In a comment on last week’s post on orchids, reader André Schuiteman, whose team discovered the first night-blooming orchid described in that post, calls our attention to a remarkable film showing a different orchid, Angraecum sesquipedale (“Darwin’s orchid), being pollinated by the long-tongued moth, presumably Xanthopan morgani. It’s a rare sight indeed since pollination occurs only at night. Remember that Darwin, confronted by this flower with its remarkably long nectar spur, theorized that there must be a moth in the forest whose tongue was long enough to reach the nectar (that has to happen to effect pollination, since the moth’s body has to contact the orchid flower itself). This moth was finally discovered in 1903.
The video was made in Madagascar by a friend of mine, Phil DeVries from the University of New Orleans, a remarkable—and, as you’ll see, intrepid—naturalist, and author of the two-volume Butterflies of Costa Rica and their Natural History.
It’s really lovely to see how excited Phil gets when he finally sees the pollination. Those are the juicy moments that every naturalist lives for.
Most excellent.
Science, got to love it!
T’was a thrill watching Xanthopan do its thing, almost like a sexual act. How can anyone see this and still not believe that evolution is true?
‘Cause goddidit?
It’s interesting to think about the selection pressures on both the orchid and the moth over time–if the moth grew a tongue that was too long, it could drink without pollinating, and the orchids would not reproduce. If the nectar tube were too long, then the moth would get nothing.
How did they settle on this length? Is it impractical for the moth to have a longer tongue? That would put a high end on its length, and the orchids which were the correct size would then reproduce. Also, since the nectar is not available to other insects, these moths are assured success (to the orchid’s benefit).
Why assume the length is “settled”? We’re only seeing a little time-slice of the evolutionary sequence!
Ha Ha, of course! It’s never over. It’s so easy to think of the current world as ‘the end’ when it’s just as slice, as you say. . .
but still, if that tongue were any longer that moth couldn’t get off the ground
I would surmise that if a moth has a longer than average proboscis then it will indeed only help reproduce those orchids that have a longer than average nectar tube thus giving them (these orchids) a reproduction advantage.
This would lead to a rise in the number of longer-nectar-tube orchids And once you have enough of them in the orchid population it would give an advantage to those moths with a longer proboscis as they can reach the nectar of more orchids.
So my guess would be the longer proboscis evolves first (by small increments of course) through natural variation and/or genetic drift (I guess it would be correct to term it that way at the beginning of the cycle as it would not yet have an adaptive advantage for the moth until the orchid population adapts with longer tubes).
Of course it is 5AM around here so my hypothesis could just be a lot of tosh and I would welcome any information correcting it from Jerry or one of his educated readers.
Errrh… invert nectar tubes and proboscis moth and orchids to have the longer nectar tube evolving first as, like you pointed out, a longer proboscis first would not help in reproducing the orchid, but a longer nectar tube would not prevent it (indeed, by not sating the appetite of the moth it might even give the orchid an advantage by ensuring the moth goes to other flowers sooner).
Like I said, 5AM her, let’s hope there are no other brainfarts in my posts this morning.
Another thought–if there was a period when orchids had shorter or differently-lengthed tubes, then it would be to the advantage of the moth to have a longer tongue, but not to all the orchids. A long-tongued moth could feed at all the orchids but only would pollinate some of them.
I wonder if the tongue just got longer and longer, and the orchids responded, until the moths reached the point of just-almost-completely-absurd, and then the selection pressure eased.
just shows evolution has no foresight. it just goes down the path without concern that it would lead to absurdity. and i don’t think the current lengths are stable or at the physical limit of what’s possible. why not a 2 feet long proboscis? no reason why the moth could not evolve stronger wings too.
There are many other species in the genus Angraecum, most of which have much shorter spurs than A. sesquipedale. Some are only a few millimeters long. So it is unlikely that there is a general trend towards longer and longer spurs. In this respect, A. sesquipedale seems to be an exception, along with a few related species such as A. longicalcar, which may have a 40 cm long spur, surpassing even A. sesquipedale.
It is probably not the case that any moth species is entirely dependent on one particular orchid species. Therefore it is not likely that those orchids are capable of exerting much selection pressure on the moths. It needs further research to establish if and why A. sesquipedale is an exception.
Phil, if you are reading this, congrats again!!! What a cool thing to see.
Probably even Darwin could not have predicted that another species of Angraecum, A. cadetii from Reunion, is not pollinated by a moth but by a cricket. It is the first flowering plant in which this has been observed. See here for more details and some film footage.
It seems plausible that A. cadetii evolved from a moth-pollinated species, perhaps in response to gradual extinction of suitable moths. Claire Michenau, who discovered the cricket pollination phenomenon, notes that long-tongued moths are absent from Reunion and found that there are at least two more Angraecum species on Reunion that are not pollinated by moths but by birds. To put this in context, the orchid genus Angraecum contains more than 200 species, most of which seem obviously moth-pollinated (white flowers, long spurs).
> Micheneau
CGI.