Growing Camouflage

A garden on the back of a weevil living a humid Chilean rainforest.

A garden on the back of a weevil living a humid Chilean rainforest.

Lots of us will be familiar with organisms like decorator crabs that utilize bits and pieces of their environment, especially living sea anemones, as a form of camouflage and protection. Examples of terrestrial insects attaching bits and pieces of lichens to their body are not unheard of either. However, there are at least two groups of arthropods that take their camouflage to a whole new level by actively growing miniature gardens on their bodies.

Little is known about these garden-growing arthropods. To date, these miniature gardens have only been reported on a few species of weevil in the genus Gymnopholus as well as a species of millipede called Psammodesmus bryophorus. Coined epizoic symbiosis, it is thought that these gardens serve as a form of protection by camouflaging the gardeners against the backdrop of their environment.

Bryophytes on a  Psammodesmus bryophorus  male.

Bryophytes on a Psammodesmus bryophorus male.

Indeed, both groups of arthropods frequent exposed areas. What is most remarkable about this relationship is that these plants were not placed on the carapace from elsewhere in the environment. Instead, they have been actively growing there from the beginning. Closer inspection of the cuticle of these arthropods reveals unique structural adaptations like pits and hairs that provide favorable microclimates for spores to germinate and grow.

The plant communities largely consist of mosses and liverworts. At least 5 different liverwort families are represented and at least one family of moss. Even more remarkable is the fact that even these small botanical communities are enough to support a miniature ecosystem of their own. Researchers have found numerous algae such as diatoms, lichens, and a variety of fungi growing amidst the mosses and liverworts. These in turn support small communities of mites. It appears that an entire unknown ecosystem lives on the backs of these mysterious arthropods.

FIGURE 39. Elytral base of Gymnopholus (Niphetoscapha) nitidus with exudates. FIGURES 40a–b. Gymnopholus (Niphetoscapha) inexspectatus sp. n., live specimen with incrustrations of algae and lichens; photographs M. Wild, Mokndoma.  [SOURCE]

FIGURE 39. Elytral base of Gymnopholus (Niphetoscapha) nitidus with exudates. FIGURES 40a–b. Gymnopholus (Niphetoscapha) inexspectatus sp. n., live specimen with incrustrations of algae and lichens; photographs M. Wild, Mokndoma. [SOURCE]

There is still much to be learned about this symbiotic relationship. Although camouflage is the leading hypothesis, no work has been done to actually investigate the benefits these arthropods receive from actively growing these miniature gardens on their backs. Mysteries still abound. For instance, in the case of the millipede, gardens are found more frequently on the backs of males than on the backs of females. Could it be that males spend more time searching their environment and thus benefit from the added camouflage? Only further research will tell.

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

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

Meet The Ghostworts

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I love parasitic plants and I love liverworts. Imagine my excitement then when I learned that there are at least two species of parasitic liverworts! These bizarre little plants are currently the only parasitic non-vascular plants known to science. 

The first description of a ghostwort dates back to 1919. Although no description of habitat was given, the account describes a set of liverwort thalli containing no chlorophyll and whose cells were full of mycorrhizal fungi. They were assigned to the genus Aneura and that was that. Further descriptions of this plant would not be made for more than a decade.

A ghostwort gametophyte with spike-like sporophytes.

A ghostwort gametophyte with spike-like sporophytes.

Proper attention was not given to this group until the 1930's. More plants started turning up among the humus and mosses of forests and wetlands throughout Finland, Sweden, and Scotland. A more thorough workover of specimens was made and the plants were moved into their own genus, Cryptothallus, which accurately captured their subterranean habit. They were given the name Cryptothallus mirabilis.

Another species of Cryptothallus was discovered in Costa Rica in 1977. It was named Cryptothallus hirsutus. Only one other collection of these species was made and it remains the lesser known of the two species. It is interesting to note the disparity between their ranges, with C. mirabilis inhabiting northern portions of Europe, and C. hirsutus only known from those two collections in Central America. Regardless, these odd liverworts have received a bit more attention in recent years.

It seems that the ghostworts manage to capture the attention of anyone who looks hard enough. For instance, a handful of attempts have been made to cultivate ghostworts in a controlled lab setting. Originally, plants were grown exposed to varying levels of light but try as the may, researchers were never able to coax the plants into producing chlorophyll. It would appear that these tiny liverworts are in fact some sort of parasite.

