Bacteria Help the Cobra Lily Subdue Prey

The aptly named cobra lily (Darlingtonia californica) is one of North America's most stunning pitcher plants. Native to a small region between northern California and southwestern Oregon, this bizarrely beautiful carnivore lives out its life in nutrient poor, cold water bogs and seeps. Although it resides in the same family as our other North American pitcher plants, Sarraceniaceae, the cobra lily has a unique taxonomic position as the only member of its genus.

It doesn't take much familiarity with this plant to guess that it is carnivorous. Its highly modified leaves function has superb insect traps. Lured in by the brightly colored, tongue-like protrusions near the front tip of the hood, insects find a sweet surprise. These tongue-like structures secrete nectar. As insects gradually make their way up the tongue, they inevitably find themselves within the downward pointing mouth of the pitcher. This is where those translucent spots on the top of the hood come in.

These translucent spots trick the insects into flying upwards into the light. Instead of a clean getaway, insects crash into the inside of the hood and fall down within the trap. The slippery walls of the pitchers interior make escape nearly impossible but that isn't the only thing keeping insects inside. Research has shown that the cobra lily gets a helping hand from bacteria living within the pitcher fluid.

Unlike other pitcher plants, the cobra lily does not fill its traps with rain water. The downward pointing mouth prevents that from happening. Instead, the pitchers secrete their own fluid by pumping water up from the roots. Although there is evidence that the cobra lily does produce at least some of its own digestive enzymes, it is largely believed that this species relies heavily on a robust microbial community living within its pitchers to do most of the digesting for it. This mutualistic community of microbes save the plant a lot of energy while also providing it with essential nutrients like nitrogen in return for a safe place to live.

That isn't all the bacteria are doing for this pitcher plant either. As it turns out, the pitchers' microbial community may also be helping the plant capture and subdue its prey. A recent study based out of UC Berkeley demonstrated that the presence of these microbes helps lower the surface tension of the water, effectively drowning any insect almost immediately.

The microbes release certain compounds called biosurfactants. Through an interesting chemical/physical process that I won't go into here, this keeps insects from using the surface tension of the water's surface to keep them afloat, not unlike a water strider on a pond. Instead, as soon as insects hit the bacteria infested waters, they break the surface tension and sink down to the bottom of the pitcher where they quickly drown. There is little chance of escape for a hapless insect unlucky enough to fall into a cobra lily trap.

Although plant-microbe interactions are nothing new to science, this example is the first of its kind. Although this prey capture role is very likely a secondary benefit of the microbial community within the pitchers, it very likely makes a big difference for these carnivores living in such nutrient poor conditions.

Photo Credit: Wikimedia Commons

Further Reading: [1]

An Introduction to Cephalotus follicularis - A Strange Carnivore From Australia

In a small corner of western Australia grows one of the most unique carnivorous plants in the world. Commonly referred to as the Albany pitcher plant, Cephalotus follicularis is, evolutionarily speaking, distinct among the pitcher plants. It is entirely unrelated to both the Sarraceniaceae and the Nepenthaceae.

This stunning case of convergent evolution stems from similar ecological limitations. Cephalotus grows in nutrient poor areas and thus must supplement itself with insect prey. It does so by growing modified leaves that are shaped into pitchers. The lid of each pitcher serves two purposes. It keeps rain from diluting the digestive enzymes within and it also confuses insects.

A close inspection of the lid will reveal that it is full of clear spots. These spots function as windows, allowing light to penetrate and confuse insects that have landed on the trap. As they fly upwards into the light, they crash into the lid and, with a little help from physics, fall down into the trap.

The relationship of Cephalotus to other plants has been the object of much scrutiny. Though it is unique enough to warrant its own family (Cephalotaceae), its position in the greater scheme of plant taxonomy originally had it placed in Saxifragales. Genetic analysis has since moved it out of there and now places it within the order Oxalidales. What is most intriguing to me is that the closest sister lineage to this peculiar little pitcher plant are a group of trees in the family Brunelliaceae. Evolution can be funny like that.

Regardless of its relationship to other plants, Cephalotus follicularis has gained quite a bit of attention over the last few years. Its strange appearance and carnivorous habit have earned it a bit of stardom in the horticultural trade. A single specimen can fetch a hefty price tag. As a result, collecting from wild populations has caused a decline in numbers that are already hurting due to habitat destruction. Luckily they are easy to culture in captivity, which will hopefully take pressure off of them in the wild.

