Aphids' dangerous liaison - October 10, 2007 / http://blogs.nature.com/news/thegreatbeyond/2007/10/aphids_dangerous_liaison.html

Par Jean-Luc Goudet - Futura-Sciences

Comment des organismes vivant dans l'eau peuvent-ils se retrouver dans des gouttes d'ambre, c'est-à-dire de la résine fossilisée, extrêmement hydrophobe ? La réponse n'était pas claire, d'autant que le cas est exceptionnel. Mais des chercheurs sont tombés sur une collection complète dans un lac de Floride, avec des inclusions de bactéries aquatiques. De quoi espérer bien d'autres découvertes...

http://www.futura-sciences.com/fr/sinformer/actualites/news/t/paleontologie/d/piege-dambre-pour-animaux-aquatiques_13131-1/

Par Jean-Luc Goudet - Futura-Sciences

Selon une étude américaine, l'insecticide produit par le maïs génétiquement modifié Bt, abondamment utilisé aux Etats-Unis, agirait aussi sur les insectes des cours d'eau, notamment via le pollen.

http://www.futura-sciences.com/fr/sinformer/actualites/news/t/developpement-durable-1/d/ogm-le-mais-transgenique-bt-affecterait-la-faune-aquatique_13148/

26 July 2007; | doi:10.1038/news070723-9 / http://www.nature.com/news/2007/070723/full/070723-9.html

Sex change wipes out invasive species

'Trojan chromosomes' enlisted in battle against alien invaders.

Louis Buckley

Altering their chromosomes could help deal with fishy pests. NOAA

Gender-bending chemicals could provide a new way to combat invasive species, say researchers. Originally conceived as a cure for the enormous populations of Asian carp and tilapia plaguing the Mississippi River, scientists now think the approach could be used to battle unwelcome crustaceans, molluscs, fish, amphibians and reptiles around the world.

Invasions of exotic species are thought to be second only to habitat destruction as a threat to global biodiversity. The traditional approach to dealing with these interlopers has been to introduce a known predator and let nature take its course. But this has led to numerous disasters - for example, cane toads swamped Australia after being introduced to control the cane beetles blighting the country's sugar crop.

In Florida, tilapia were deliberately introduced to control an aquatic weed, Hydrilla, that has been choking US rivers since the 1960s. Two species of snail were also introduced at a later date by the authorities, says Gutierrez, but neither they nor the tilapia chose to feed on Hydrilla, both preferring native species to the invader.

Hormone-determined gender

In 2004, alerted to Florida's problems with invasive species, Juan Gutierrez, a bio-mathematician at Florida State University, constructed a mathematical model of a population in which males carry two different sex chromosomes (XY) and females are XX. In many species of fish, amphibians, and other animals, gender is determined not only by sex chromosomes, as it is in humans, but also by environmental conditions such as the presence of hormones, explains Gutierrez.

By exposing genetic males to female hormones, or vice versa, it is therefore possible to create a male that is genetically XX, or a female that is XY or even YY. Such individuals, with the genetics of one sex but the physical characteristics of the other, are referred to as carriers of 'Trojan sex chromosomes'.

In Gutierrez's model, repeated introduction of YY females resulted in an extremely male-dominated population, as all offspring produced from meetings between males (XY) and YY females are male, and many more males are born in subsequent generations. With fewer and fewer females around, the birth rate declined and finally ground to a halt, and the population was extinct within just a few decades. His calculations have been published in the Journal of Theoretical Biology.

But Gutierrez is cautious about trying out his ideas in the real world just yet. "More research is needed to better understand how sex reversal can be efficiently achieved in various potential target species," he says. "The approach is not a quick fix for invasive species, but rather a long-term solution that will require a committed effort over many years."

Non-GM

The idea of controlling an invasive population by manipulating its sex ratio is nothing new, says Gutierrez. However, previous plans required using transgenic organisms, which is undesirable as it carries the risk that the genes will 'escape' into the wild. Using hormones gets round this problem. "With our technique the animals are not genetically modified," explains Gutierrez. "We're not introducing new genes - it's very different."

