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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>http://opinionator.blogs.nytimes.com/2010/03/09/breezy-love-or-the-sacking-of-the-bees/?hp<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<!-- date updated --><!-- <abbr class="updated" title="2010-03-10T00:03:08+00:00">— Updated: 12:03 am</abbr> --><!-- Title -->
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12.0pt'><img width=561 height=261 id="_x0000_i1049"
src="cid:image002.jpg@01CAC048.9722D0A0"><o:p></o:p></span></font></p>
<h3><b><font size=4 face="Times New Roman"><span style='font-size:13.5pt'>Breezy
Love, or the Sacking of the Bees<o:p></o:p></span></font></b></h3>
<!-- By line -->
<address><i><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>By
<a href="http://opinionator.blogs.nytimes.com/author/olivia-judson/"
title="See all posts by OLIVIA JUDSON">OLIVIA JUDSON</a><o:p></o:p></span></font></i></address>
<address><i><font size=3 face="Times New Roman"><span style='font-size:12.0pt'><o:p> </o:p></span></font></i></address>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Birds do
it. Bees do it. Beetles, bats and light summer breezes do it.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>I refer,
of course, to that raunchiest of sex acts: the pollination of flowers.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>When it
comes to sex, plants have more headaches than the rest of us. One problem is
that they can’t travel about to find a mate — they are, after all,
rooted to the spot — so they have to depend on intermediaries to bring
egg and sperm cells together. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>For
mosses and ferns, the intermediary is water. For conifers like pine trees and
cypresses, the intermediary is wind. But for most flowering plants, the
intermediaries are animals.<br>
<br>
Flowering plants are the largest, most successful group of plants on the planet
today. There are thought to be more than quarter of a million different species
— nearly 10 times more than all the other types of plants added together.
(To put things in perspective, the number of living species of fish, amphibians,
reptiles, birds and mammals combined is less than 58,000.) The flowering plants
include roses and waterlilies, grasses and oak trees, tulips and orchids. They
include, in short, most of the plants that come to mind when one thinks of
vegetation. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>It was not
always thus. Before the mid-Cretaceous, 100 million years ago or so, flowering
plants were scarce: conifers and their relations ruled the landscape. But then,
for reasons that are not well understood, flowering plants upstaged all others,
and the Earth came into bloom. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Flowering
plants were not the first to seduce animals into spreading their pollen for
them. Fossils suggest that some earlier groups of plants, now extinct, had
evolved a dependency on insects like scorpionflies. Nonetheless, the earliest
flowers appear to have been pollinated by insects, and the full-scale
blossoming of flowering plants coincides with the rise of animals as
go-betweens. Bees, for example, buzzed onto the scene with flowering plants;
the evolutionary history, and success, of both groups is intimately linked. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>The
appearance of flowering plants brought a new flamboyance to the planet. Flowers
pollinated by animals tend to be big and colorful; they often smell. (To a
human, flowers pollinated by bees typically smell pleasant; flowers pollinated
by flies tend to smell foul, like rotting meat.) Often, flowers offer something
for the animal to eat — a sip of nectar, perhaps. Sometimes, they provide
heat. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>(One
plant that heats its flower is Philodendron solimoesense, an Arum from the
South American tropics. In doing so, it turns itself into an assignation hotel
for scarab beetles. The beetles arrive in the evening, spend the night feeding
and mating, spend the morning recuperating and head off to a new flower later
on — complete with pollen from their host. Sure enough, the heat saves
the beetles energy. Beetles in a heated flower don’t have to use as many
calories to keep warm as they would if they spent the night outdoors.)<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Yet, from
time to time, flowering plants abandon their animals, evolving instead to throw
pollen to the wind. Wind-pollination — if you’re a vocabulary
fiend, the technical term is “anemophily,” meaning lover of wind
— has evolved at least 65 times in flowering plants, and around 10
percent of the species do it. Indeed, <a
href="http://opinionator.blogs.nytimes.com/2010/03/02/evolution-by-the-grassroots/">as
I mentioned last week</a>, many grasses are pollinated by the wind.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>It’s
not clear what causes this transition, though there are several ideas. One is
that it happens in plants that, although generally pollinated by insects,
already have a small capacity for wind pollination — small, light pollen
