18 May 2013

Repost: Utricularia: Aquatic carnivorous plants that evolved vacuum traps


Note: This entry was originally posted here on 27 February 2011. With all of the recent wonderful news regarding the publication and analysis of the Utricularia gibba genome and the implications of the evolution of its minimal genome, I thought it worthwhile to repost this entry and remind ourselves the other ways in which bladderworts are amazing and interesting. See elsewhere (here is ok) for coverage of the genome research or read the paper!
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"Hi." Trap of Utricularia inflata, clearly showing
the door, trigger hairs, and concave walls.
Scale bar = 500 μm
Source: Vincent et al., 2011.
Utricularia, commonly known as the bladderworts, is a genus of approximately 230 species of carnivorous plants that have evolved an amazing suction trap to supplement their nutrient requirements by trapping and digesting convenient little arthropoid or crustacean packets of nitrogen, phosphorous, and other essential chemicals. Not all species are aquatic, as this cosmopolitan genus has also evolved species with lithophytic (growing in or on rocks), epiphytic, and terrestrial habits.

The rootless aquatic species are most notable for their tiny underwater bladder-shaped traps dotting the web-like system of stolons like aquatic chandeliers. Each trap is only a few millimeters long or less and possess a trap door surrounded by sensitive hairs that trigger the trap door mechanism to open, quickly sweeping the water - and any tasty prey contained therein - adjacent to the trap into the bladder. Keep in mind that each trap is only two cell layers thick when considering the pressure differentials and forces involved in prey capture.

Gazing upon this wondrously evolved botanical curiosity, naturalists in the 19th century thought that it was a passive system as comically illustrated in F. E. Lloyd's 1942 book on carnivorous plants (see below). Charles Darwin and others thought prey was simply enticed into entering the trap, much like a mouse entering a passive mousetrap. Since that time, and thanks to Lloyd's research in the early 20th century, we now know that the bladder traps of Utricularia are much more complex, involving the active setting of a trap and a rapid response once triggered, as illustrated in Lloyd's figure (below), which can only be described as the potential inspiration for the elaborate and beguiling board game Mouse Trap. Rube Goldberg would be proud!

Source: F.E. Lloyd. 1942. The Carnivorous Plants. Waltham, Mass.: Chronica Botanica Co.
The description is too long to reproduce here, but the following amused me: "...which allows the lever l to swing
downwards when the door is actuated again by, it is confidently hoped, a second mouse. In the meantime, the mouse
first caught can employ his time admiring the interior effect, and possibly suggest improvements." (pg. 267)
So by the mid-20th century, we had a pretty good idea of how these traps worked. Water is pumped out of the trap, producing the familiar "set" concave wall appearance. An unlucky crustacean, perhaps a Daphnia, swims too close to the trigger hairs, which relays that signal to the trap door, which swings open so quickly, no one had been able to quantify it before now. And here's where the exciting new research comes in. Physicists decided to record prey capture using high-speed cameras and measure the morphology of the door as it opens. The best thing about this, I believe, is that they put all of their supplemental material on YouTube.






The above video from the new article shows a copepod from the genus Cyclops being trapped by a Utricularia inflata bladder. The whole process occurs in less than one millisecond and is thus one of the fastest plant movements known. The poor little copepod seems utterly stunned. And no wonder! Olivier Vincent at the Laboratoire Interdisciplinaire de Physique, University of Grenoble and colleagues estimated that fluid velocities entering the trap can reach 1.5 meters per second (approximately 3.4 miles per hour) with maximum fluid accelerations of 600g. (Most humans lose consciousness at 4-6g.) Furthermore, in the video above you'll notice the copepod swirls down and around in the trap. The authors propose an interesting idea, that the trap morphology propels prey forward, then down into a swirling motion, preventing the immediate escape before the trap door closes again.

