Climate Got Your Tongue?

Floral biodiversity in the Arctic and in alpine ecosystems worldwide is declining as rising temperatures dry out soils, and in the Colorado Rockies, a new study reports, this has led to bumblebees with shorter tongues. Yes, bumblebees have tongues (actually called “glossa”), and some species have lengthier ones than others.

A long-tongued bee will unroll its glossa deep into long-tubed flowers to lick up nectar, while short-tongued bees will go to just about any bloom to slurp up whatever they can reach. Long-tongued bee bodies are built to feed off long-tubed flowers. For the extra effort it expends growing its lengthy appendage, the bee gets the reward of gobs of sweet, juicy nectar buried in the bottom of the flower that other buzzers miss out on.

So why are these tongues going out of style in a warming West? By comparing bumblebee specimens from 1966 to 1980 with samples from 2012 to 2014, the researchers found that the glossa of two species of long-tongued bees have gotten 24 percent shorter over the last 40 years. As to the cause, the authors point to the loss of millions of flowers in parts of the region.

“If you’re a hungry human going down the highway looking for a place to eat in, say, the middle of Missouri, and there are very few options to choose from, you’ll stop at any exit once you realize the options are slim,” explains Candace Galen, an evolutionary biologist (and native Missourian) who has been studying alpine ecosystems in the Rockies for decades. “You’ll eat fast food that night because you’re starving. Beggars can’t be choosers.”

Short-tongued bees are considered the generalists of their world, as they feed on a wider range of flowers. For short-tongued bees, it pays to visit many flowers quickly, while long-tongued bees go to fewer blooms but get more nectar per visit. Now that there are fewer flowers available, the long-tongued species need to incorporate more types of flowers into their diet—and the less-endowed among them seem to be faring better, not having to expend as much energy to grow a big tongue that is no longer much of an asset.

Galen first thought bee tongues were getting shorter because the insects were getting smaller. Generally, the smaller the body, the shorter the tongue. But in this case, tongues were dropping in size to a much higher degree. so the research team ruled that out. Next, they wondered whether the tubes, or corollas, of alpine flowers were getting shorter over time. That didn’t quite add up either—these bloom on alpine plants like bristlecone pines, which live for hundreds of years. For the trees to have evolved over the past four decades would be astounding. So the researchers nixed that hypothesis, too. They also found that the warmer conditions aren’t hitting long-tubed flower species harder than shorter-flowered plants. What they’ve concluded is that there are just fewer flowers for the bees to feast on than there were in the 1960s and ’70s.

Who knew that bee-tongue length would be an indicator of climate change? This points to the importance of studying specific regions over long periods of time. For scientists, Galen says, it’s unusual these days to work in the same location year after year, even though long-term data sets are incredibly valuable to assess what’s changing and what’s not. Having preserved bee bodies from the ’60s and ’70s allowed us to get a better picture of how global warming is affecting the region and its inhabitants, floral and apian alike.