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signals, he says. For example, a cell that promotes blood vessel growth in the tumour’s vicinity will also benefit other precancerous cells (Proceedings of the National Academy of Sciences, vol 103, p 13474). The recognition that cancer cells cooperate has implications for understanding how the disease develops, and may lead to new approaches to therapy. “For example, you could change the micro-environment of a tumour so that the diffusion chemicals don’t travel so far,” says Axelrod. locations – proceeds more efficiently for all players if they cooperate, and this can occur without the players developing conscious strategies. “It’s well established that tumour cells grow by diffusing growth factors into the neighbouring tissue,” says Axelrod. Some cells don’t have the “full deck” of mutations needed to produce every growth factor, overcome host defences and seed new tumours, but they can help each other by contributing the missing abilities and growth EVEN phytoplankton are letting us down when it comes to global warming. These microscopic ocean-dwelling plants, which were thought to be gobbling up atmospheric carbon dioxide, are apparently not doing as well as was hoped. In the past, satellite images of ocean colour were the main tool for measuring photosynthetic biomass: the greener the ocean the more CO 2 was being taken up by the phytoplankton. This idea now seems to be misleading. Peter Strutton of Oregon State University and colleagues studied phytoplankton fluorescence in the tropical Pacific using data from 12 years and 58,000 kilometres of ship transects and found that the phytoplankton are making far less chlorophyll than expected. They reason that in nutrient-poor waters like the tropical Pacific, phytoplankton are starved of nitrates and iron. Because of this they produce a pigment-protein complex that is not chlorophyll but shows up just as green in satellite images. They calculate that this means 2.5 billion tonnes less CO 2 is being absorbed each year than was thought (Nature, vol 442, p 1025). Green is not always good GLOBULAR clusters, often regarded as the most boring denizens of our galaxy, have just become a lot more interesting. Rogue, hot stars have been discovered inside them. The tens of thousands of stars that make up each globular cluster were all thought to have formed at the same time, with exactly the same composition, from a single spherical cloud of gas. Then, two years ago, a hint of a rogue population of hot, helium-rich stars was detected in the largest known globular cluster, Omega Centauri. This cluster, however, is known to be exceptional. “I just thought, OK, the very weird globular cluster is being weird again,” says Alison Sills of McMaster University in Hamilton, Ontario, who studies the clusters. Now, Giampaolo Piotto’s team at the University of Padua in Italy has found similar helium-rich stars in another, more ordinary cluster, NGC 2808, suggesting that such stars could exist in all globulars. The team thinks that about a 100 million years after each cluster formed, some of the larger stars sent out a gentle wind laced with helium and heavier elements, which settled at the centre of the cluster and coalesced into a second generation of chemically enriched stars. Similar wind-formed stars could also explain mysterious ultraviolet emissions from elliptical galaxies, says Piotto, as some of them would be hot enough to radiate UV light. SPIDERS are not known for their caring, sharing nature. Unlike social insects, it is rare for arachnids to live in cooperative groups. Now a colonial species of spider has been discovered that uses group tactics to hunt. Leticia Avilés and colleagues from the University of British Columbia in Vancouver , discovered the spider, Theridion nigroannulatum (pictured above guarding egg sacs), in rainforest in eastern Ecuador. The spiders, which live in nests that house up to several thousand individuals, hunt by hanging sticky silk threads from low-lying leaves. When an insect blunders into the silk, a group of spiders drop down and wrap more threads around it, paralysing their prey with venom and carrying it back to the nest to share with others in the community. “It’s truly remarkable,” says Avilés. “Not only do the spiders cooperate during the kill, but if the prey is large they take turns carrying it back.” Another arachnid first is the observation that females come in two sizes. In social insects, this represents a division of labour, with large females becoming soldiers and smaller ones gathering food, for example. In T. nigroannulatum size dimorphism could reflect different reproductive tactics, with females attempting to get a head start on egg-laying by maturing earlier, at a smaller size (Biotropica, DOI: 10.1111/j.1744-7429.2006.00202.x). CANCER cells may not have foresight, but between them they can hatch strategies of attack. An analysis of how these strategies develop is providing insights into the disease which may lead to new treatments. Because cells in a tumour differ in their mutations and needs, you can use “game theory” to understand how they interact, says Robert Axelrod, a political scientist at the University of Michigan, Ann Arbor. The “game” – to grow a successful tumour that can spread to new JASON WARF/SCIENCE PHOTO LIBRARY LETICIA AVILÉS How cancer cells cooperate to achieve our downfall www.newscientist.com 2 September 2006 | NewScientist | 15 Along came a colony of spiders Clusters reveal their hot secrets