More impressive is the work they did investigating the door morphology as it opens. I can only imagine how precise this microscope, camera, and laser setup had to be in order to capture the exact moment when the door buckles and lets water flow in:






The also produced a dynamic simulation of the door opening:






So there we have it. Amazing new research adds to our understanding of one of the most unique carnivorous plant capture mechanisms. We've come a long way from Darwin's day and I certainly hope there's more to uncover. I'll leave us with just one more video, produced directly by the authors and posted on YouTube:







References:

Vincent O, Weißkopf C, Poppinga S, Masselter T, Speck T, Joyeux M, Quilliet C, & Marmottant P (2011). Ultra-fast underwater suction traps. Proceedings. Biological sciences / The Royal Society PMID: 21325323

27 January 2013

Deliciously named orchid cultivar



Another orchid on the kitchen table is blooming; this time it's the deliciously named cultivar Cycnoches cooperi 'Dark Chocolate' × 'Dark Fudge'. Thanks to these lovely little flowers, I'll now be able to voucher this specimen and include it in my phylogenetic work.

The interesting thing about this genus and its allied genera is that the flowers are unisexual and display sexual dimorphism where the characteristics of the male and female flowers are noticeably different. These here are the male flowers. You can tell by the narrow labellum at the top of the flower and the very long column below the labellum. It was that extraordinary column that gave the genus its common name swan orchids - there's a quite clever illustration at the bottom of the second to last page in this article that might help you visualize why the name is appropriate.

It has been suggested that plant vigor, amount of sunlight, or other environmental factors may lead to whether the plant invests its resources in presenting female flowers. A plant must be capable of supporting seed production if it is going to give up on the possibility of producing male flowers with relatively cheap pollen instead. Luckily for the swan orchids, the molecular "choices" that decide whether a flower is male or female do not decide the fate of all flowers for that year or season. Different inflorescences flowering at the same time can have opposite sex flowers as seen in figure 6 in this article (the photo by Katherine B. Gregg). Gregg's work in the 1970s is the last that I know of in Cycnoches to try and identify what combination of environmental patterns might be generating the plant's phenotypic plasticity. This kind of work has hit a new stride lately in population ecology (here's just one example in alligator weed). Might be an interesting project for someone to work on. And the study organisms aren't half bad to look at!

29 September 2012

The carnivorous plant with catapult traps


Drosera glanduligera (pimpernel sundew) shown here in a figure from the
new paper describing the fast-acting catapult traps (Poppinga et al., 2012).
Creative Commons Attribution License.
As usual, I'm late to the party and many other outlets have already written about this fascinating new paper published in PLoS ONE; such is the nature of the captivating world of carnivorous plant research. I'll try to place the new article in a bit more context.

First, the study organism: Drosera glanduligera, the pimpernel sundew, an Australian native, was first described in 1844 by Johann Georg Christian Lehmann who was cataloging and describing new species found in the collections of the botanical garden that he established and directed in Hamburg (now called Alter Botanischer Garten Hamburg). My botanical Latin needs a good refresher, but at a quick glance it appears to me that Lehmann noticed enough to write down that the marginal tentacles of this species are larger, but that's the only observation he recorded. Indeed, as you can see in the photo above, the marginal tentacles are much longer than the glue-tentacles closer to the center of the leaf lamina (more on this later).

Drosera regia, king sundew.
My plant in cultivation.
It turns out that, at least with this species, nothing more was recorded on what is apparently a fascinating trapping mechanism more analogous to the fast snap trap action of the Venus flytrap swiftly snatching a meal as seen here. That is until Richard Davion began making new field observations in 1974 when he wasn't even ten years old yet and published them in the 1990s in the relatively low circulation newsletter of the Carnivorous Plant Society of New South Wales. This underscores the importance of publishing new observations in journals where your work might get noticed. Davion later contacted two authors of the current study, the Hartmeyers, in 2003 and asked them to corroborate his findings. Within two years they confirmed Davion's observations and presented a film titled, "Drosera: Snap-Tentacles and Runway Lights," at the International Carnivorous Plant Society conference in 2006 that summarized their findings. (The video can be seen in full on YouTube courtesy of the ICPS.)