The approach has numerous advantages, says Samuel Cotton of the University of Lausanne, Switzerland, who has reviewed Gutierrez's theory. "The method only affects the target species, so there is no probability of collateral ecological damage," he notes. "Also, it is reversible - if there are any unwelcome side-effects you can just stop adding YY females."

Gutierrez has joined forces with John Teem of the Florida Department of Agriculture to examine how the strategy might stop the spread of another invasive species - the apple snail - throughout the state's waterways. They are aiming to publish an advanced version of the model later this year, which will allow scientists and policy-makers to assess the suitability of the technique for specific cases.

But whether the issue will receive adequate support is far from certain. "The problem is big, expensive, and the government agencies in charge of it are under-funded," Gutierrez says. "The Program of Research on the Economics of Invasive Species Management had only US$4.9 million to spend between 2003 and 2006. One can only wonder why the agency in charge spends only $4.9 million in four years for a problem that according to conservative estimates costs the United States $200 billion per year."

References

1. Gutierrez, J. B. & Teem, J. L. J. Theor. Biol. 241, 333-341 (2006).
2. Cotton, S. & Wedekind, C. Trends Ecol. Evol. doi:10.1016/j.tree.2007.06.010 (2007).

5 July 2007; | doi:10.1038/news070702-15 / http://www.nature.com/news/2007/070702/full/070702-15.html

Super-eruption: no problem?

Tools found before and after a massive eruption hint at a hardy population.

Katharine Sanderson

Massive eruptions make it tough for life living under the ash cloud. Getty

A stash of ancient tools in India hints that life carried on as usual for humans living in the fall-out of a massive volcanic eruption 74,000 years ago.

Michael Petraglia, from the University of Cambridge, UK, and his colleagues found the stone tools at a site called Jwalapuram, in Andhra Pradesh, southern India, above and below a thick layer of ash from the eruption of the Toba volcano in Indonesia - an event known as the Youngest Toba Tuff eruption.

The tools from each layer were remarkably similar, and Petraglia says that this shows that the huge dust clouds from the eruption didn't wipe out the population of tool-using people. "Whoever was there seems to have persisted through the eruption," he says.

This is the first archaeological evidence associated with the Toba super eruption, says Petraglia, and it contradicts theories that the eruption had a catastrophic effect on the area that its ash blanketed.

Modern man?

Petraglia thinks that modern humans - rather than Neanderthals or other hominins - are the only species that would have been able to persist through an event as dramatic as the Toba eruption. This theory will spur much debate, he admits, because modern humans were not thought to have reached India, from Africa, so long ago. "It's controversial," says Petraglia, "but it makes a lot of sense."

Petraglia and his team compared the tools they found to others from Africa from different periods in this week's edition of Science. The Indian tools look a lot like those from the African Middle Stone Age about 100,000 years ago, when modern humans were thought to have lived, he says. "Whoever was living in India was doing things identical to modern humans living in Africa." Neanderthal toolkits found in Europe are very different, he says. This is more evidence, he says, that the plucky ash-covered inhabitants of Jwalapuram were modern humans.

Stanley Ambrose, from the University of Illinois at Urbana-Champaign, disagrees with Petraglia's conclusions. "It is highly speculative to say the eruption had no impact," he says. Ambrose argues that Petraglia's sample size is too small to make proper comparisons with other tools. And, he adds, "stone artifacts cannot be used to differentiate Neanderthals from African moderns."

Petraglia says he has plenty more stone tools to back up his suggestions, beyond the ones presented in Science. "We have reported only some of our assemblages," he says. He adds that much more work needs to be done on the Indian subcontinent, and much more needs to be learned from comparing archaeological evidence in Africa to that in India.

"The only way to definitively demonstrate the existence of modern humans before and after the eruption in India is by discovering human fossil skulls," says Ambrose. This is something that Petruglia will go some way to agreeing with: "It's true we have to look for fossils," he says. "The search is on."

Reference : Petraglia, M. et al. Science 317, 114-116 (2007).