The Fanged Pitcher Plant of Borneo

As mammals, and even more so as apes, we tend to associate fangs with threats. The image of two dagger-like teeth can send chills up ones spine. Perhaps it is fitting then that a carnivorous plant from a southeast Asian island would sport a pair of ominous fangs. Friends, I present to you the bizarre fanged pitcher plant (Nepenthes bicalcarata).

This ominous-looking species is endemic to Borneo and gets its common name from the pair of "fangs" that grow from the lid, just above the mouth of the pitcher. Looks aren't the only unique feature of this species though. Indeed, the entire ecology of the fanged pitcher plant is fascinatingly complex.

Lets tackle the obvious question first. What is up with those fangs? There has been a lot of debate among botanists as to what function they might serve. Some have posited the idea that they may deter mammals from feeding on pitcher contents. Others see them as mere artifacts of development and attribute no function to them whatsoever.

In reality they are involved in capturing insects. The fangs bear disproportionately large nectaries that lure prey into a precarious position just above the mouth of the pitcher. Strangely enough, this may have evolved to compensate for the fact that the inside of the pitchers are not very slippery. Whereas other pitcher plant species rely on waxy walls to make sure prey can't escape, the fanged pitcher plant has relatively little waxy surface area within its pitchers. What's more, the pitchers are not very effective at capturing prey unless they have been wetted by rain. The fluid within the pitchers also differs from other Nepenthes in that it is not very acidic, contains few digestive enzymes, and isn't very viscous. Why?

Worker ants cleaning the pitcher (left) and an ant brood chamber inside of the pitcher tendril (right).

Worker ants cleaning the pitcher (left) and an ant brood chamber inside of the pitcher tendril (right).

The answer lies with a specific species of ant. The fanged pitcher plant is the sole host of a carpenter ant known scientifically as Camponotus schmitzi. The tendrils that hold the pitchers themselves are hollow and serve as nest sites for these ants. Ant colonies take up residence in the tendrils and will hunt along the insides of the pitchers. In fact, they literally go swimming in the pitcher fluid to find their meals!

This is why the pitcher fluid differs so drastically from other Nepenthes. The fanged pitcher plant actually does very little of its own digestion. Instead, it relies on the resident ant colony to subdue and breakdown large prey. As a payment for offering the ants room and board, the ants help the plant feed via the breakdown of captured insects (which are often disposed of in the pitchers) and the deposition of nitrogen-rich feces. Indeed, plants without a resident ant colony are found to be significantly smaller and produce fewer pitchers than those with ants. The ants also protect and clean the plant, removing fungi and hungry insect pests.

Sadly, like many other species of Nepenthes, over-harvesting for the horticultural trade as well as habitat destruction have caused a decline in numbers in the wild. With species like this it is so important to make sure you are buying nursery grown specimens. Never buy a wild collected plant! Also, if you are lucky enough to grow these plants, propagate them! Only by reducing the demand for wild specimens can we hope of curbing at least some of the poaching threats. Also, what better way to get your friends into gardening than by sharing with them amazing carnivores like the fanged pitcher plant.

Female flowers

Female flowers

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

Orchid Ant Farms

I am beginning to think that there is no strategy for survival that is off-limits to the orchid family. Yes, as you may have figured out by now, I am a bit obsessed with these plants. Can you really blame me though? Take for instance Schomburgkia tibicinis (though you may also see it listed under the genera Laelia or more accurately, Myrmecophila). These North, Central, and South American orchids are more commonly referred to as cow-horn orchids because they possess hollow pseudobulbs that have been said to been used by children as toy horns. What is the point of these hollow pseudobulbs?

A paper published back in 1989 in the American Journal of Botany found the answer to that question. As it turns out, ants are quite closely associated with orchids in this genus. They crawl all over the flowers, feeding on nectar. The relationship goes much deeper though. If you were to cut open one of these hollow pseudobulbs, you would find ant colonies living within them. The ants nest inside and often pile up great stores of food and eventually waste within these chambers. The walls of the chambers are lined with a dark tissue that was suspect to researchers.

