that bacteria, viruses and other single-celled organisms can survive in such hostile conditions, but this is the first evidence that multi-cellular animals can live, and reproduce – the researchers found several Loriciferans carrying eggs – quite happily in this bizarre alien world.

Paper reference: Danovaro, R., Dell’Anno, A., Pusceddu, A., Gambi, C., Heiner, I. and Kristensen, R.M. (2010) The first metazoa living in permanently anoxic conditions. BMC Biology, 8:30 doi:10.1186/1741-7007-8-30

When less really could be more

Where do new species come from? Natural variability between the individuals in a population can gradually lead to the formation of a new species, particularly if a group becomes geographically isolated. But what happens if a population of animals loses some of that natural variability? It turns out that this too can lead to rapid evolution and the formation of new species.

A male from an all-orange population - unchallenged mating rights! Image: Ammon Corl/UC Santa Cruz

Male side-blotched lizards (Uta stansburiana) usually come in one of three colour ‘morphs’, which also correspond to their favoured mating strategy. Sometimes, however, one or two of the colour ‘morphs’ disappear from a population altogether: this leads to very quick evolutionary changes in the body size and other physical features of that population. Ultimately, these changes can lead to the population becoming an entirely new species.

The American researchers who conducted the study think this counter-intuitive result is down to the sudden change. Each of the three males is adapted to successfully compete with one of the others (leading to the biological equivalent of rock-paper-scissors) and when one is lost, the others have to re-adapt to the change in their surroundings – leading to a burst of evolutionary activity.

DNA analysis showed that the original population of side-blotched lizards contained all three colour morphs. Each morph is good at getting access to girls in one way: orange males are strong, and fight for and defend a large harem of females; blues are smaller and can only defend one female; yellows are sneaky – they look similar to females so can infiltrate the harem of an orange male, but cannot fool the blues. In some places the population switches between the three male strategies in turn, but in others the yellows, and sometimes blues, mysteriously disappear altogether.

The environment you live in consists of more than just the physical features of the landscape, or the predators and prey that share the local area. The influence of other members of your species can be an important evolutionary driving force – some scientists think it was the pressure of social living that led to the development of our large human brains. In the case of the side-blotched lizards, a change in their environment (the loss of a competitor for mates) leads to different selective pressures – and possibly even a whole new evolutionary path.

Paper Reference:    Corl, A., Davis, A.R., Kuchta, S.R., & Sinervo, B. (2010). Selective loss of polymorphic mating types is associated with rapid phenotypic evolution during morphic speciation. PNAS, published online before print February 16, 2010. doi:10.1073/pnas.0909480107

Are ice shelves destroyed by wave-power?

In 2008, several sections of the Wilkins Ice Shelf in Antarctica collapsed. Twelve hours earlier, storms along the South American coast generated a certain type of ocean wave with a very long period (the gap between the crest of one wave and the next). But are the two events, separated by thousands of miles, connected?

An Antractic iceberg - shaken free by waves? Image: NASA/Jane Peterson

Apparently so. American scientists have recently shown that these long period waves, called ‘infragravity’ waves, bend and flex floating ice sheets in the Antarctic much more than normal ocean swell. The collapse of the Wilkins Ice Shelf coincided with the arrival of infragravity waves: the great up-and-down movements of which probably created gaping crevasses and fractures in the Wilkins ice sheet, weakening it and ultimately leading to its collapse.

The scientists made the discovery by planting a seismometer – a device usually used to detect the movement of land during earthquakes – in a different patch of sea ice in Antarctica known as the Ross Ice Shelf. Ice sheets usually bob up and down with the motion of the waves underneath them, but the infragravity waves left a distinct signature of much larger movements in the data collected by the seismometer.

Although not the sole cause, infragravity waves could be the final trigger for collapse of already-weakened ice sheets. Melting water on the surface of the ice sheet probably also plays a part in ice sheet collapse but, as the scientists say, we are still a long way from understanding exactly what triggers the sudden collapse of thousands of square miles of ice into a flotilla of doomed wandering ice bergs.

Paper Reference: Bromirski, P., Sergienko, O., and MacAyeal, D. (2010) Transoceanic infragravity waves impacting Antarctic ice shelves. Geophysical Research Letters, 37, L02502. doi:10.1029/2009GL041488, 2010

Owls sing to the moon

Eagle owls use the moon to talk to one another at night, according to a European team of researchers. They found that Eurasian eagle owls (Bubo bubo) call more on moonlit nights, when the moonlight illuminates the white patch of feathers they expose only when calling out loud.

The  owls rely mostly on a vocal call to communicate, but drive home the message with a flash of white feathers. The owl’s call, together with the bright white feathers, makes them rather noticeable in the dark of the night.

Eagle Owls: wolves in owl's clothing? Image: Hypothesis Now

The owls also favour higher perches on moonlit nights, presumably taking advantage of the more exposed position to make the most of the light shining on their stark white feathers. In contrast, the owls were often silent on moonless nights and, if they did call, the owls tended to do so from a lower perch.

Many animals alter their behaviour depending on the phases of the moon. Usually, bright nights make it easier for predators to find prey, so small animals keep quiet when the moon is full. Eagle owls, however, have no natural predators so they’re free to make themselves as eye-catching as possible to ensure nearby owls get the message. They usually communicate most at dusk and dawn, but a full moon produces almost as much light and the owls have learned to take advantage of it to call long into the night.

It may sound obvious, but the point of signalling is to be understood, and animals have evolved lots of clever tricks to get their messages across: many other birds have repeating calls, so the message is repeatedly broadcast; Anole lizards bob their heads to make themselves stand out from the background; and poisonous insects often use bright contrasting colours to warn off prospective predators. The eagle owls have simply learned to take advantage of another source of light.

Paper reference: Penteriani, V.,  Delgado, M.d.M.,  Campioni, L.,  Lourenço, R. (2010) Moonlight Makes Owls More Chatty. PLoS ONE 5(1): e8696. doi:10.1371/journal.pone.0008696