Archive for August, 2017

Mad for Orchids

Sunday, August 27th, 2017

    Who knew that orchids are the world’s largest plant family?  Ten percent of all plant species are orchids!  

    I had always thought of orchids as exotic, even rare plants.  Until recently, that is, when my friend Laura invited me to watch a fascinating nature show with her, PLANTS BEHAVING BADLY.  What a title!  How can a plant behave badly? 

     Well, according to David Attenborough, the show’s host and one of my heroes, the title alludes to tricks some orchid species employ to lure the pollinators they need.  Certain conniving orchids draw in their pollinating insects with a promise of sex or food, and then fail to deliver.  

     A plant that promises sex?  

     Attenborough introduces us to the bee orchid flower.  The flower structure of this orchid greatly resembles a female bee.  So when male bees emerge from the ground after hibernation, eager to mate, many of them think they’ve spotted what they’re looking for in the orchids nearby.  

     Clasping the flower in a passionate embrace, the male bee is disappointed when he realizes that this is not a female bee after all.  When one or two more attempts to mate with flowers on the same plant result in failure, he flies off to try his luck with another orchid plant nearby.  

     So the bee’s disappointment is the orchid’s success.   When the bee gives up on an individual orchid plant and tries other orchid plants nearby, he spreads pollen more widely, a practice known as cross-pollination.  Cross-pollinations makes for greater genetic diversity   than does self-pollination, where the pollen remains on the same plant.  That clever orchid!

     And false promises of food?  Unlike most orchid species, which draw pollinators by producing nectar that they love, some orchids only appear to offer nectar.  Certain orchid species have evolved shape and coloring that strongly resemble the shape and coloring of orchid species that do offer nectar.   These trickster orchids fool insects into thinking they have found a source of nectar.  

     Not finding any nectar in the orchid flower, the insects quickly move on to another nearby plant.  This orchid strategy of disappointment again results in success for the plant!  It has tricked the insect into cross-pollinating.  What a trick to play on unsuspecting insects.

     While about a third of orchid species practice some form of deception to bend pollinators to their will, says Attenborough, most orchid species do deliver the nectar (but maybe not the sex) their pollinators are after. These thousands of orchid species have developed a vast range of features that include hairs, tails, horns, fans, crests, even teeth and warts–that are very attractive to the particular pollinators who have evolved with them.

     Perhaps the most astonishing orchid-pollinator match known, Attenborough tells us, has quite a history:  In 1862, Charles Darwin was sent an orchid from Madagascar.  Called Angraecum sesquipedale, this beautiful, star-shaped orchid had a nectary a foot long!  (The nectary is a tube, at the bottom of which is the nectar the pollinator wants, along with pollen the orchid wants the pollinator to take).

     Darwin was incredulous!  What insect could possibly have a proboscis long enough to pollinate such an orchid! Darwin surmised that there must be a moth that does have such an absurdly long proboscis.  But he never found the orchid’s pollinator. 

     Twenty years after Darwin’s death, in 1907, a moth was discovered in Madagascar that had a proboscis about as long as the Angraecum sesquipedale‘s nectary!  But it was not until 1992, 85 years later, that this moth, Xanthopan marginii praedicta was actually observed pollinating the orchid.  Attenborough treats us to thrilling night-time footage of the giant moth unfurling its incredibly long proboscis and inserting it into the orchid’s foot-long nectary!  Also wonderful, we see the photographer, the first to catch the action on film, dancing in joy!–April Moore

 

Home | About | Blog | Contact | Newsletter

Earth Connection is proudly powered by WordPress
Entries (RSS) and Comments (RSS).