One of the most common social contracts between
plants and their pollinators is to offer a mixture of sugars in solution as a
reward for the pollination service. The flowers have their nectaries placed so
that the pollinators have to dig deep. Some deeper than others.
The result of the flower variation is the
specialization of the pollinators. Some pollinators rely on capillary rise like
the hummingbird that curls its tongue into a tube (1). Others, butterflies for
example, suck, while bees dip.
Enquiring minds in the mathematics and engineering
departments of MIT spotted that the fast supping of nectar required by
inveterate nectar drinkers has to be done rapidly as to kick back and take a
leisurely drink is likely to catch the eye of a predator. As the sugar content
increases so does the viscosity of the nectar and so the big question arises:
is the drinking style and sugar content of the nectar provided a match?
The answer is yes (1,2). Sugar contents are almost at
the optimum for the particular drinking style. So dipping is done with a higher
sugar content than sucking, which in turn, is higher than best for capillary
rise.
Note though, that the content is less than the optimum.
The suggestion is that plants are keeping the pollinators hungry so they’ll
keep coming back (2), but that seems unlikely, certainly in the case of bees
who are taking it back for processing and would require lower viscosities for pumping
it in and out of their stomachs in an easy fashion.
I suspect that the concentrations may be nearer
optimized than suggested if the whole picture is considered. Co-evolution for a
symbiotic result is really quite beautiful.
- http://www.pnas.org/content/early/2011/09/19/1108642108
- http://www.bbc.co.uk/news/science-environment-15068454
