The Ant-Farming Tillandsias

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.

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 at the base. The space between the leaves forms a hollow chamber, functioning as a perfect microclimate for ants to nest. In many habitats, these 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 ants 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 domatia have been recorded in roughly 13 different species, many of which are some of the most commonly sold Tillandsias on the market such as 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: [1] [2]

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]

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