Scientists have long known that animals change their phenotype (observable characteristics) to cope with the rising temperatures seen in the last few decades.
The most widely documented response has been shifts in the timing of life-history events, according to a recent paper published in the American Naturalist. Examples of life-history events are flight period, reproduction and migration.
A key question, however, is whether these phenotypic changes are evolutionary or nongenetic. In a long-term scenario of rising temperatures, genetic changes (through the mechanism of natural selection) could allow the species to survive whereas nongenetic changes would not.
To answer this question, researchers at the National Oceanic and Atmospheric Administration studied sockeye salmon in the Columbia River. They noted that the salmons, in response to rising temperatures, migrated upstream an average of 10 days earlier compared to the 1940s.
Using water temperature records and data on salmon mortality, they determined that up to two-thirds of the 10-day change is explained by natural selection.
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Evidence of an evolutionary response in Columbia River sockeye salmon is good news, because it appeared to reduce their exposure to potentially lethal river temperatures in recent years, said Dr. Lisa Crozier, lead researcher of the study.
Crozier' study is not the first to document genetic adaption to climate changes.
In 2009, Yale lecturer Carl Zimmer wrote that Arthur Weis, then of the University California at Irvine, collected field mustard seeds in normal conditions and then in drought conditions seven years later.
When he grew the two batches of mustard seeds in identical conditions, Weis discovered that the drought condition seeds were smaller, produced fewer flowers and produced the flowers eight days earlier in spring. In other words, the population of mustard seeds have genetically adapted to drought conditions in less than seven years.
Darwin thought evolution was gradual, and that it would take longer than the lifetime of a scientist to observe even the slightest change. That might be the average case, but evolution can also be very rapid under the right conditions. Climate change is going to be one of those things where the conditions are met, said Weis.
This changing view of evolution has led some researchers to look for evidence that global warming is driving evolution, wrote Zimmer.