Monday, August 4, 2014

The meandering of the Amazonian water lily from there to here

BBC Radio 4 is in the midst of a fascinating 25-part series, Plants: From Roots to Riches, on the history of botany from the perspective of the Royal Botanic Gardens at Kew.  Kew is of course Britain's botanical pride and joy, the world's largest collection of living plants.  The original gardens were established in the early 1700's, an unparalleled beneficiary of the expanding British empire as plants were collected around the world and sent to the Kew repository even before it was established as a national botanical garden in 1840.

As promised, the program sees botanical history through Kewian lenses -- the program on the rubber trade, for example, doesn't mention what Britain's successful transplantation of smuggled rubber trees from Brazil did to the Brazilian rubber trade and Brazil's economy, a bit of sanitized history as told by the victor.  Still, the program is fascinating, with the history of many individual plants, including the cycad (Encephalartos altensteinii) that arrived at the gardens in 1755, before Linnaeus devised his naming system, or notes from Charles Darwin on plants he brought to the garden.  Only at Kew could this long history be told.

And then there's the Amazonian water lily (now called Victoria amazonica, it was originally named Victoria regis after the queen).  In 1837 botanist Robert Schomburgk found this plant in the Berbice River as he was exploring British Guiana.  The plant is called "water maize" in its native habitat, where it grows abundantly.  The leaves can be up to 3m, or 9.8ft across, and sturdy enough to hold a small child.  The flowers are  huge, colorful and highly scented -- sometimes.  The plant produces 40 - 50 leaves in a single season.

Flowering Victoria amazonica,
Amsterdam Hortus Botanicus, Ellie Swindells; Wikipedia
Schomburgk sent seeds to Kew and to collectors elsewhere, starting a race among botanists to be the first to grow the plant and see it to flowering.  Schomburgk's seeds germinated the first year, but it was too late in the season for the plant to flower, so it died without going to seed.  Eventually seeds were sent from the Demerara River, and Kew was successful in getting them to flower in 1849 (The Royal Botanic Gardens, Kew; Bean et al., 1908).  The plant is a perennial in its native habitat but is treated as an annual in non-tropical climates; at Kew they have managed to grow it from seed every year since 1849.  It grows extraordinarily quickly, attaining its enormous size, from seed, every year.

Amazonian water lily at Kew Gardens; The Telegraph
As Bean et al. wrote in 1908: 
As one might infer from its enormous dimensions and extraordinarily quick growth, the Victoria regis is a gross feeder.  Every fresh plant has to be supplied with several cartloads of good loam, enriched by rotted manure.  The water is kept at first at a temperature of about 80 degrees F., deducted to 75 degrees as the plant becomes strong and established.  Perhaps the most important desideratum is abundant and unrestricted light.  With these needs supplied, the cultivation of this noblest of aquatics presents no difficulty, except that in late years a troublesome fungus has often disfigured the leaves.  
Flowers are a variety of pinks and whites, and the plant has an unusual mechanism of pollination.  The plant's first blossoms are large and white, and female.  The flowers open in the evening, and smell of pineapple, and actually heat up. The scent beckons to beetles, and when they sit on the flower, transferring pollen to the stigma, the flower closes around them.  The beetles are attracting mates, and then mating inside the flower, all easier at higher than ambient temperatures. The flower reopens the following night but it is pink, it has lost its smell and it is now male, its anthers mature and ready to shed pollen.  The beetle picks up the pollen and flies to the next white flower, still a female, waiting to be pollinated (source).

This is interesting in its own right.  Hermaphroditic flowers, with both male and female organs, aren't uncommon, but flowers that are one and then the other are less so. Here's an extremely successful plant in its native habitat, with a reproductive trick that it shares with few plants.

This could be, like any trait, an example of what Ken discussed in his final post on the mythology of natural selection about the meandering path from then to now.  Does this pollination mechanism have an adaptive advantage?  Is it due to natural selection, meaning that water lilies that are male or female, or hermaphrodites, with two sets of sex organs, reproduced less successfully than the V. amazonica in this plant's natural habitat long ago, allowing V. amazonica to overrun the habitat?

Or, alternatively, did some of these flowers, those with this dynamic gender ability, perhaps for locally specific reasons in a scenario we can only guess at, increase in frequency over eons just by chance?  Here a change and there, at some other time, another change until eventually the plant acquired this ability to change gender?  If or how much was aided by specific natural selection for the trait, and what kind of selection are unknown, and may not even be knowable.  Indeed, this may not be the most energy efficient way to reproduce, nor the only way the plant could reproduce.  It just happens to be the way that currently works.

Modified from Google Images images
It is tempting to view what we see today as examples of stages 'on the way' from ordinary two-sex plants to this kind of  ones, as if a kind of inevitability.  Rather, and here we repeat a figure from the last part of our recent series on natural selection, the evolution of what we see today could have had so many local reasons as to appear essentially random, relative to a straight development to today's system. The idea of an essentially straight path from there to here, so tempting, is in fact in many ways a teleological view of evolution that assumes, at the least, that the same kinds of selection, mutation, ecology and so forth are serially occurring everywhere there are these plants.  It's the sort of argument even Charles Darwin made in viewing various sorts of 'incomplete' hermaphrodism in barnacles.   One might argue that these extrapolations are true, that evolution will ineluctably drive these plants (and barnacles) to their end-points as we see them today (let's not quibble about why they'd be viewed as end-points). But plausibility then sneaks under the tent to be accepted as truth.


Hollis said...

Neat post. I'm enjoying the BBC series by the way -- highly recommended and thanks for the tip. Still thinking about your twitter question ... I was puzzled by the concept of change in sex. It's not uncommon for the sex organs of bisexual flowers (also common, in fact the "primitive" state) to mature at different times, probably helps promote out-crossing. Nor is it uncommon for flowers to close at night and open again in the morning. I searched a bit online, then had the clever idea of looking in my systematics textbook ;-) Victoria is protogynous -- flowers have both pistils and stamens, the former mature first. So not a sex change as in animals, but whatever -- if people think it's cool and appreciate it, semantics hardly matter!

Anne Buchanan said...

Glad you're liking the BBC series. I'm enjoying it as well. Thanks for your more precise description of what's going on! I wish I could find a time-lapse video of the inside of the flower, as parts wither and mature, but since it would be closed during much of that time, I guess that's too much to ask!