Length of bee tongues

This received via Dave Stocks at the Gilroy, CA, ‘The Buzz’, reprinted
there from Bee Thinking, which took it from the online publication


Living on a mountain is hard for bees and flowers. It’s cold. There’s
extreme weather. And new research has found it getting even harder for
both flowers and bees to make a living in alpine environments lately.
Scientists compared over 40 years of mountain bumblebee and flower records
on three Colorado mountains and found major decreases in both bees and
flowers. But they also found clear evidence of rapid evolution by the bees,
suggesting it.s not time to give up on mountain bumble bees just yet.
Entomologists and botanists get teased about traveling the world, meeting
interesting insects and plants, and then killing them. But it’s a morbid
habit that pays off; it creates a long-term, stable record of the
biological past. Museum collections may look like a creepy charnel house to
outsiders, full of corpses, pins, and mothballs. Our libraries of dead
things become a book of evolutionary change for future scientists to read.

Preserving organisms from taxonomic or ecological studies lets us travel
back in time. People are always interested in having their data looked at
and reanalyzed in a different way, a way that they hadn’t thought about
previously. That is one of the great things about having open access data,
said Dr. Nicole Miller-Struttmann, lead author on the new bumble bee study.

To investigate how flowers and bumble bees changed, a team of scientists
dug through over 40 years of records. They tracked down thousands of bumble
bee specimens collected on mountains in Colorado between 1966 and 1980, and
compared them to bumblebees collected in the same areas between 2012 and
2014. They also used herbarium specimens of flowers collected during
similar time frames and surveyed flowers in the field.

Plants on mountains often have very narrow temperature tolerances; too much
heat can reduce flowering. On one of the mountains in the study, between
1960 to 1985, only 12 percent of the years were hot enough to reduce
flowering. Since 1985, 48 percent of years were too hot for flowers that
bumblebees typically forage on.

Since 1970, the total number of flowers available for bees on the mountain
study sites declined by 60 percent overall. What did that mean for bees?

Over 95 percent of bees in the study regions between 1966 and 1980 were
just two species of long-tongued bees. These bees specialize in flowers
with a narrow, elongated tubular shape. Their long tongue means they are
able to reach the nectar hidden at the bottom of a flower and can muscle
out their shorter-tongued relatives. This is an example of coevolution,
where two species reciprocally affect each other over evolutionary time.

Bees collected from 2012 to 2014 were different, though. The long-tongued
species of bumble bees declined by 24 percent. At the same time, warming
temperatures and changes in flowering plants allowed some lower altitude
bees to live at higher mountain elevations. The entire community of bumble
bees changed. Long-tongued bumble bees responded to the scarcity of flowers
by becoming less selective; the range of plants they foraged on changed
significantly and included flowers with no long nectar tubes.
The scientists wondered if the bees physically changed too, and measured
body length and tongue length on their historic and modern bee specimens.
How do you measure a bee’s tongue? Miller-Struttmann explains: They tuck
their tongue back into their body, so they sort of fold it back up along
their chin, I guess you could say. We had to re-hydrate historic specimens,
and then fold the tongue out, and then measure it under a microscope with

What no one expected was that the tongues of long-tongued bees would get
shorter. A lot shorter.  A 24 percent decrease in tongue length is really
dramatic, says Miller-Struttmann. That was in 40 years, in 40
generations, I should say, because these bumblebees only have one
generation a year. That’s a pretty short period of time to see such a
dramatic shift. Bumble bee bodies also got slightly smaller, but not as
much as the tongues shrank. The research team did not find changes in the
depth of the flowers bumble bees were visiting. The bees shape changed,
but the flowers didn’t.  Building and maneuvering a big tongue takes energy, and bees with shorter
tongues may have done better at diverting that energy into more babies. In
the short term, the bumble bees seem to be hanging on. But what about
longer term?

Right now, bumblebees and the plants they historically fed on are
mismatched physiologically. The bees may not be as good a pollinator for
those plants, which could cause further declines in flowers. In the long
term, perhaps they will also evolve, but they’re much longer-lived species.  Their generation time is decades, not yearly. Change will be slower or may
not happen at all.

Dr. David Inouye has researched flowers and alpine bees at the Rocky
Mountain Biological Laboratory for decades. He said, This study is a great
example of the value of archiving data an example of a change in bumble
bees that is unexpected, and would not have been discovered without access
to historical data. We have evidence from elsewhere in the Rocky Mountains
that bumble bee queens of eight species have moved up 230 m in altitude over
about the same time span, and these kinds of changes in bumble bee
communities will have interesting consequences over both ecological and
evolutionary time scales.

This study also highlights a common problem for mountain or other remote
refuges as the climate warms, the places where plants and animals=
thrive move slowly away from the areas we’ve designated for their conservation. By
increasing areas set aside for nature, or making sure we have connections
between isolated nature refuges, we can try to help bees and plants adapt
to our new warmer world.


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