Adapting to Climate Change

Photo: Denis Crawford of Graphic Science CAN'T TAKE THE HEAT: Drosophila birchii, the Australian rainforest vinegar fly, was unable to evolve adaptations for a hot, dry environment in laboratory tests. Average global temperatures are expected to rise by 5°C or more over the next century. That's a lot of heat to handle for thousands of plant and wildlife species that already have been affected by a seemingly paltry 0.60°C temperature change over the past century. Eggs hatch and flowers bloom earlier, and butterflies are shifting their ranges northward. Ecologists have gathered ample quantitative evidence that global warming changes the way animals eat, breed, and interact.1 But how and if they will evolve is another question altogether. Early findings suggest that evolution may depend on what organisms start out with genetically. For some species, such as the Australian rainforest vinegar fly, Drosophila birchii, rapid climate changes may be too much for their genes to handle. Geneticist Ary Hoffmann and colleagues at La Trobe University, Melbourne, demonstrated that this moisture-dependent insect doesn't have the genetic variation needed to adapt to the arid conditions that further climate changes will likely induce.2 And, like forested landscapes worldwide, D. birchii's habitat is fragmenting. "Genetic variation becomes incredibly important when you have a species that has a restricted distribution," says Hoffmann. "Most organisms have to either evolve in place or go extinct," says University of Oregon researcher William Bradshaw. Conducting a 30-year study of photoperiodic response in the pitcher-plant mosquito, Wyeomyia smithii, Bradshaw and colleague Christina Holzapfel have long sought an evolutionary response to global warming.3 Photoperiodic response is the genetically controlled use of day length as a cue to regulate seasonal behaviors such as winter dormancy. In this case the mosquitoes are adapting well to climate change. By responding to shorter days, the mosquitoes enter dormancy later than their ancestors did. But researchers warn against extrapolation. University of Alberta biologist Stan Boutin led the discovery of a genetically controlled shift toward earlier breeding among red squirrels in Yukon, Canada, the first evidence of an evolutionary response to global warming in mammals.4 Yet, says Boutin, "The verdict is out on whether other organisms in northern environments can show the same genetic change." It appears there's no reprieve for Australia's vinegar fly, at least. SERENDIPITOUS SCIENCE Hoffmann's team didn't set out to study the genetics of global warming. Rather, they were hunting for desiccation resistance genes. They performed a standard, all but intense, artificial selection experiment, exposing flies to desiccative stress (less than 10% humidity) until all but 10% to 20% had died, and then bred the survivors. The scientists expected the flies to evolve, but even after 30 generations of selection, the flies were no better suited for drier conditions than at the outset. Desiccation resistance of Drosophila lines during selection. Click to view enlarged graph (12K) Surprised, the researchers wondered if the flies had somehow been affected by laboratory living. Subsequent tests proved otherwise. Unlike pitcher-plant mosquitoes and red squirrels, D. birchii is narrowly distributed and already adapted to extreme conditions. Its genetic variation for desiccation resistance has likely been tapped dry, so to speak. The rainforest fruitfly is also unlike other Drosophila species, including its widespread cousin and well-known model organism, Drosophila melanogaster, which shows dramatic selection responses. Hoffmann says that conclusions about evolutionary potential to respond to global warming or any other selective force, when derived from studies of widely distributed species, may not be applicable to narrow-range species. Further, conservation biologists often use molecular measures of overall genetic variation as an indicator of genetic good health and the ability to evolve. In this case, they'd be wrong. The vinegar flies have just as much overall genetic variation as widespread species. "It's a very variable species," says Hoffmann. "You just don't have genetic variation for the trait that matters." Leslie Pray (lpray@nasw.org) is a freelance writer in Leverett, Mass. References 1. T.L. Root et al., "Fingerprints of global warming on wild animals and plants," Nature, 421:57-60, 2003. 2. A.A. Hoffmann et al., "Low potential for climatic stress adaptation in a rainforest Drosophila species," Science, 301:100-2, July 4, 2003. 3. W.E. Bradshaw, C.M. Holzapfel, "Genetic shift in photoperiodic response correlated with global warming," Proc Natl Acad Sci, 98:14509-11, 2001. 4. D. Réale et al., "Genetic and plastic responses of a northern mammal to climate change," Proc R Soc Lond B Biol Sci, 270:591-6, March 22, 2003. function sendData() { document.frm.pathName.value = location.pathname; result = false if (document.frm.score[0].checked) result = true; if (document.frm.score[1].checked) result = true; if (document.frm.score[2].checked) result = true; if (document.frm.score[3].checked) result = true; if (document.frm.score[4].checked) result = true; if (!result) alert("Please select") return result; } .myradio{background-color : #94bee5} Please indicate on a 1 - 5 scale how strongly you would recommend this article to your colleagues? Not recommended 1 2 3 4 5 Highly recommended Please register your vote

Adapting to Climate Change

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Photo: Denis Crawford of Graphic Science
CAN'T TAKE THE HEAT: Drosophila birchii, the Australian rainforest vinegar fly, was unable to evolve adaptations for a hot, dry environment in laboratory tests.