Snap tentacles: Everyone is excited about this research - and rightly so - but what exactly are snap tentacles and how do they differ from regular tentacles on sundews? On most sundew species like this Drosera regia above and to the right, there is one kind of tentacle: a few-celled stalk supporting a multicellular, glandular, globular head. They vary in length from the center to the edge of the leaf but not in overall morphology. They produce and rely on a viscous mucilage to retain captured prey until the tentacles slowly move (in some species, if at all) and direct the prey toward the digestive glands at the center of the lamina. This can take minutes, even half an hour depending on temperature. The snap tentacles, on the other hand, produce no mucilage and typically have a faster movement. The multicellular head is modified and looks more like a spatula or a pillow resting on oversized spoon (or maybe like a catapult?). They quickly flip unsuspecting prey up and into the center of the remarkably sticky mucilage produced by other tentacles. In milliseconds the prey can reach a maximum velocity of 0.17 m/s and a maximum acceleration of 7.98 m/s. Before it can think or react, it's deposited in the lamina where it's immobilized and often suffocated by the mucilage. Any struggling is futile as other slower tentacles reposition the prey nearer the digestive glands. A few days later after the plant's enzymes have done their work, meal time is complete and new leaves are unfurling, awaiting new dinner guests.

About two years ago, two of the authors of the current study, Siggi and Irmgard Hartmeyer, published their findings on over 100 Drosera taxa in the Carnivorous Plant Newsletter while investigating snap tentacle morphology. They concluded that many species of Drosera from multiple points on the established phylogeny of the genus have snap tentacles of some kind at some point in their ontogeny that vary in how swift the response is. It's important to note, however, that in the 2010 paper they set aside the tentacles of Drosera glanduligera as something wholly different since it was the fastest and the mechanism wasn't quite clear. This may be the reason why we can refer broadly to snap tentacles and flypaper traps on all the species but this one alone has been granted the new term catapult-flypaper-trap.

For their part of the new study, Irmgard and Siggi cultivated the plants, captured new HD film, and created this documentary to accompany the paper's release. Now this is effective science communication (in German with captions in English). If you want to skip the beginning and see the plant in action, make your way to about the 5:00 mark.



So that's cool! A catapult that helps deliver prey in the center of the trap. What else did they find? I'm glad you asked. These tentacles move by some pretty awesome mechanisms since they're moving so quickly - did you watch the video? It completes that swing from laying on the ground to delivering the prey to the hungry center of the leaf in as little as 75 milliseconds. In their investigation, the research team found that these snap tentacles actually deform beyond the ability to "reset" in a resting position to fire once again like the Venus flytrap can. They hypothesize that the cells in the hinge zone actually buckle from the stress involved with the movement - nature's one use only device.

In the discussion, they spend a good bit of real estate on hypothesizing on the mechanism involved: is it rapid water movement from one side of the tentacle to the other or loss of turgor pressure in combination with what would essentially be the release of stored potential energy by a sudden geometric change or curvature inversion not unlike this child's toy (oh, you know you remember annoying your parents with one of those.) But they didn't find any noticeable inversion. This may not be all that different from other tentacle movement (and the initiation of movement in the Venus flytrap) where the acid growth hypothesis is supported. Simply, in acid growth a signal would cause H+ ions to be pumped out of the cell into the cell wall space where proteins in the cell wall matrix known as expansins loosen at an acidic pH (higher H+ concentration). That allows the cells to increase in size very rapidly. If you do this on only one side of the tentacle, the lower surface, the result would be rapid bending inward. There are ways to inhibit the transporters associated with acid growth, but it might take the skills of a fine surgeon to delicately and strategically place the inhibitors on the tentacles without prematurely triggering them!

Regardless, there are plenty of possibilities here for future research, much of which was identified by the authors themselves in the last few paragraphs. Congratulations all around for such an attention-grabbing paper that was even blamed, in part, for slowing down the PLOS website:





References:
Poppinga, Simon, Siegfried R. H. Hartmeyer, Robin Seidel, Tom Masselter, Irmgard Hartmeyer, & Thomas Speck (2012). Catapulting Tentacles in a Sticky Carnivorous Plant. PLoS ONE, 7 (9): e45735. 10.1371/journal.pone.0045735

Hartmeyer, Irmgard, & Siegfried R. H. Hartmeyer (2010). Snap-tentacles and runway lights: summary of comparative examination of Drosera tentacles. Carnivorous Plant Newsletter, 39 (4), 101-113.

19 September 2012

Oeceoclades gracillima: won't you crawl inside?



Oeceoclades gracillima
Don't you just want to crawl inside?

Oeceoclades gracillima (Schltr.) Garay & P.Taylor is an orchid native to Madagascar that has stunning maroon and black mottled foliage which is hard to capture properly on film, but you can see one of the better images here. (In case you were wondering, you pronounce the genus name ee-see-o-CLA-deez.)