Using radioactively labeled ants, the researchers found that the orchids were actually taking up nutrients from the ant middens! What's more, nutrients weren't found solely in adjacent tissues but also far away, in the actively growing parts of the roots. These orchids are not only absorbing nutrients from the ants but also translocating it to growing tissues.

While orchids without a resident ant colony seem to do okay, it is believed that orchids with a resident ant colony do ever so slightly better. This makes sense. These orchids grow as epiphytes on trees, a niche that is not high in nutrients. Any additional sources of nutrients these plants can get will undoubtedly aid in their long-term survival. Also, because the ants use the orchids as a food source and a nest site, they are likely defending them from herbivores.

Photo Credit: Scott.Zona (http://bit.ly/1hvWiGX)

Further Reading:
http://www.jstor.org/stable/2444355

When a Mutualism Becomes Obligate

Mutualism. The word invokes this warm and fuzzy "you scratch my back and I'll scratch yours" feeling. It is easy to grasp how a mutualism would develop and be maintained. But, in any system, there are bound to be cheaters. Cheaters reduce the fitness of one of the partners so to avoid such things, some species up the ante by resorting to some interestingly "sinister" methods.

Acacias and ants have quite the relationship. Acacias protect themselves by offering ants hollow spines and branches where their colonies can live. They even sweeten the deal via extrafloral nectaries. These are glands on the stems that secrete nectar that the ants eat. In some ant species, this is their only source of food. Needless to say, the ants become highly protective of their acacia trees. They readily attack herbivores and even go as far as to prune away vegetation that may interfere with their host. This seems like a pretty straight forward mutualistic relationship, right?

Ah, but it goes deeper. To make sure that the ants will solely rely on the acacia and are thus completely tied up in the well being of their host, the acacia alters the ants phenotype at birth. Normally these ants have no issues digesting sucrose. Researchers found that the nectar in the extrafloral nectaries contains a protein called "chitinase." Chitinase inhibits the ability of the ants to digest sucrose. When ant eggs hatch into larvae, their first meal is nectar from the extra floral nectaries. Once the larvae ingest this protein they are no longer able to feed on anything other than their hosts nectar. Thus their very survival is completely tied to the Acacia.

I am positive that more examples of such obligate mutualisms abound in nature. We only have to ask the right questions to discover them. It is also interesting considering what we are finding out about our own behavior and how it relates to the microbiome living on and within us. What about human behavior could be described in the context of a relationship similar to ants and acacias?

Photo Credit: Tony Rodd

Further Reading:
http://www.ncbi.nlm.nih.gov/pubmed/24188323

Invasive Ants Destroy Plant Sex Lives

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For all of the amazing symbioses ants and plants share, there is one thing ants seem to get in the way of... plant sex. That's right, plants have found a use for ants in pretty much every way except for when it comes to reproduction (with some exceptions of course). Ants being what they are, they can easily become a force to be reckoned with. For this reason, many plant species have co-opted ants as defense agents, luring them in with nectar-releasing glands, a resource that ants guard quite heavily. 

When it comes to flowering, however, ants can become a bit overbearing. Research done at the University of Toronto shows that the invasive European fire ant has a tendency to guard floral nectar so heavily that they chase away pollinators. By observing fire ants and bumblebees, they found that ants change bumblebee foraging behaviors. The fire ants often harassed and attacked bumblebees as they visited flowers, causing them to spend significantly less time at each flower, a fact that could very well result in reduced pollination for the plant in question. 

This reduction in pollination is made even more apparent for dioecious plants. Since ants are after nectar and not pollen, male flowers received more bumblebee visits than nectar-producing female flowers. This could become quite damaging in regions with heavy fire ant infestations. 

As it turns out, the ants don't even need to be present to ward off bumblebees. The mere scent of ants was enough to cause bumblebees to avoid flowers. They apparently associated the ant smell with being harassed and are more likely to not chance a visit. Of course, this study was performed on using an invasive ant species. Because so many plant species recruit ants for things like protection and seed dispersal, it is likely that under natural conditions, the benefit of associating with ants far outweighs any costs to reproductive fitness. More work is needed to see if other ant specie exhibit such aggressive behavior towards pollinators. 

