dimanche 30 mars 2014


From beetles mating with bottles to frogs swallowing light bulbs, creatures are struggling to keep up with the changes humans make, says Christopher Kemp

ON THE Caribbean island of St Kitts, a colony of exuberant vervet monkeys patrols the beach, waiting to pounce on unattended drinks. When they spot one, they scamper acrobatically across the sand to steal it. They fight. They drink. They overturn tables. Finally, as the sun slides over the horizon, they slump clumsily onto the sand. Scientists have been studying the drunken monkeys of St Kitts for decades, using them to research the neural pathways involved in alcoholism. But they represent more than just a primate model of addiction. According to biologist Bruce Robertson at Bard College in New York, the monkeys are caught in an “evolutionary trap”. Their enjoyment of alcohol exists for a very good reason, he says: they evolved to crave energyrich foods. But now that piña coladas are easier to obtain than bananas, it has become a liability. “It’s an incorrect behaviour that happened because we changed the environment too fast for evolution to catch up,” Robertson says. Evolutionary traps – also called ecological traps – are everywhere. They have been found in almost every type of habitat, affecting mammals, birds, reptiles, amphibians, fish and insects. Bamboozled by rapid environmental change, these animals can no longer accurately assess the suitability  of food resources, mates, habitats or much  of anything else. Bad choices look like good ones, and the animals are lured into an evolutionary dead-end. In this new world, a male giant jewel beetle lands on a beer bottle and tries to mate with it. The reflective qualities of the amber-coloured glass have fooled it into believing the bottle is a female giant jewel beetle (see below).  A Cuban tree frog swallows a fairy light in a backyard in Florida, responding as if the bulb were a tasty insect. Our opening photograph shows that frog, lit from within, dangling like a bizarre Christmas ornament (see page 43). Futile embrace At sea, albatrosses and turtles mistake small pieces of colourful plastic for food and die,  full but starved. Newly hatched turtles mistake the lights of beachside hotels for the horizon and crawl away from the sea towards bustling resorts where they perish. Male California redlegged frogs mistake juveniles of an invasive frog species for females of their own species, clasping them for hours in a futile embrace. The list goes on; the effects are catastrophic. In a recent analysis, Robertson identified 40 types of evolutionary trap, some of  which affect hundreds of species. Traps can  be created by all kinds of human activity, including agriculture, ecological restoration, ALAMYCELEBRITY/ALAMY “ There is no faster way  to crash a population than an evolutionary trap” buildings and pollution. The worst trap is the introduction of invasive species (Trends in Ecology & Evolution, vol 28, p 552). Even when humans try to perform good deeds we can inadvertently set evolutionary traps. In Israel, in an effort to protect a population of endangered salamanders, conservationists began planting trees, gradually turning a desert into a wetland. “No trees previously existed,” says Robertson. “They put them in to help the revegetation project. And that attracted a bird – a predatory bird.” Almost overnight, the forest provided perches for hungry southern grey shrikes, turning a salamander-friendly habitat into  a death trap. You can guess what happened  to the salamanders. The concept of an evolutionary trap  was first put forward in the early 1970s but  did not attract as much attention as other effects of environmental change. In a survey published in 2006, Robertson failed to find many published examples, concluding that the traps are either rare, difficult to detect,  or both (Ecology, vol 87, p 1075). So he set out to develop tools to identify them. “I was interested in the topic but there were no criteria by which a scientist could say, ‘I have found A, B and C; therefore I have found an evolutionary trap’,” he says. That has changed. “Now we have some basic tools to say, here’s how we find them,” says Robertson The one-sentence version would be: Do you prefer the thing that’s worse for you? The slightly more accurate version would be: the cues you use to make your decisions no longer lead you to the best decisions – in fact they lead you to make the worst ones.” Having worked out how to identify traps, ecologists are slowly beginning to understand how they exacerbate human impacts on fragile and changing ecosystems. “There’s no faster way to crash a population than if it is caught in an evolutionary trap,” says Robertson. For instance, if deforestation removes half of a rainforest, you would expect half the animals to be lost. But many species of mammal, bird and insect are attracted to “edge habitats” on the fringes of forests. Others find food resources plentiful in areas of freshly cut woodland. But these habitats are traps: they may offer gains in terms of food but they also expose animals to predators and other risks, such as roadways. If the remaining species migrate and relocate to around the deforested areas, many more than half will vanish. One of the worst traps affects aquatic insects such as caddis flies and mayflies. For many insect species, one of the most important decisions is where to lay their eggs. In the case of aquatic insects, this means water.