I picked this one up from Michel Orchid Nursery when they were at the orchid show and sale at Longwood Gardens in March 2012. I'm so happy it finally flowered as this means I'm able to dry and press a specimen for a voucher and begin working on isolating and sequencing DNA from the leaves and flowers on the other inflorescence. It's not the prettiest flowering orchid around - the flowers are mostly small and drab - but it's got character elsewhere in the leaves.

For those of you with a sharp eye who follow the blog because of my interest in carnivorous plants, you'll notice that this species had originally been named Eulophia gracillima by the German orchid specialist Friedrich Richard Rudolf Schlechter in 1913. That name was supplanted in 1976, however, by the new combination when Leslie Andrew Garay and none other than the Utricularia expert Peter Taylor!

Taylor was also the co-author of another combination, Oeceoclades roseo-variegata, which according to the Kew World Checklist is now a synonym of O. gracillima. The former is still in use, however, and was how my plant came labeled from the nursery.

Beauty is in the eye of the beholder, I suppose, and this little flower has a wonderful little nectar spur. Overall, a great, compact orchid that was really easy to cultivate.

07 August 2012

Tweeting the 9th biennial International Carnivorous Plant Society conference


ICPS conference participants
Participants browsing the sales area at the 8th ICPS conference (2010) in Leiden, Netherlands. Photo by kitkor.
At the end of the week I'll be on my way to my second International Carnivorous Plant Society conference, the last being held two years ago in Leiden, Netherlands. (When they said International, they meant it.) It's a relatively convenient trip from Ohio to Seekonk, Massachusetts where the New England Carnivorous Plant Society will host the international conference, the first time it's been back in North America since 2006.

Unless there are unforeseen technical difficulties, I plan to tweet along with the presentations, just like I did for several of the Botany 2012 sessions I attended. If you're so inclined, you can follow me on Twitter where I'll be using the hashtag #ICPS12 if anyone else wants to join in (#ICPS2012 was already taken by a few recent tweets on a physics conference). I've also made a resolution to do a better job at updating the blog during the conference, but of course this may prove to be difficult.

It will be great to see so many colleagues and friends, especially those I've known only through our weekly Board meeting chats via Skype for the North American Sarracenia Conservancy. I'll finally be able to meet many of you in person!

Get ready for some awesome carnivorous plant content fed into your social media.

31 July 2012

Peer-review system failed in controversial gay parenting study


In early June a new social science study was published online ahead of print on the purported differences in children who were raised by gay parents as opposed to those raised by heterosexual parents ("How different are the adult children of parents who have same-sex relationships? Findings from the New Family Structures Study" by Mark Regnerus). Concerns were immediately raised about the study's sample, methodology, analysis, and therefore results. Most notably, the study characterized anyone who ever had a same-sex relationship after having a child as thereafter a gay father or lesbian mother regardless of whether they parented the child together as a couple. If you're studying the effects of same-sex relationships on the rearing of children, don't you think this would be an important detail to pay close attention to? This is just bad science.

And a new review by the journal that published the piece agrees. The editor of the journal assigned a member of the journal's editorial board to assess how such a "bullshit" paper got published in the first place. Where did our system break down? The report and the piece in The Chronicle of Higher Education is fairly damning and underscores how important our job as scientists is when we put on our reviewer hats:
In his audit, he writes that the peer-review system failed because of “both ideology and inattention” on the part of the reviewers (three of the six reviewers, according to Sherkat, are on record as opposing same-sex marriage). What’s more, he writes that the reviewers were “not without some connection to Regnerus,” and suggests that those ties influenced their reviews.
I've not yet been asked to put a reviewer's hat on - nor should I until I'm further along in my studies - but I've seen a few publications through the review process and I've seen my PIs, good, thoughtful PIs, calmly refuse to accept manuscripts because of conflicts of interest. I know it's tough sometimes; the academic nature of science is incestuous and we collaborate or have connections with just about everyone in our narrow fields who is qualified to give our manuscripts a thorough review. Or at least that's how it feels sometimes. But that's no excuse. If you're asked to review a manuscript of an author with whom you have a conflict of interest, kindly refuse to accept, simple as that.
In reality, only two respondents lived with a lesbian couple for their entire childhoods, and most did not live with lesbian or gay parents for long periods, if at all. The information about how parents are labeled is in the paper. Regnerus writes that he chose those labels for “the sake of brevity and to avoid entanglement in interminable debates about fixed or fluid orientations.” Sherkat, however, called the presentation of the data “extremely misleading.” Writes Sherkat: “Reviewers uniformly downplayed or ignored the fact that the study did not examine children of identifiably gay and lesbian parents, and none of the reviewers noticed that the marketing-research data were inappropriate for a top-tier social-scientific journal.” [emphasis mine]
And I suppose this is where it all comes down to: flawed peer-review in this case failed to identify severely flawed social science.