What's more, the loss of Cephalotus from the wild is hurting more than just the plant. A species of flightless, ant-mimicking fly requires Cephalotus pitchers to rear its young. They don't seem to mind growing up in the digestive enzymes of the pitchers and to this date, their larvae have been found living nowhere else. If you are lucky enough to grow one of these plants, share the wealth. Captive reared specimens not only take pressure off wild populations, they are also much hardier. Lets keep wild Cephalotus in the wild!

Devil's Claw

Meet Proboscidea louisianica aka the Devil's claw plant. The common name comes from the nasty looking seed pods that evolved in response to large mammals that once roamed this continent. The genus Proboscidea has traditionally been placed into the sesame family (Pedaliaceae) due to superficial similarities in flower and seed morphology, but more recent work has moved it into the unicorn plant family, Martyniaceae. That's right... unicorn plants.

The entire family is found in the New World, with P. lousianica hailing from arid parts of the southern portions of North America. There are some aspects of this species that make them quite interesting to botanists. For starters, the apt name of Devil's claw was bestowed upon this genus because of the bizarre seed pods they produce. Similar to burs, they can become entangled in fur quite readily. The odd thing about this seed dispersal mechanism for P. louisanica is how big the seed pods are. Until cattle were introduced to this continent, animals large enough to effectively disperse these massive seed pods seemed to be missing, having gone extinct at the end of the last ice age. It is believed that this plant may be an anachronism of this era.

The flora we are familiar with today spent millennia co-evolving with ice age megafauna like mammoths and giant ground sloths. There is a growing school of thought that many close relationships probably developed over this time and have not yet been lost due to the relatively limited amount of time since the extinction of these large mammals. There are some people who will tell you that the seed pods are "designed" to ensnare small mammals like mice, causing them to die, which then provides the seeds a nutrient-rich, rotting corpses on which to germinate. I have never been able to find any evidence in support of these claims.

Another intriguing anatomical feature of this species are the countless sticky glands that cover the entire plant. These readily ensnare insects that land on or try to climb up the plant. Analysis of the fluids secreted by these glands show evidence of digestive enzymes but the jury still seems to be out on whether or not P. louisanica is undergoing any active carnivorous behavior.

It is more likely that these glands are a form of defense against insect herbivores and indeed they work quite well. Even a brief run-in with this plant leaves you quite sticky and slimy. It is possible that by ensnaring herbivorous insects, the plant can attract carnivorous insects that will eat the herbivores and then "repay" the devil's claw with nutrient-rich feces. Another possibility is that the glands cause the plant to become covered in sand grains over time. Such sandy armor would get in the way of hungry herbivores. To ad insult to injury, the plant kind of smells. It has been likened to old gym clothes. .

This is a neat plant. I have had fun growing them in the past. They are an annual but may reseed if care is not taken to removing the seed pods before they pop open. Because of their lively appearance and the unique look of their seed pods, these plants are often grown as horticultural oddities. Be careful though, as they have escaped cultivation outside of their native range and can be considered a noxious weed!

Photo Credit: John Loo

Further Reading: [1] [2] [3] [4]

A New Look at a Common Bladderwort

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It is so often that common species are overshadowed by something more exotic. Indeed, we know more about some of the rarest plants on earth than we do about species growing in our own back yards. Every once in a while researchers break this pattern and sometimes this yields some amazing results. Nowhere has this been better illustrated in recent years than on the humped bladderwort, Utricularia gibba. 

This wonderful little carnivore can be found growing in shallow waters all over the world. Like all Utricularia, it uses tiny little bladders to capture its even tinier prey. Despite its diminutive size, U. gibba is nonetheless a very derived species. For all of its wonderful physical attributes, the real adventure begins at the microscopic level. As it turns out, U. gibba has some amazing genetic attributes that are shining light on some incredible evolutionary mechanisms. 

When researchers from the University at Buffalo, Universitat de Barcelona in Spain, and LANGEBIO in Mexico decided to sequence the genome of this plant, what they found was quite startling. For a rather complex little plant, the genome of U. gibba is incredibly small. What the researchers found is that U. gibba appears to be very efficient with its DNA. Let's back up for a moment and consider this fact. 

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The genomes of most multicellular organisms contain both coding and non-coding DNA. For decades researchers have gone back and forth on how important non-coding DNA is. They do not code for any protein sequences but they may play a role in things like transcription and translation. For a long time this non-coding DNA has been referred to as junk DNA. 

