GLOBAL warming is already influencing the evolution of some animals, according to research that attributes genetic changes to rising temperatures.

Scientists have identified heritable genetic changes among squirrels, birds and insects that appear to be evolved adaptations to a warmer world.

As average temperatures have increased, the researchers say, so have the lengths of the warmer spring and autumn seasons. This has given a substantial advantage to animals with the genetic ability to vary their behaviour accordingly, influencing the course of evolution.

The evolutionary adaptations observed to date, however, are all related to changing season length, rather than building tolerance to higher temperatures or altered climatic conditions. This means that species are likely to remain vulnerable to extinction as global warming progresses.

In a review published today in the journal Science, William Bradshaw and Christina Holzapfel, of the University of Oregon, highlight several examples of animal species evolving in response to global warming.

The animals are migrating, breeding or developing earlier in the spring, and research has established that this goes beyond normal variation and is influenced by genetic change.

“Over the past 40 years, animal species have been extending their range toward the poles and populations have been migrating, developing or reproducing earlier,” Dr Bradshaw says. “These expansions and changes have often been attributed to ‘phenotypic plasticity’, or the ability of individuals to modify their behaviour, morphology or physiology in response to altered environmental conditions.

“However, phenotypic plasticity is not the whole story. Recent studies show that over the period of recent decades, climate change has led to heritable, genetic changes in populations of animals as diverse as birds, squirrels and mosquitoes.”

Canadian red squirrels are breeding earlier in the year, allowing them to take advantage of earlier availability of the spruce cones on which they feed.

Blackcap birds in central Europe are increasingly migrating to spend the winter in Britain, rather than the Iberian peninsula, and a genetically distinct sub-population that favours this strategy is becoming larger as a result.

Among European great tits, rising temperatures have created selective pressure because the caterpillars on which their chicks feed are maturing earlier in the spring. Tits that can lay their eggs earlier — a trait that is determined genetically — have an advantage, as their chicks can still eat these caterpillars.

In fruit flies, genetic characteristics that are typical of southern, warm-climate insects are becoming more common in northern latitudes.

In mosquitoes living in water caught in the leaves of North American carnivorous pitcher plants, a genetic shift has changed the time at which larvae become dormant in anticipation of winter.

• Global warming could be returning the world to the way it was four million years ago, when sea levels were 80ft (25m) higher than they are today, scientists led by Dr Alexey Fedorov, of Yale University, report in Science.

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