30 July 2012

Thecostele alata wants to give you a hug



I received this cute little orchid from Gines Orchids last week for my research on genera allied to Dipodium and Cymbidium. Like most species in this group of orchids, Thecostele alata (above) is native to Southeast Asia. Those two slender upper petals sort of look like they're reaching out to give you a hug, don't they? And is it just me or does the column resemble the head of a floppy-eared dog (at least from this angle)? Perhaps I've been staring at this for too long.

12 June 2012

New study on carnivorous plants makes headline writers batty

sciseekclaimtoken-500248d42bb9e


Before we get started, let me say that I forgive those who write headlines like pollution makes carnivorous plants go vegetarian and carnivorous plants go vegetarian in response to pollution and new study finds that pollution turns carnivorous plants into vegetarians. They know not what they do. It's also tempting to go after the flashy, attention-grabbing headline. Just try to do a better job next time, ok? And while we're on the topic, let us thank those that presented reasonable titles, like the one by Liat Clark at Wired.co.uk: carnivorous plants capture less prey in polluted bogs. Thank you for getting it a bit better! It would also be a terrible oversight if I neglected to mention that the Southern Fried Scientist took this issue to task a few days ago. Bravo!

So, on to the science at hand. What's all the fuss about?

Triangle Lake Bog, Ohio
Drosera rotundifolia at Triangle Lake Bog, Ohio. Photo by kitkor.
ResearchBlogging.orgDrosera rotundifolia, the round-leaved sundew. Or common sundew. Or "bloody hell that thing is everywhere." And it is: North America, Europe, Asia... Here in Ohio it is the most common species of Drosera that you'll bump into - the other being Drosera intermedia, but several sites it had been known from have now been developed. For those unfamiliar with carnivorous plants, you might be peripherally aware that it is thought that these species have evolved in nutrient-poor environments. Given this idea and our knowledge that most species possess a good deal of phenotypic plasticity in response to environmental cues, researchers decided to further test earlier experimental observations that Drosera rotundifolia reduced its investment in carnivory (as measured by stickiness in units of force used to remove a piece of filter paper from the leaf) when grown in the presence of more nitrogen (Thorén et al., 2003).

Here in the new study, the researchers, a team including J. Millett of Loughborough University, B. M. Svensson and H. Rydin of Uppsala University, and J. Newton of the Scottish University Environmental Research Centre, were more interested in the relative amount of nitrogen that came from prey captured by normal means and from the roots as a result of increased nitrogen available from atmospheric deposition due to increased air pollution.

Briefly, the authors identified three bogs in Sweden that represented a gradient of mostly pristine to somewhat polluted in terms of nitrogen deposition. Fifteen specimens were removed from the bogs, dried, and analyzed for stable isotopes of nitrogen. Once they had their isotope data, all they did was subtract surrounding Sphagnum isotope data from Drosera and divide that by (insect - Sphagnum), where insect represents the mean isotope number for prey captured on the plant at the time of collection. And there's an easy ratio!

