Alpine bee tongues shorten as climate warms

Those increasing temperatures – 2014 was the hottest year on record, and 2015 is on track to top it – are wreaking havoc on the flower populations, say the scientists.

As climate change has warmed the heights of the Rocky Mountains, the anatomy of some specialized bees has changed too, weakening their ancient partnerships with certain alpine flowers. “But if you’re a generalist, short-tongued bee, you’re more likely to run into your resource”.

Tongue size is important in bees because it controls which flowers they can visit for nectar. But bees with long tongues are often considered specialists, meaning they only pollinate flowers with deep corolla tubes – and this can be a beneficial arrangement for both the bee and the plant.

In the midst of a widespread decline in bees, particularly in the United States, a few bumblebees are finding a way to cope: shorter tongues. Bees unfurl their mop-tongue into a flower and slurp up the nectar from the blossom’s depths.

This tactic works best when food is abundant. To compare the older bees with modern ones, the researchers spent successive field seasons on the same mountain peaks netting insects and measuring flower density. “That’s a good thing – they’re responding to these changes in selective pressure”, says Nicole Miller-Struttmann, an evolutionary ecologist at SUNY College at Old Westbury and a co-author on the paper, which was published Friday in the journal Science.

Many co-evolved species have precisely matched traits. In order to better understand why, the researchers studied several high-altitude sites in Colorado. Another species, Bombus sylvicola, saw a drop to just under four millimetres from just over five millimetres.

“It’s a very short period of time to have seen such a strong shift”, said Leif Richardson, a postdoctoral research fellow at the University of Vermont’s Gund Institute for Ecological Economics, who was not involved with the study. Now, climate change could pose even further threats to already vulnerable bee populations.

“They have adapted to diminished resource levels, a major impact of climate change”, writes senior author Candace Galen in an email to the Monitor.

A mismatch between pollinators and their food plants could have negative consequences for plant populations, says Miller-Struttmann. “And it takes less energy to get to them because you don’t have to search them out as much”.

But the change in tongue size does have some benefits.

“Declines in flowering [affect] the majority of the mountain landscape; in these extensive habitats, millions of flowers were lost”. The economic value of bee pollination services ranges from $10 billion to $15 billion. But for now, it’s still unclear how the flowers will be affected. If the bees start to disappear, it could lead to a sharp decline in flowers as well.

“The silver lining is that bees are adapting”. Miller-Struttman agrees but says that is something she plans to look at next.