Spike-like sporophytes with a branching gametophyte. 

Spike-like sporophytes with a branching gametophyte. 

Proper evidence of their parasitic lifestyle was finally demonstrated 2003. Researchers were able to grow C. mirabilis in specialized observation chambers in order to understand what is going on under the soil. As it turns out, those numerous mycorrhizal connections mentioned in the original description are the key to survival for the ghostworts. The team showed that the ghostwort tricks fungi in the genus Tulasnella into forming mycorrhizal connections with its cells. These fungi also happen to be hooked up to a vast network of pine and birch tree roots.

By tricking the fungi, into an association, the ghostworts are able to steal carbohydrates that the fungi gain from the surrounding trees. Like all mycoheterotrophs, the ghostworts are essentially indirect parasites of photosynthetic plants. Their small size and relative rarity on the landscape likely helps these plants go unnoticed by the fungi but much more work needs to be done to better understand such dynamics.

Ghostworts look more like fungi than plants.

Ghostworts look more like fungi than plants.

In 2008, phylogenetic attention was paid to the ghostworts in order to better understand where they fit on the liverwort branch of the tree. As it turns out, Cryptothallus appears to be nestled quite comfortably within the genus Aneura. Because of this, the authors suggest disposing of the genus Cryptothallus altogether. Outside of simply placing this species back in its originally described genus, it affiliation with Aneura is quite interesting from an evolutionary standpoint.

Other liverworts in the genus Aneura are also known to form mycorrhizal relationships with Tulasnella. Unlike the ghostworts, however, these liverworts are fully capable of photosynthesis. Because these intimate fungal relationships were already in place before the ghostworts began evolving towards a fully parasitic lifestyle, it suggests that the saprophytic nature of Tulasnella fungi may have actually facilitated this jump. 

The cryptic nature of the ghostworts has left many a botanist wanting. Their subterranean habit makes them incredibly hard to find. Who knows what secrets this group still holds. Future discoveries could very well add more species to the mix or, at the very least, greatly expand the known range of the other two.

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

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

 

Zoophagous Liverworts?

Mention the word "liverwort" to most folks and you are going to get some funny looks. However, mention it to the right person and you will inevitably be drawn into a world of deep appreciation for this overlooked branch of the plant kingdom. The world of liverworts is best appreciated with a hand lens or microscope.

A complete lack of vascular tissue means this ancient lineage is often consigned to humid nooks and crannies. Look closely, however, and you are in for lots of surprises. For instance, did you know that there are liverworts that may be utilizing animal traps?

Right out of the gates I need to say that the most current research does not have this labelled as carnivorous behavior. Nonetheless, the presence of such derived morphological features in liverworts is quite sensational. These "traps" have been identified in at least two species of liverwort, Colura zoophaga, which is native to the highlands of Africa, and Pleurozia purpurea, which has a much wider distribution throughout the peatlands of the world.

The traps are incredibly small and likely derived from water storage organs. What is different about these traps is that they have a moveable lid that only opens inward. In the wild it is not uncommon to find these traps full of protozoans as well as other small microfauna. Researchers aimed to find out whether or not this is due to chance or if there is some active capture going on.

Using feeding experiments it was found that some protozoans are actually attracted to these plants. What's more these traps do indeed function in a similar way to the bladders of the known carnivorous genus Utricularia. Despite these observations, no digestive enzymes have been detected to date. For now researchers are suggesting that this is a form of "zoophagy" in which animals lured inside the traps die and are broken down by bacterial communities. In this way, these liverworts may be indirectly benefiting from the work of the bacteria.

This is not unheard of in the plant world. In fact, there are many species of pitcher plants that utilize similar methods of obtaining valuable nutrients. Certainly the lack of nutrients in the preferred habitats of these liverworts mean any supplement would be beneficial.

Photo Credits: Matt von Konrat Ph.D - Biblioteca Digital Mundial (eol.org), HESS ET AL. 2005 (http://www.bioone.org/doi/abs/10.1639/6), and Sebastian Hess (http://virtuelle.gefil.de/s-hess/forsch.html)

Further Reading:
http://www.bioone.org/doi/abs/10.1639/6