So conclusions from this? Well, the authors state it very clearly in the abstract, which many of the headline writers must have missed: "Drosera rotundifolia plants in this study switched from reliance on prey N to reliance on root-derived N as a result of increasing N availability from atmospheric N deposition." (emphasis mine) No, headline writers, these plants were not "OMG BECOMING VEGETARIANS!" Wouldn't that be a plant eating plant matter? And, as strange and wonderful as nature is, we have two possible examples in Nepenthes ampullaria and Utricularia purpurea where the former seems well-adapted to catch leaf litter and the latter appears to primarily cultivate algae in its bladder-like aquatic traps. No, dear headline writers, increased pollution will not turn Drosera rotundifolia into a vegetarian. It may, however, given this work and that before it, be the cause of changing priorities in nitrogen uptake from primarily prey-derived to primarily root-derived. It should be noted, however, that the authors did not set out to assess prey capture rates in these areas, so any statement has to be carefully worded and specifically related to nitrogen assimilation from different sources. We don't know if the plants in areas with more nitrogen capture fewer arthropods. It's entirely possible that the plants that incorporate more nitrogen from their roots capture the same number of prey but preferentially assimilate the nitrogen from the roots.

More troubling, however, is that with increased nitrogen availability in these once off-limits landscapes, opportunistic species may find it easier to overcrowd the poor little perennial carnivorous herbs. (Of course, the increase in nitrogen in this study was not very large and probably would not be enough to allow non-bog-adapted species to thrive.) Most carnivorous plants are low to the ground and depend on high light conditions to thrive; if shaded too much, they may soon succumb to succession. Of course this is only a hypothesis and needs to be studied! I wonder what the headline writers will say then...


References

Millett, J., Svensson, B., Newton, J., & Rydin, H. (2012). Reliance on prey-derived nitrogen by the carnivorous plant Drosera rotundifolia decreases with increasing nitrogen deposition New Phytologist, 195 (1), 182-188 DOI: 10.1111/j.1469-8137.2012.04139.x

Thoren, L., Tuomi, J., Kamarainen, T., & Laine, K. (2003). Resource availability affects investment in carnivory in Drosera rotundifolia New Phytologist, 159 (2), 507-511 DOI: 10.1046/j.1469-8137.2003.00816.x

10 June 2012

A sundew makes a hasty retreat


I'm not yet ready to send out the heralds and call this a success on my first go at cultivating tuberous sundews, but I'm closer now than I was before. If you recall, I originally purchased a lovely specimen of Drosera peltata from California Carnivores in January 2012 and first posted about it in March. It started out as a cute little rosette of carnivorous leaves, then bolted to produce two lovely 6-inch tall stems bearing those irresistible peltate leaves. And then throughout the last few months it was happily going about the business of, well, what sundews do best: capturing prey to collect nutrients.

Most of the tuberous sundews are native to Australia where the winter is rainy and the summer is hot and dry as a bone. This lineage of sundews has evolved the handy adaptation of giving up trying to survive as a full-fledged leafy herb during that hot, dry, unforgiving summer. Instead, they retreat into the soil, packing up their nutrients into root structures called tubers, not unlike a potato in many ways though much smaller.

In just the last few weeks as we approach the hottest late May and early June weather in the Northern Hemisphere here in Ohio, this particular specimen I had was finally ready to make its scheduled retreat. The leaves and stem quickly browned from the tips in a matter of days, my cue to stop watering and let the soil go bone dry lest the tubers succumb to rot as they form. And then, a few weeks later, out of curiosity and because I knew the soil surface in the pot was much too hard for the new growth to break through next year, I dug through the soil to find the tiny tubers:


Those little cream-colored pearls are definitely not perlite! A closer look:


In the above photo, the two tubers toward the top were still attached to the root, the dark brown object leading from center to the bottom right. It was a bumper crop! After sifting through the remainder of the soil, I found ten tubers in all:


The next challenge will be keeping them in a nice, dark place until next fall when they begin to stir. I think the hardest part will be remembering that I have them stuffed away somewhere!

And also, thanks to my friends at Botanical Oddities, I now have tubers from Drosera auriculata. Thanks, guys! Here's hoping I have success with both as I imagine the difficulties of growing tuberous sundews arise when preparing the new soil mix - the sand can't be too sharp or the new growth will be torn up on its several inch ascent from below. It will, at least, be a fun challenge.

17 April 2012

Drosera peltata bit off more than it could chew



I found this grisly scene out in the greenhouse when I got home today. It looks like my Drosera peltata got a little overzealous, trapping this fly (ID? I'm hopeless at identifying anything with legs) by the head. It's at the end of this tuberous sundew's growing season, so all of that energy derived from this meal will be going directly to the tuber that should be forming several centimeters below the soil.

Drosera - Reach out and touch someone grab someone by the head.