The Carnivorous Waterwheel

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Bladderworts (Utricularia spp.) aren't the only carnivorous plants stalking prey below the water surface. Meet the waterwheel (Aldrovanda vesiculosa). At first glance it looks rather unassuming but closer inspection will reveal that this carnivore is well equipped for capturing unsuspecting prey. 

The waterwheel never bothers with roots. Instead, it lives out its life as a free floating sprig, its stem it covered in whorls of filamentous leaves, each tipped with a tiny trap. The trapping mechanism is a bit different from its bladderwort neighbors. Instead of bladders, the waterwheel produces snap traps that closely resemble those of the Venus fly trap (Dionaea muscipula). These traps function in a similar way. When zooplankton or even a small fish trigger the bristles along the rim, the trap snaps shut and begins the digestion process.

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This similarity to the Venus fly trap is more than superficial. DNA analysis reveals that they are in fact close cousins. Together with the sundews, these plants make up the family Droseraceae. The evolutionary history of this clade is a bit confusing thanks to a limited fossil record. Today, the waterwheel is the only extant member of the genus Aldrovanda but fossilized seeds and pollen reveal that this group was once a bit more diverse during the Eocene. Whenever these genera diverged, it happened a long time ago and little evidence of it remains.

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At one point in time, the waterwheel could be found growing in wetland habitats throughout Africa, Europe, Asia, and even Australia. Today it is considered at risk of extinction. Its numbers have been severely reduced thanks to wetland degradation and destruction. Of the 379 known historical populations, only about 50 remain in tact today and many of these are in rough shape. Agricultural and industrial runoff are exacting a significant toll on its long term survival. To make matters worse, sexual reproduction in the waterwheel is a rare event. Most often this plant reproduces vegetatively, reducing genetic diversity. What's more, natural dispersal into new habitats is extremely limited. 

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Oddly enough, populations of this plant have popped up in a few locations in eastern North America. These introductions were not a mistake either. Carnivorous plant enthusiasts concerned with the plight of this species in its native habitat began introducing it into water ways in New Jersey, New York, and Virginia where it is now established. Oddly enough, these introductions have performed far better than any of the reintroduction attempts made in its native range in Europe. Of course, this is always cause for concern. Endangered or not, the introduction of a species into new habitat is always risky. Still, there is hope yet for this species. Its popularity among plant growers has led to an increase in numbers in cultivation. At least folks have learned how to cultivate it until more comprehensive and effective conservation measures can be put into place. 

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3] [4] [5]

Genetic Origins of Carnivory in the Venus Fly Trap

Our fascination with the Venus fly trap (Dionaea muscipula) is undeniable. What's not to love about a plant that eats animals? Our obsession with this species has led to a long history of investigation (as well as deplorable practices like poaching). However, despite our familiarity with the Venus fly trap, we still have much to learn about its biology. For instance, little is known about the origins of the molecular machinery involved in its carnivorous lifestyle. Thanks to a 2016 paper published in Genome Research, we now have some insights.

As you can probably imagine, the Venus fly trap genome has been of interest to science for quite some time. After all, it is likely to harbor the keys to this carnivorous curiosity. However, despite looking, no carnivory-specific genes have ever been found. It's as if this wonder of evolution has no genetic basis. Of course, things are not that simple. A breakthrough was made when a team of researchers based out of Germany and Saudi Arabia decided to take a look at "transcription profiles." Essentially, these are chemical indicators of gene activity. When a gene is activated, it produces a chemical signal that can be easily traced. In doing so, researchers are able to get a clear picture of what is going on at a molecular level when an organism responds to its environment. 

What the team discovered is pretty amazing. Instead of a new family of carnivorous genes coming online, they found that the Venus fly trap has retooled a handful of genes that are used by many different plant species for defense. As it turns out, the Venus fly trap has coopted a set of genes that in most plants are activated when the plant becomes damaged. When the traps were stimulated by the insects stuck inside, transcripts for the production of chitinase, which is basically a insect digesting enzyme, became amplified. For non-carnivorous plants, chitinase is usually produced in response to insect attack or fungal infection and is believed to be a defense mechanism. This was not the only gene activity either. When an insect was trapped by the plant, transcripts for jasmonic acid saw an increase. Also, when digestive glands within the trap began to activate, the genes responsible for this were showing an expression pattern akin to that of nutrient transport in roots. 

