A New Look at a Common Bladderwort

February 26, 2015

Photo by Kevin Thiele licensed under CC BY 2.0

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.

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)

An Abominable Mystery

February 5, 2015

Photo by Shizhao licensed under CC BY-SA 2.5

We all love flowers but for all the attention we pay them, their origin remains elusive. Darwin called their sudden appearance in the fossil record an “abominable mystery.” Since Darwin's time, we have been able to clarify that picture a little bit. Even so, our understanding of the origin of the angiosperm lineage is dubious at best. When and why did flowers evolve?

For millions of years the land was dominated first by ferns and their allies and then by gymnosperms like cycads and gingkos. It was not until the Cretaceous that angiosperms began to rise to their current place as the dominant and most diverse group of plants. Their sudden appearance on the scene has been largely shrouded in mystery. There is scant fossil evidence to illustrate the early evolutionary steps in this development of flowers. Many paleobotanists believed that flowers had their origin in shrub-like ancestors of gymnosperms. Others felt that the origin of flowers belonged with the seed ferns (http://bit.ly/1zKfriM).

Around 2001 a fossil discovery from Yixian Formation, Liaoning, China was believed to have changed all of that. A researcher by the name of Ge Sun had stumbled upon a very primitive looking fossil plant. To his surprise, the reproductive structures seemed to show stamens in pairs below carpels and a lack of petals and sepals. The formation in which the fossil was found dated back to the Jurassic period. Could this represent the remains of the earliest flowers?

The fossil has been coined Archaefructus and since its discovery at least two species have been identified. Archaefructus was an aquatic plant, likely living on the edge of freshwater lakes. These fossils (as one would expect) are quite contentious. Some argue that it is more derived than would be expected from the first flower. Recently it has been suggested that Archaefructus is a sister lineage to early flowering plants, not unlike Nymphaeales or Amborella living today.

What Archaefructus does suggest is that flowers had their origin much earlier than the Cretaceous. Other discoveries from the same formation (ie. Archaeamphora longicervia) suggest that flowering plants were already diversifying at this time. So, if this is the case, when did flowers appear on the scene? Far from the smoking gun that a fossilized flower would represent, researchers are nonetheless finding tantalizing fossil evidence that places the origin of flowering plants all the way back to the Triassic.

By examining Triassic microfossils, some researchers believe they have found fossilized pollen grains that are distinctly angiosperm in origin. I won't go into it here but extant examples show a major distinction between pollen from gymnosperms and pollen from angiosperms. If this is true, flowers may be way older than ever expected. For now, the jury is still out on this one.

Flowers evolved for sex. We associate animals like bees, bats, and birds with flowers today but most of these lineages came much later in the game. Exactly what was around pollinating early flowers remains a bit of a mystery as well. Were the earliest flowers wind pollinated or was there some insect or even reptile that served the selection pressure necessary for their evolution? Only time and more fossil discoveries will tell.

Photo Credit: Shizhao (Wikimedia Commons)

Why All the Lace?

January 26, 2015

All too often, botanizing is restricted to the land. Sure, there is the occasional foray to a marsh or bog but, for the most part, relatively few plant folk like to get wet in their quests to meet new and exciting plant species. There is an entire world of aquatic plants that don't get enough credit. One such plant is Aponogeton madagascariensis, the lace plant.

Anyone into planted aquariums has undoubtedly come across this species at least once. It is kind of a holy grail of aquarium gardening. Hailing from Madagascar, this is one of the truly aquatic Aponogeton species. Though there are a few different geographic variations, they are all easily recognized by the lacy appearance of their leaves. Known as "fenestration," the lacy structure is the result of programmed cell death during the development of the leaves. As interesting as that fact is in and of itself, the question remains, what is the function of fenestration?

There have been many hypotheses put forward to explain this phenomenon. Some believe it helps to reduce damage from turbulence wheras others believe it helps to increase movement around the leaves and helps avoid stagnation. The truth is, no one is entirely certain. However, a clue to the benefits of fenestration has come out of work done on an entirely unrelated terrestrial plant species.

The epiphytic arum commonly referred to as a Swiss cheese plant (Monstera deliciosa) also exhibits fenestrated leaves. Researchers at Indiana University in Bloomington have found that the holes in the leaves may actually help gather more light in a shaded environment. The understory of a rainforest and the underwater habitat in which the lace plant grows may be more similar in light availability than you would think. How would holes in the leaves allow the plant to gather more light?

As it turns out, a fenestrated leaf can grow much larger while still maintaining the same amount of surface area. By spreading out its surface area over a larger region, a fenestrated leaf is actually more efficient at gathering what limited light is available. More work needs to be done to see if this is truly the case for the lace plant but the idea is tantalizing to say the least. Sadly, like too much of Madagascar's wildlife, the lace plant is becoming quite rare in the wild due to habitat destruction. So, the next time you come across one of these in an aquarium store, make sure to give this plant the attention it deserves.

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

Mysterious Marimo

January 22, 2015

I was recently approached by a lady who was quite curious as to what mystical energies could have created the increasingly popular marimo balls that are often seen for sale in aquarium shops. Surely no natural force could create such spherical wonders in nature, right? She seemed quite disappointed by my answer and left feeling cheated of the super natural mechanism she was looking for. However, before we discuss the source of these fury green balls, let's start at the beginning.

Marimo balls or lake balls are a specific growth form of a macroalga known scientifically as Aegagropila linnaei. It belongs to the Cladophoraceae family and can be found in lakes throughout the northern hemisphere. They are most popularly known from lakes in Japan where they hold serious cultural significance. The word "marimo" is Japanese for "ball seaweed."

So, how does this species of alga form itself into a ball? The answer is not mystical, though it is quite specific. To start with, the ball form of this alga is not the only way it grows. Populations will also form as mats on the lake bed, carpeting rocks and other debris. When pieces break off and become free floating, tidal action gently rolls them around. As they grow and move, they become tangled up and gradually form themselves into this spherical shape. The overall shape and survival of the alga in this form is reliant on this tidal motion. All parts of the ball actively photosynthesize and if it is not exposed to light all over, the shaded parts die and the ball will be no longer. Luckily, the alga reproduces vegetatively so the broken parts can still go on living.

Sadly, marimo balls are not doing too well in the wild. As we have seen with so many other species, human impacts are taking their toll on Aegagropila linnaei. Eutrophication, logging, and development within the watersheds that feed these lakes are causing the once clear waters to become quite murky. As this issue increases, the alga can no longer photosynthesize on a level that can sustain its populations. Acid rain is another big issue. Marimo balls tend to grow in calcareous lakes. As the water acidifies, they are unable to cope. Finally, one of the other issues facing the marimo balls is their popularity. In some areas, they are being harvested for the aquarium trade at unsustainable levels. One source claims that a majority of marimo balls for sale in aquarium shops are sourced from the Ukraine, which means that those populations are under serious pressure.

Luckily, their popularity may also lead to more protective measures. For instance, they are so important to Japanese culture that they are now a protected species there. The Netherlands is also waking up to the decline of this species. Until more can be done, it is best to only buy from nursery grown sources. Formation of the balls has been done in an artificial setting. Truly, no species is safe from the irresponsible nature of modern man.

Photo Credit: mossball.com