grains, and flowers that can, in principle, catch pollen if it floats past on a
breeze. Then, the balance between insects and wind can easily shift. In a
tropical forest, for example, the advantages of insects are great: they provide
highly targeted pollen-delivery in a complex milieu. But in big open spaces,
the wind may do a better job — especially if the climate is inhospitable,
and insects are few. Such circumstances may cause a shift away from traits that
lure insects, and enhance those that seduce the wind.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>A plant
that has sacked bees or other insects can make its flowers smaller, less
colorful and more aerodynamic. Liberated from the expense of making nectar, it
can make more pollen instead. A bee, after all, can only carry so much pollen
at once. The wind is not so limited. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>And
wind-pollinated plants tend to produce huge quantities of pollen. Whereas
animal-pollinated plants produce a median of 3,450 pollen grains for every
ovule, wind-pollinated plants produce almost 10 times as much. No wonder
wind-pollinated plants are the chief causes of eye-itching, nose-tickling human
misery. (It’s not just the anemophilous flowering plants that are to
blame, though. Wind-blown cypress pollen is a major cause of allergies in some
parts of the world.)<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>This
massive production of pollen is usually put down to the inability of wind to
make reliable deliveries. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Charles
Darwin himself suspected the wind of being a fickle and inefficient messenger,
and that view has largely held until this day. But there is little actual
evidence that wind-pollinated plants have more difficulty getting themselves
fertilized than other plants do. (Indeed, plants seem adept at plucking pollen
of the right species out of the breeze. How they do this isn’t known.)
Moreover, in animals, large numbers of sperm tend to evolve when competition
between different males to fertilize a female’s eggs is fierce. In many
wind-pollinated species, plants flower all together, and for a brief time.
Perhaps wind-pollinated plants face greater competition from their rivals.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>But
whatever the causes, I’m glad that most plants have not sacked their
bees. In a world pollinated only by gusts and breezes, spring would be less
beautiful. And, for many of us, it would also be more tortured.<o:p></o:p></span></font></p>
<p><em><i><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Notes:</span></font></i></em><o:p></o:p></p>
<p><em><i><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>I
have taken species numbers, for flowering plants and all other plants, and for
the number of vertebrate species, from table 2.1 of Baillie, J. E. M.,
Hilton-Taylor, C. and Stuart, S. N. 2004. “A Global Species
Assessment.” IUCN Publications. It can be downloaded <a
href="http://www.iucn.org/knowledge/publications_doc/publications/">here</a>.</span></font></i></em><o:p></o:p></p>
<p><em><i><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>The
reasons for the surge to dominance of flowering plants have been extensively
debated. A nice summary of the hypotheses is provided by Berendse, F. and
Scheffer, M. 2009. “The angiosperm radiation revisited, an ecological
explanation for <st1:City w:st="on"><st1:place w:st="on">Darwin</st1:place></st1:City>’s
abominable mystery.” Ecology Letters 12: 865-872. </span></font></i></em><o:p></o:p></p>
<p><em><i><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>For
scorpionflies serving as pollinators for now-extinct groups of plants, see Ren,
D. et al. 2009. “A probable pollination mode before angiosperms: Eurasian
long-proboscid scorpionflies.” Science 326: 840-847 and Ollerton, J. and
Coulthard, E. 2009. “Evolution of animal pollination.” Science 326:
808-809. For early flowering plants being dependent on insects, see, for example,
the discussion in Crane, P. R., Frils, E. M. and Pedersen, K. R. 1995.
“The origin and diversification of angiosperms.” Nature 374: 27-33.
See also Hu, S. et al. 2008. “Early steps of angiosperm-pollinator
coevolution.” Proceedings of the National <st1:place w:st="on"><st1:City
w:st="on">Academy of Sciences</st1:City> <st1:country-region w:st="on">USA</st1:country-region></st1:place>
105: 240-245. </span></font></i></em><o:p></o:p></p>
<p><em><i><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>For
the evolution of bees and their relationship to the evolution of flowering
plants, see Danforth, B. N. et al. 2006. “The history of early bee
diversification based on five genes plus morphology.” Proceedings of the
National <st1:place w:st="on"><st1:City w:st="on">Academy of Sciences</st1:City>
<st1:country-region w:st="on">USA</st1:country-region></st1:place> 103:
15118-15123. The association between pollinators and showy flowers is well
known. For foul smells being produced by flowers pollinated by flies, see
Jürgens, A., Dötterl, S. and Meve, U. 2006. “The chemical nature of fetid
floral odours in stapeliads (Apocynaceae-Asclepiadoideae-Ceropegieae).”