It would seem that the evolution of carnivory in this species did not involve novel genes. Instead, the evolution of the Venus fly traps carnivorous lifestyle involved a reprogramming of sets of genes common to most plant species. In essence, the Venus fly trap has melted its shield to build a sword, only the sword is a trap of exquisite beauty and effectiveness. 

Photo Credit: Scott Schiller

Further Reading:

http://bit.ly/1UL5RHc

The Plight of the Venus Fly Trap

The fact that endangered plants do not receive the same protection as animals speaks volumes towards our perception of their importance. If one were to gun down an endangered bird, regardless of where it happened, they would likely face jail time. This is a good thing. However, regardless of how endangered a plant may be, as long as it is on private property and written consent is given by the land owner, one can harvest to their hearts content. It could be the last population in existence. The point of the matter is, endangered plants only receive protection on federal lands. Even then, enforcement is difficult at best. 

Plant poaching is serious business. The victims are usually pretty species like orchids or valuable species like American ginseng. The rarer something is, the higher the price. Someone will always be willing to pay top dollar to add something rare to their collection. This story is repeated time and time again throughout the world but one particularly interesting example centers on a plant that most people are familiar with and have probably attempted to grow at one point in their lives - the Venus fly trap (Dionaea muscipula).

It may be counter intuitive to believe that a plant so often sold in grocery stores could be in trouble but the Venus flytrap truly is. In the wild, Venus fly traps are what we call endemics. They are native to a small portion of land in the Carolinas and nowhere else. Sadly, the long leaf pine savannahs and Carolina bays that they call home are being gobbled up by golf courses, pine plantations, and housing developments. The Venus fly trap (as well as over 100 other endangered species) are quickly losing the only habitat in the world that they exist. 

Of the 107 Venus fly trap populations that remain, only 65 of them are located on protected land. If habitat destruction wasn't enough, plant collectors, both legal and illegal, descend upon this region to get their hands on wild fly traps. This, my friends, is the definition of stupidity and greed. A simple internet search will turn up countless hobbyists and nurseries alike that culture these plants in captivity. It isn't very hard to do and it can be done on a massive scale. 

There is simply no reason to have to harvest Venus fly traps from the wild. None. Despite the plight of this unique species, legal protection of the Venus fly trap is almost non existent. It is listed as a "species of special concern" in North Carolina, which basically means nothing. For poachers, this really doesn't matter. Thousands of plants are stolen from the wild on protected and unprotected lands alike. Recent felony charges against Venus fly trap poachers offer some hope that the situation may be changing but that still does nothing to protect plants that, through senseless loopholes, are collected legally. 

This circles back to those plants we often see for sale in grocery stores. If they are in a red pot with a clear plastic cup on top, you can almost guarantee they came from the Fly-Trap Farm. This company openly admits to buying and selling plants collected from the wild. Despite the afore mentioned fact that culturing them in captivity is done with relative ease, the demand for these carnivorous curiosities coupled with their perceived disposability means that wild populations of this already threatened plant are growing smaller and smaller. 

Venus fly traps are endemics. They grow nowhere else in the world. If their habitat is destroyed and demand for wild plants continues, there is no Plan B. This species will be lost to the world forever. Again, there is no reason to buy wild collected plants. Plenty of hobbyists and nurseries such as The Carnivore Girl, Meadowview Biological Research Station, and California Carnivores (just to name a few) offer reasonably priced cultivated Venus fly traps. Whereas it is difficult or even impossible to squash poaching for good, we as consumers can always vote with our wallets. 

It is tough to say whether or not there is hope for the Venus fly trap and its neighbors. This region of the Carolinas is growing in its human population. So many Venus fly trap populations have already been lost forever and more are likely to disappear in the near future. There may be hope, however, and it comes in the form of land protection. Recent acquisitions of large tracts of Venus fly trap habitat are promising. Regardless, unless the public speaks up about the plight of these long leaf pine savannahs and Carolina bays, no one is going to listen. Plants deserve the same protection as animals. Heck, we wouldn't have any cute and fuzzy megafauna if it were not for healthy plant populations. Protecting plants needs to be a priority. 

Photo Credit: NC Orchid (http://bit.ly/1MUlE0x)

Further Reading:
http://archive.audubonmagazine.org/features0803/carnivorousplants.html

http://www.iucnredlist.org/details/39636/0

http://wunc.org/post/north-carolina-enacts-venus-flytrap-theft-laws-how-big-problem-really#stream/0