Photo Credit: Lalithamba (https://www.flickr.com/people/45835639@N04)

Further Reading:

 http://www.researchgate.net/profile/James_Thomson13/publication/259319739_Ants_and_Ant_Scent_Reduce_Bumblebee_Pollination_of_Artificial_Flowers/links/554b8fd90cf21ed213595eff.pdf

A Real Cliffhanger

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Cliff faces are some of the most interesting habitat types on the planet. Few places in the world are as inhospitable. They are low in nutrient levels, they have limited space for root growth, and offer very little for recruitment. Cliffs do offer some benefits though. They are often sheltered from extremes in climate and can be inaccessible to large herbivores. With that in mind, it is understandable how they can be a haven for some very unique and equally extreme life forms.

One such life form that comes to mind is Borderea chouardii. This strange plant grows only on a couple cliff faces in the Pyrenees mountain range in Spain. It is critically endangered as it represents a relict population of a once tropical Tertiary environment. What makes it more interesting is the double mutualism it has formed with ants. As we have touched on a few times in the past, ants are often recruited as seed dispersers. Borderea chouardii does just that. In many of the observed cases of seed dispersal, researchers found that ants were the culprit. Interestingly enough, a majority of the remaining cases were due to the plant literally planting its own seeds. Known as "skototropism," the stems of the seed cases grow into dark crevices, which are perfect spots for seed to germinate and grow. Surprisingly, gravity plays a very small role in the reproduction of this species.

Let me back up for a bit here. I did mention this plant has a double mutualism with ant species after all. Based on years of observation, researchers found that ants actually served as the most efficient pollinator for Borderea chouardii. This is not a common thing. Generally speaking, ants do not make for effective pollinators. Most species have glands that secrete substances that destroy pollen. However, in a mountainous cliff setting, winged insects are relatively rare, so Borderea chouardii and ants have evolved together into this oddball double mutualism. To add an extra layer of complexity to the system, dare I mention that it isn't just one ant species that Borderea chouardii relies on, but rather 3. Two ant species serve as the pollinators while a a third ant species serves as a seed disperser. This is one risky plant species. The plant gets around the rarity of successful recruitment by living a long time. Individual plants can live upwards of 300 years, which is quite possibly the record for a non-clonal forb species.

Photo Credit: María B. García, Xavier Espadaler, Jens M. Olesen

Further Reading:

http://www.plosone.org/…/info%3Adoi%2F10.1371%2Fjournal.pon…

http://www.iucnredlist.org/details/162110/0

Tillandsias and Ants

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Tillandsias are all the rage. Their relative ease of care has found them included in seemingly every terrarium sold these days - often in very inappropriate circumstances that result in their death. There is no denying that these epiphytic relatives of the pineapple are unique and beautiful plants but I would argue that their ecology is probably the coolest aspect about them. I am particularly fond of the bulbous species because of their relationship with ants. 

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That's right, there are upwards of 13 species of bulbous Tillandsia that offer up housing for ants. If you look closely at the leaves of these species, you will notice that they roll up to form tubes that lead down into the bulb. The space between the leaves is a hollow chamber, a perfect microclimate for ants to nest. In many habitats, the Tillandsia offer better housing than the surrounding environment. One would be surprised at how many ants can fit in there too. Colonies containing anywhere between 100 - 300 individuals are not unheard of. 

The rewards for the plant are obvious. Ants provide nutrients as well as protection. In return the ants get a relatively safe and dry place to live. Ant houses have been recorded in roughly 13 different species, many of which are some of the most commonly sold Tillandsias on the market like T. baileyi, T. balbisiana, T. bulbosa, and T. caput-medusae. If this doesn't make your hanging glass Tillandsia orb even cooler then I don't know what will.

Photo Credits: scott.zona (http://bit.ly/16kZ1RR) and Alex Popovkin (http://bit.ly/1BXMEUH)

Further Reading:

http://www.jstor.org/stable/2483400?seq=1#page_scan_tab_contents

http://www.geraceresearchcentre.com/pdfs/2ndBotany/7_Eshbaugh_2ndBotany.pdf