“When light bounces off water, it gets polarised,” says Robertson. “This polarised light was so uniquely associated with water that many types of organism evolved eyes that can see it.” That’s how aquatic insects detect suitable egg-laying habitats. But there’s a problem. Modern landscapes now teem with artificial surfaces that polarise light in exactly the same way that water does. “Aquatic insects lay their eggs on buildings and solar panels and asphalt and cars, thinking that they’re laying on water,” says Robertson. “They actually prefer to lay their eggs on automobiles than on a nearby lake, even if they can see the lake.” The billions of insect eggs laid on these objects will never hatch. People traps Just like the vervet monkeys and aquatic insects, humans have also become entangled in evolutionary traps of our own making, says Robertson. “Probably the most likely evolutionary trap for humans, or at least the most discussed, would be fast food,” he says. But there are many others: pornography, gambling, video gaming, drugs. All of these hijack behaviours that evolved to aid survival. In principle, some traps can be easily fixed. “The things that polarise light are smooth and black,” says Robertson, “so if you have a building that caddis flies are laying their eggs on, you can put up white curtains. You can build your building out of something lighter. If you have an asphalt road that’s attracting dragonflies to lay their eggs, add a little more gravel to it so it’s less smooth. Don’t put solar panels near wetlands. There are all kinds of really simple fixes.” Sometimes, though, you don’t want to  fix a trap. Robertson thinks it’s possible to  set traps on purpose. He calls these virtuous evolutionary traps. Every year, in countries across the developing world, hundreds of millions of people are infected with malaria by mosquitoes carrying parasitic protozoans. The World Health Organization estimates there were  207 million cases of malaria worldwide in 2012, which caused about 627,000 deaths. Could a carefully constructed evolutionary trap change that statistic, drastically reducing the number of new infections? Is it possible  to funnel the mosquitoes away from people  at risk of contracting the disease? If billions of mayflies can be fooled into laying their eggs on cars, buildings and solar panels, perhaps mosquitoes can be fooled too. “I think it is a fantastic idea and one that I’ve specifically considered, though the exact way you would do it would be tricky,” says Robertson. Ken Pienta is thinking along the same lines, but on an even smaller scale. An oncologist at Johns Hopkins University School of Medicine in Baltimore, Maryland, Pienta wants to set a trap to catch metastasising cancer cells. “My laboratory is trying to understand cancer as an ecosystem, and how we can develop what we’ve termed eco-therapies,” he says. In other words, an ecosystem isn’t just something like a wetland – it could be a person with metastatic cancer, too. Just as California red-legged frogs in the wetland can be fooled into attempting to mate with the wrong species of frog, could cancer cells be lured into similarly fruitless behaviour? Pienta thinks so. In the future, he says, doctors could insert a device filled with a chemokine – a protein that attracts cancer cells – into a person with cancer to prevent a tumour from metastasising to other tissues. Or perhaps oncologists will convince cells to metastasise to a part of the body from which it can easily be removed. “Some of it sounds a little bit like science fiction, but there are many people working on chambers that can be inserted into a vein,” Pienta says. “You could design a one-way  filter to sit in the bloodstream and just attract circulating tumour cells, and then just take them out of that trap every couple of days.” For Robertson, the hard work has just  begun. “Think about this,” he says. “We have all kinds of invasive species, all kinds of problematic species that need to have their numbers reduced. Nothing might work  better than creating evolutionary traps to control or eradicate pest species.” “You could take a catastrophe,” Robertson says, “and turn it into a tool.”  ■

Aucun commentaire:

Enregistrer un commentaire

Copyright © 2013 Key Pirate
Distributed By Free Blogger Templates | Design by FBTemplates | emThemes
    Twitter Facebook Google Plus Vimeo Videosmall Flickr YouTube