Darwin and the Devil’s Garden

Science is strewn with controversial ideas and contradictory opinions. Eventually, one side or another in the debate is usually proved right, and science advances. Sometimes, very occasionally, it turns out both sides are right. The story of the ants and their tree-houses is one such occasion.

The Amazon Rainforest - here there be devils? Image: NASA

It starts, as so many evolutionary biology stories do, with a certain Charles Darwin. He observed that many ant species inhabit cosy little nodules, called domatia, on the branches of tropical trees. The ants kill any other insects that land on the tree, protecting the tree from harm. They also, in some cases, inject deadly formic acid into any other plants that take root in the area around their home tree, killing off any competitors before they can become established. This land-clearance leads to the formation of ‘devils’ gardens’ in tropical rainforests – area of forest where only one species of tree (called Duroia hirsuta), which houses the ants, can grow. In return for their diligent defence, the ants get safe lodgings in the tree’s specially-grown domatia. It’s a perfect example of ‘mutualism’, where both parties benefit from cooperation. At least, that’s how Darwin saw it.

Richard Spruce, a contemporary of Darwin, disagreed. He thought the ants were parasites, taking over trees and boring their own tunnels, which eventually produced the characteristic domatia as the tree responded to the damage the ants caused. The trees gained nothing from the relationship, and were powerless to stop the ants burrowing deep into their living tissue.

In the 1960’s, scientists showed that Darwin was right – the trees deliberately grow the nodules for the ants to inhabit, suggesting the relationship had mutual benefits for both tree and ant. Case closed, you may think. Well, not quite…

Recent research by a team of UK and American scientists has shown that some ants do in fact build their nests inside trees which do not grow welcoming domatia. The scientists were tipped off by local people, who found some unusual scars on nearby tree trunks. It turned out that the ants, known as Myrmelachista schumanni or lemon ants , build nests in domatia-free trees on the edge of the devil’s garden they have created, possibly as a result of overcrowding of their original tree-house homes.

So it turns out Spruce was also correct – the ants do parasitize some trees, digging out new homes in their trunks and branches, which has no benefit for the tree.

And the moral of our tale? Science is constantly changing, and there are few, if any, absolutes. For me, this is precisely what makes it so interesting: the constant search for knowledge of the natural world throws up many unexpected nuggets of information, and who knows what established ‘truth’ will be overturned next week?

Paper Reference: doi: 10.1086/606022

Mosquitoes threaten unique Galapagos wildlife

Disease-carrying mosquitoes are threatening the unique animal inhabitants of the Galapagos Islands, according to research carried out by the University of Leeds in the UK.

Galapagos species have evolved in isolation for so long that they’ve lost their immune defences, leaving them vulnerable to infections carried by the newly-arrived mosquitoes.

Researchers found mosquito stowaways on many of the recently-arrived tourist flights to the islands. Although the mosquitoes don’t arrive in great numbers they are able to survive and breed with native mosquitoes. It is this mingling of populations, brought about by the increasing Galapagos tourist trade, that could introduce new diseases to the Galapagos.

Tourism undoubtedly brings benefits to the human inhabitants of the Galapagos, but it also brings many risks. Rats arriving on cruise ships are eating their way through the eggs of native birds, including ground-nesting Galapagos penguins; introduced pigs destroy turtle and iguana nests; and goats chomp their way through much of the specialised native plant-life. Now regular introduction of mosquitoes threatens to bring new diseases to blight the islands.

The animals that inhabit the Galapagos Islands in the South Pacific have evolved into unique forms during their long isolation from the mainland: nowhere else on the planet can you find the bizarre marine iguanas or the varied Galapagos mockingbirds that inspired Darwin! Unfortunately, the isolated conditions also led to the animal’s greatest weakness – their vulnerability to introduced diseases and predators.

The Galapagos Islands have a special place in the history of science as one of the places that helped Charles Darwin to develop the theory of evolution. It would be a tragic loss if the unique animals the islands harbour were destroyed through our carelessness. Sadly, it may only be a matter of time.

Marine iguanas: probably the weirdest lizards on Earth...

Image credit: flickr/putneymark. Used under this license

On The Origin of Flowers

This beetle recognises the importance of flowers. Do you?

Flowers are incredibly important. Flowering plants feed us, clothe us, and provide many of our medicines. In fact, flowering plants arguably form the basis for all human society, but how did they become so widespread and successful?

New research by two Dutch scientists has given us an insight into how this group of plants managed to spread around the world. Incredibly, it’s because they share one particular trait with humanity – they are able to alter their environment to suit their own needs.

Flowering plants are better able to make use of nutrients in the soil, specifically nitrogen. The leaves and petals they drop also decay faster than the tough leaves of non-flowering plants such as conifers. This means that flowering plants can out-compete non-flowering plants for nutrients, while at the same time quickly replenishing the nutrients available – further enhancing their own survival chances.

The fossil record shows that flowering plants first appeared 125 million years ago, in the early Cretaceous period – famous as the last period in Earth’s history dominated by the dinosaurs. By the end of the Cretaceous period, around 65 million years ago, the flowering plants had taken over as the dominant plant-life all around the world.

Charles Darwin was confounded by flowers. He couldn’t explain how they spread so quickly from isolated, marginal environments mostly ignored by other plants, to global dominance. He went so far as to describe them as an “abominable mystery”! This research provides a plausible answer to part of that mystery.

Unfortunately, we still don’t know how flowering plants became established in the first place: the rise of insect pollinators, changing atmospheric levels of CO₂, or more small dinosaurs have all been suggested as potential mechanisms. Either way, once the flowering plants were established it seems as though their dominance was assured. From a human perspective, this was a very good thing!