New Phytologist 172: 452-468. For beetles and assignation hotels in the form of
Philodendron solimoesense, see <st1:City w:st="on"><st1:place w:st="on">Seymour</st1:place></st1:City>,
R. S., White, C. R. and Gibernau, M. 2003. “Heat reward for insect
pollinators.” Nature 426: 243-244.</span></font></i></em><o:p></o:p></p>
<p><em><i><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>The
number of transitions from animal pollination to wind pollination is given in
Friedman, J. and Barrett, S. C. H. 2009. “Wind of change: new insights on
the ecology and evolution of pollination and mating in wind-pollinated plants.”
Annals of Botany 103: 1515-1527. This paper also discusses the general
shrinkage of flower features in wind-pollinated plants as opposed to
animal-pollinated plants, and provides an overview and discussion of the
hypotheses for what could cause such transitions. </span></font></i></em><o:p></o:p></p>
<p><em><i><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>For
the idea that the transition is most likely in insect-pollinated plants that
already allow occasional wind pollination, see Culley, T. M., Weller, S. G. and
<st1:City w:st="on"><st1:place w:st="on">Sakai</st1:place></st1:City>, A. K.
2002. “The evolution of wind pollination in angiosperms.” Trends in
Ecology and Evolution 17: 361-369. See also Ackerman, J. D. 2000.
“Abiotic pollen and pollination: ecological, functional, and evolutionary
perspectives.” Plant Systematics and Evolution 222: 167-185; the author
discusses many of the features of wind-pollinated plants, and presents evidence
that wind pollination is less haphazard than had previously been thought. For
the argument that wind pollination takes off when insects are scarce or in some
other way unreliable, see Cox, P. A. 1991. “Abiotic pollination: an
evolutionary escape for animal-pollinated angiosperms.” Philosophical
Transactions of the Royal Society of <st1:City w:st="on"><st1:place w:st="on">London</st1:place></st1:City>
B 333: 217-224.</span></font></i></em><o:p></o:p></p>
<p><em><i><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>For
the large numbers of pollen grains produced by wind-pollinated plants as
compared to insect-pollinated plants, see Cruden, R. W. 2000. “Pollen
grains: why so many?” Plant Systematics and Evolution 222: 143-165. For
wind pollination and allergic reactions see, for example, D’Amato, G. et
al. 2007. “Allergenic pollen and pollen allergy in <st1:place w:st="on">Europe</st1:place>.”
Allergy 62: 976-990. </span></font></i></em><o:p></o:p></p>
<p><em><i><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>For
<st1:City w:st="on"><st1:place w:st="on">Darwin</st1:place></st1:City>’s
skepticism about the efficiency of wind pollination, see chapter 10 of Darwin,
C. 1876. “The effects of cross and self fertilization in the vegetable
kingdom.” John Murray. This is available from <a
href="http://gutenberg.net">Project Gutenberg</a>. For wind-pollinated plants
being able to pluck the “right” pollen from the air, see Linder, H.
P. and Midgley, J. 1996. “Anemophilous plants select pollen from their
own species from the air.” Oecologia 108: 85-87. The relationship between
high levels of sperm competition and high sperm numbers in animals is well
documented. See, for example, Parker, G. A. 1990. “Sperm competition
games: raffles and roles.” Proceedings of the Royal Society of <st1:City
w:st="on"><st1:place w:st="on">London</st1:place></st1:City> B 242: 120-126.
For the possibility, and some evidence, that large pollen numbers are due to
competition between males, not to the inefficiency of wind as a means of
delivery, see the Friedman and Barrett paper cited above. This paper also
provides evidence that wind-pollinated plants often flower together, a
mechanism which could both increase the efficiency of wind-pollination and
increase the chance of competition from rivals. </span></font></i></em><o:p></o:p></p>
<p><em><i><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Many
thanks to Jonathan Swire for insights, comments and suggestions.</span></font></i></em><o:p></o:p></p>
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