Global warming really does change everything, it seems. Its effects can be seen at huge scales – such as droughts and floods – but also in things as small as a bee's tongue. Bumblebees living in the mountains of Colorado are evolving shorter tongues, and a new study indicates climate change is the culprit.
As if insufficiently burdened with cynicism about their flying capacity, some alpine bumblebees took aboard the extra weight of long tongues to reach the nectar inside deep flower cups. Following reports of a decline in long-tongued bees, Dr. Nicole Miller-Struttmann from the State University of New York compared modern specimens of two species (Bombus balteatus and B. sylvicola) with those collected between 1966 and 1980.
In Science, Miller-Struttmann reports that the shortening of their tongues is real. After ruling out changes in overall body size, coevolution with flowers and the effects of new species invading the bumblebees' territory, Miller-Struttmann concluded that the shortening is a result of a warming climate.
Hotter summers have reduced the number of flowers appearing in Colorado's alpine meadows. This has included the deep-cupped flowers the bumblebees prefer, leaving them with no alternative other than to sup from the shallower vessels. With fewer flowers available, short-tongued generalists have survived best.
“There are two main advantages to having a short tongue,” Miller-Struttmann told IFLScience. “While bees with short tongues may be less efficient when foraging on deep flowers, they are adept at visiting many different kinds of flowers and have more options when it comes to food sources.” Long tongues can actually get in the way of sipping nectar from shallow flowers. Miller-Struttmann added that there is also an energy cost to growing and maintaining an impressively long tongue.
Miller-Struttmann said it is not known if the local flower decline has hurt bumblebee numbers. “We do not know the collection effort (the number of hours the scientists collected bees) for the past studies, so we cannot test for changes in total abundances.... However, we do know that selection has demographic costs. It stands to reason that lower abundances of preferred flowers may result in fewer bumble bees, at least in the short term, until they are able to adapt to their shifting environment.”
Hot summers may be initiating a vicious circle for the deep-cupped flowers. Miller-Struttmann pointed out that they depend on long-tongued bees for pollination. If these disappear due to the flowers' rarity, deep-cupped species will struggle to survive even if temperature conditions suit them.
“A morphological mismatch between the bumble bees and their preferred host plants could result in lower seedset, shorter flowers and potentially population declines in the long term. Many alpine plants are long-lived, so the effects of a potential change in selection may not be immediately apparent,” she said.
We might care as little for bees' tongues as we do for other parts of their anatomy, but the findings demonstrate how rapid climate change can disrupt ecological partnerships.
Miller-Struttmann told IFLScience that flower abundance changes may be a contributing factor to wider bee population decline, but added, “I do not want to understate the impact of neonicotinoids, which are also having negative effects on some bee populations.”