[PCA] Fwd: [Pollinator] Do Flowers "Defend" their pollen?

De Angelis, Patricia patricia_deangelis at fws.gov
Mon Mar 23 11:56:03 CDT 2015


Though this study focused on European species, several members of the
mallow family are native to the United States.

---------- Forwarded message ----------
From: Peter Bernhardt <bernhap2 at slu.edu>
Date: Wed, Mar 18, 2015 at 10:37 AM
Subject: [Pollinator] Do Flowers "Defend" their pollen?

Here's a recent publication for people interested in how bees store the
pollen they collect and the impact this storage can have on natural rates
of flower pollination.  Does the shape and sculpturing of the pollen grain
restrict where certain bees can store them?  For many flowers pollination
can't occur if their grains are packed into the corbicula of a member of
the Apidae as the grains are cemented and packed with liquid (generating
early hydration and cytoplasm death) and the receptive stigma of the flower
is never in the right position to contact either corbicula.  This
interesting interpretation uses one of the most common European
wildflowers.  Remember also that members of the mallow family (Hibiscus and
Alcea) produce some of the physically largest pollen grains in Nature.

--Peter

Just spines—mechanical defense of malvaceous pollen against collection by
corbiculate bees
Klaus LUNAU, Vanessa PIOREK, Oliver KROHN, Ettore PACINI
Apidologie (2015) 46:144–149

Abstract – Bee-pollinated plants face the dilemma that bees do not only
transport pollen grains between flowers as
pollen vectors but also collect large amounts of pollen that is withdrawn
from pollination. Here, we show that pollen
of the common hollyhock, Alcea rosea, is mechanically protected against
collection by corbiculate bees. In a
laboratory setup, bumblebees did not collect the large, sticky, and spinose
pollen grains of A. rosea from artificial
flowers unless following manipulation of the spines or the pollenkitt.
Following removal of the sticky pollenkitt or
bending the spines by vortexing the bumblebees readily collected the
pollen. Our results show that the pollen of
A. rosea is not bitter-tasting or toxic, but mechanically protected by the
spines against being collected by corbiculate
bees. Light microscopic (LM)-micrographs indicate that the long spines of
malvaceous pollen grains are not covered
by pollenkitt suggesting a new mechanism of mechanical defense against
collection: pollenkitt-free spines and
lipophilic pollenkitt prevent compacting pollen grains into pollen storage
organs of corbiculate bees. The experi-
mental data fit to observations at flowers of A. rosea and other malvaceous
plants that honeybees and bumblebees are
densely dusted with pollen but discard the pollen while packing it into
their corbiculae.
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