This is where things get interesting. Sequencing of the U. gibba genome revealed that only 3% of its genome consisted of non-coding or junk DNA. For some reason the U. gibba lineage has managed to delete most of it. To put things in perspective, the human genome is comprised of roughly 98% non-coding or junk DNA. Despite its rather small and efficient genome, U. gibba nonetheless has more genes than plants with larger genomes. This may seem confusing but think of it this way, whereas U. gibba has a smaller overall genetic code, it is comprised of more genes that code for things like digestive enzymes (needed for digesting prey) and cell walls (needed to keep water out) than plants with more overall genetic code such as grapes or Arabidopsis. 

As one author put it, this tiny ubiquitous plant has revealed "a jewel box full of evolutionary treasures." It is a species many of us have encountered time and again at the local fishing hole or in your favorite swimming pond. Time and again we pass by the obvious. We overlook those organisms that are most familiar to us. We do so at the cost of so much knowledge. It would seem that the proverbial "Old Dog" has plenty of tricks to teach us. 

Photo Credit: Kevin Thiele (http://bit.ly/1Flouqd) and Reinaldo Aguilar (http://bit.ly/1B6mnHN)

Further Reading:

http://www.nature.com/nature/journal/v498/n7452/full/nature12132.html

http://mbe.oxfordjournals.org/content/early/2015/01/31/molbev.msv020

http://plants.usda.gov/core/profile?symbol=UTGI

Slippery When Wet

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Pitcher plants in the genus Nepenthes have been getting a lot of attention in the literature as of late. Not only have researchers discovered the use of ultraviolet pigments around the rims of their pitchers, it has also been noted that the pitchers of many species aren't as slippery as we think they are. Indeed, scientists have noted that prey capture is at its highest only when the pitchers are wet. This seems counterintuitive. Why would a plant species that relies on the digestion of insects for most of its nitrogen and phosphorus needs produce insect traps that are only effective at certain times? After all, it takes a lot of energy for these plants to produce pitchers, which give little to nothing back in the way of photosynthesis. 

The answer to this peculiar conundrum may lie in the types of insects these plants are capturing. Ants are ubiquitous throughout the world. Their gregarious and exploratory nature has provided ample selection pressures for much of the plant kingdom. They are particularly well known for their military-esque raiding parties. It is this behavior that researchers have looked at in order to explain the intermittent effectiveness of Nepenthes pitchers. 

A recent study that looked at Nepenthes rafflesiana found that ants made up 65% of the prey captured, especially on pitchers produced up in the canopy. What's more, younger pitchers produced closer to the ground were found to be much more slippery (containing more waxy cells) than those produced farther up on the plant. When the pitchers of this species were kept wet, prey capture consisted mostly of individual insects such as flies. However, when allowed to dry between wettings, the researchers found that prey capture, specifically ants, increased dramatically. How is this possible?

It all goes back to the way in which ants forage. A colony sends out scouts in all directions. Once a scout finds food, it lays down a pheromone trail that other ants will follow. It is believed that this is the very behavior that Nepenthes are relying on. The traps produce nectar as a lure for their insect prey. As the traps dry up, the nectar becomes concentrated. Ants find this sugary treat irresistible. However, if the pitcher were to be slippery at all times, it is likely that most ant scouts would be killed before they could ever report back to the colony. By reducing the slippery waxes, especially around the rim of the trap, the Nepenthes are giving the ants a chance to "spread the news" about this new food source. Because these plants grow in tropical regions, humidity and precipitation can fluctuate wildly throughout a 24 hour period. If the scouting party returns at a time in which the pitchers are wet then the plant stands to capture far more ants than it did if it had only caught the scout. 

This is what is referred to as batch capture. The plants may be hedging their bets towards occasional higher nutrient input than constant low input. This is bolstered by the differences between pitchers produced at different points on the plant. Lower pitchers, especially on younger plants are far more waxy and thus are constantly slippery. This allows constant prey capture to fuel rapid growth into the canopy. Upper pitchers on older individuals want to maximize their yields via this batch capture method and therefore produce fewer waxy cells, relying on a humid climate to do the work for them. It is likely that this is a form of tradeoff which benefits different life cycle stages for the plant. 

Photo Credit: Andrea Schieber (http://bit.ly/1xUsGJk)

Further Reading:

http://rspb.royalsocietypublishing.org/content/282/1801/20142675