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  EurekAlert 8 Jun 06
Recent, rapid climate change is driving evolution of animal species
University of Oregon

National Geographic 8 Jun 06
Global Warming Is Spurring Evolution, Study Says
Richard A. Lovett for National Geographic News

German birds are changing migration patterns. Canadian red squirrels are reproducing earlier in the year. Mosquitoes in Newfoundland remain active longer into August.

Traditionally, scientists have viewed such changes simply as behavior modifications in the face of a changing environment--in this case, global warming.

But scientists say these shifts provide mounting evidence that for some animals, global warming is sparking genetic changes that are altering the ecosystems we live in. The effect is most striking in the northern latitudes, where climates are becoming more and more like those in the south, researchers say.

"Over the past 40 years, animal species have been extending their range toward the poles, and populations have been migrating, developing, or reproducing earlier," said William Bradshaw, an evolutionary geneticist at the University of Oregon in Eugene.

These shifts aren't simply a response to warmer summers but instead reflect recent and rapid changes to the climate at large, Bradshaw and colleague Christina Holzapfel argue in tomorrow's issue of the journal Science.

"The emphasis on summer temperatures is just plain wrong," Holzapfel said. "Midsummer temperatures in Florida aren't all that different from Fairbanks, Alaska. This is about lengthening growing season and the timing of seasonal events."

Warming and Evolution

Many animals use changing daylight as a signal for when to mate, migrate, or hibernate. But as global warming makes Alaska more like Mississippi, the cues animals once relied upon will no longer match the climate.

Bradshaw and Holzapfel cite as an example the European blackcap, a bird that traditionally breeds in Germany and then migrates southwest for the winter to Spain and Portugal. Some of these birds have begun to migrate west to England, which now has a suitable winter climate, the researchers say. In the spring, these British birds can beat their Spanish cousins back to Germany, getting dibs on the best nesting sites. Moreover, Bradshaw and Holzapfel note, the east-west migration pattern is instinctive, indicating that it's now embedded in the British birds' genes.

The upshot, Holzapfel says, is that some animals will be able to adapt to continued climate change, while others will have considerable difficulty.

"Large animals like polar bears will probably do very poorly," she said. "They have a long life cycle, so it takes them relatively long to adapt genetically." Over time, she said, "[ecological] communities will become completely different."

Animals and Natural Cues

Other ecologists agree. The matching of organisms' life cycles to their environments is essential for survival, says Steven Running, forestry scientist at the University of Montana in Missoula.

Global warming, he says, is altering the optimal time for temperature-sensitive activities without changing the daylight cycle in any given place. The result is a mismatch between the altered climate and the genetically programmed cues upon which organisms currently rely.

The ability of plants and animals to evolve in the face of these changes, Running said via email, "may well define what species are winners and losers in adapting to rapidly changing climates."

EurekAlert 8 Jun 06
Recent, rapid climate change is driving evolution of animal species
University of Oregon

Oregon researcheres say organisms are adapting to altered seasons and not to direct effects of increasing temperatures

Rapid climate changes over the past several decades have led to heritable, genetic changes in animals as diverse as squirrels, birds and mosquitoes, according to University of Oregon evolutionary geneticists. Writing in the "Perspectives" section of the June 9 issue of SCIENCE, William E. Bradshaw, professor of biology, and Christina Holzapfel, biology research associate, show that diverse animal populations have changed genetically in response to rapid climate change.

These genetic changes are in response to altered seasonal events and not to the expected direct effects of increased summer temperatures. Global warming is proceeding fastest at the most northern latitudes, resulting in longer growing seasons while simultaneously alleviating winter cold stress without imposing summer heat stress. In short, northern climates are becoming more like those in the south.

"Over the past 40 years, animal species have been extending their range toward the poles and populations have been migrating, developing or reproducing earlier," said Bradshaw. "These expansions and changes have often been attributed to 'phenotypic plasticity,' or the ability of individuals to modify their behavior, morphology or physiology in response to altered environmental conditions."

However, adds Holzapfel, "phenotypic plasticity is not the whole story. Studies show that over the past several decades, rapid climate change has led to heritable, genetic changes in animal populations."

Bradshaw and Holzapfel provide a number of examples of these changes: Canadian red squirrels reproducing earlier in the year; German blackcaps (birds) are migrating and arriving earlier to their nesting grounds; and, North American mosquitoes living in the water-filled leaves of carnivorous plants are using shorter, more "southern" day lengths to cue the initiation of larval dormancy.

In contrast, the authors write that no studies have found genetic changes in populations relating to the generally expected direct effects of increasing temperature. There are no examples in animal populations of genetic changes that have either increased the upper limits of heat tolerance or increased the optimal temperature for growth, development and reproduction.

"Small animals with short life cycles and large population sizes will probably adapt to longer growing seasons and be able to persist," said Bradshaw. "However, populations of many large animals with longer life cycles and smaller population sizes will experience a decline in population size or be replaced by more southern species."

"Consequently, genetic shifts in the timing of seasonal events should precede genetic shifts of thermal optima or increased heat tolerance over evolutionary time," said Holzapfel. "That is the pattern that is emerging.

Questions remain about the relative rates of environmental and evolutionary change. However, it is clear that unless the long-term magnitude of rapid climate change is widely acknowledged and effective steps are taken to mitigate its effects, natural communities that we are familiar with will cease to exist."
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