Climate change forces rapid evolution in mountain bumblebees

Scientists in Colorado have found the tongues of alpine bumblebee populations are getting shorter to make up for a reduction in flowers, caused by warming temperatures.

Erigeron growing in the Rocky Mountains. Image: MorgueFile
Erigeron growing in the Rocky Mountains. Image: MorgueFile

In a research paper published in Science, researchers showed that the populations of two alpine bumblebee species (Bombus balteatus and B. sylvicola) in the Rocky Mountains have rapidly evolved as they have been forced to change their foraging habits.

The paper explains that long-tongued alpine bumblebees coevolved with alpine flowers with elongated tubular petals in a mutually beneficial relationship. But as warming temperatures and drier soils have caused floral resources to decline, the bumblebees have incorporated shallower flowers into their diets – and their tongues are growing shorter to compensate.

Over 40 years tongue length across the two bee populations fell by nearly 25 per cent. As there was a dramatic fall in the number of flowers that are only available to long-tongued individuals, shorter-tongued individuals that can feed on nectar from many types of flowers would be more likely to survive and pass on their genes to their offspring, over time causing a decline in average tongue length.

The researchers explained that alpine habitats are considered "canaries in the coal mine" for global warming, with warmer temperatures causing a worldwide decline in flowering in alpine and arctic habitats. On Pennysylvania Mountain, one of three mountains in the study, total flowers had declined by 60 per cent since the 1970s, the researchers found.

They concluded that although long-tongued bee populations are undergoing widespread decline, changes in foraging habits could help alpine species cope with climate change.

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