Bryozoans and The Borg: Life in the collective

The Enterprise helplessly locked in the Borg’s tractor beam. Image source.

The Enterprise helplessly locked in the Borg’s tractor beam. Image source.

In Season 2, episode 16 of Star Trek The Next Generation, Captain Picard and his crew are intercepted by a nearly invincible adversary, the Borg. In a remote, unexplored section of the galaxy they encounter a cube shaped space craft manned by part biological and part machine drones that share a collective consciousness. Although individual drones have different functions, they speak with a single voice and think with a group mind. This shared consciousness grants the Borg significant advantages over their adversaries, by sharing knowledge, defensive tactics, and the allocation of resources for healing or damage repair. The Borg, responsible for the downfall of many civilizations in Star Trek, are considered to be the ultimate enemy, making it to number four on the TV Guide’s '60 Nastiest villains of all time’ in 2013'.

The siphonophore, Marrus orthocann. Image source.

The siphonophore, Marrus orthocann. Image source.

Luckily for the inhabitants of planet Earth, the Borg Collective is a figment of executive producer, Maurice Hurley’s fantastic imagination (or at the very least, we can assume that the Borg are zooming about in some quadrant of a galaxy, far, far, far away). But, what if I told you that there are borg-like creatures that can be found here on our own planet?  I’m talking about colonial organisms.  As it turns out, organisms with a colonial lifestyle are not uncommon on Earth, but their strange features are anything but common.

Imagine a string of transparent gelatinous beads wafting through the deep sea propelled forward by synchronously pumping tubes dragging behind them an elaborate network of confetti-like tentacles that contain deadly stinging cells.

Or, picture a delicate, lace-like crust covering a kelp blade that has washed up on the beach.  Upon further investigation, you discover that the crust is in fact made up of hundreds of tiny boxes, each housing a creature with a delicate crown of tentacles connected to a minuscule mouth that shyly peeks in and out from behind a doorway to sieve seawater searching for microscopic morsels of algae, pickily flinging away anything they don’t care to consume.

The bryozoan Membranipora membranacea growing on a blade of kelp. Image Source.

The bryozoan Membranipora membranacea growing on a blade of kelp. Image Source.

Both the siphonophore and bryozoan (pronounced "bray-uh-zoh-an) are examples of animal colonies.  Like the Borg, they are a collective, composed of hundreds to thousands of genetically identical (but not necessarily structurally identical) organisms living in close association with each other, working together to accomplish the tasks of life, such as eating, defending, moving and reproducing.

Colony life has some impressive benefits! Such benefits include division of labor, specialized defenses, resilience to mortality, and shared energy resources across colony members, some of the same features that warrant the Borg’s status as a vicious enemy.

The bryozoan Schizoprella japonica with its feeding apparatus (lophophore) extended. Image provided by Kira Treibergs.

The bryozoan Schizoprella japonica with its feeding apparatus (lophophore) extended. Image provided by Kira Treibergs.

Animal colonies have different levels of integration. A large gathering of a single species of seabirds can form a nesting colony on a rocky cliff face, or groups of animals can live together in eusocial societies - colonies where tasks are accomplished by separate castes of workers living together in a group. Different castes are responsible for different tasks such as reproduction, caring for the brood, foraging for food, and colony defenses. We commonly think of the eusocial insects such as some wasps, termites, ants, and bees, but there are also species of mole rat and snapping shrimp that live in eusocial colonies. For the purpose of this discussion, however, Ill focus on examples of colonial marine animals. Because their colonies are physically connected, they are the most highly integrated animal colonies and therefore the most similar to the Borg Collective.

The two ‘Borg-like animal groups we’ll explore are the cnidarians and bryozoans, however, several other groups of marine invertebrates have similarly integrated colony forms, like the tunicates, sponges, and colonial rotifers.

The Portuguese man ‘o war, Physalia physalis. Image source.

The Portuguese man ‘o war, Physalia physalis. Image source.

First, consider the phylum Cnidaria, which includes the anemones, corals, hydroids, sea pens, and several groups of jellyfish. All cnidarians are united by their specialized stinging cells used for capturing prey. One representative colonial cnidarian is the Portuguese man o’ war, Physalia physalis. What upon first glance appears to be one complete organism, a gas filled float bobbing in the waves that tows beneath it a complex tangle of venomous blue tentacles, is in fact a colony comprised of highly specialized individual animals, or zooids. The colony has specialized zooids responsible for defense and prey capture (venomous stinging cells called cnidocytes), reproduction, and digestion.  The connection between each of these zooids allows the colony to coordinate tasks and share energy resources between those individuals who have access to food resources and their neighbors who do not. Overall, this siphonophore shares many characteristics with the Borg, including integration between colony members, division of labor, a highly specialized prey capture/defense system and a way of sharing energy resources as needed throughout the colony.

The bryozoan, Bugula turrita. Image provided by Collin Johnson.

The bryozoan, Bugula turrita. Image provided by Collin Johnson.

Next, consider the phylum Bryozoa, a group whose members are colonial filter feeders found in marine and freshwater environments worldwide.  Bryozoan colonies are comprised mainly of feeding zooids, which are tiny boxes housing animals that filter feed with a ring of tentacles called a lophophore.  In addition to these feeding zooids, many bryozoan species have other zooids specializing in reproduction and defense.  For example, the species Bugula turrita has zooids with embryo brood chambers called ovicells and specialized bird-beak shaped zooids called avicularia that lie open like trap doors and can suddenly snap closed on the appendage of an unsuspecting visitor.

 

Scanning electron microscope image depicting two stalked ‘bird-beak’ zooids (avicularia) of the bryozoan, Bugula turrita. Image provide by Kira Treibergs.

Scanning electron microscope image depicting two stalked ‘bird-beak’ zooids (avicularia) of the bryozoan, Bugula turrita. Image provide by Kira Treibergs.

Much like the zooids of the siphonophore, the members of a bryozoan colony are physiologically connected to each other (all bryozoan zooids are interconnected by a branching system of tubes called the funicular network). This allows feeding zooids to share energy resources with non-feeding neighbors as well as coordinate growth within the colony.  In addition to this colony-wide coordination, division of labor, and specialized defense system, bryozoan colonies are highly resilient to colony mortality.  Predators such as flatworms, fish and sea slugs that feed on bryozoan colonies are more likely to graze on branch tips (which will readily regrow) than decimate an entire colony.

By observing the vast diversity of life forms on our planet, we can begin to ask fascinating questions about the evolution of animal life— how did the first colonial organisms evolve? Why do we see examples of coloniality across such diverse groups of organisms? What conditions encouraged the evolution of a colonial lifestyle?  While asking questions such as these, we find parallels to another great mystery, the evolution of multicellular life.  How did multicellular organisms arise from single celled ancestors? What conditions encouraged the leap from single celled life to multicellularity? Scientists may begin to uncover answers to such mysteries by studying colonial marine invertebrates.

So, science fiction aliens are not that alien after all.  We have even more strange and wonderful creatures here on earth!  Just go to the beach and inspect the blades of seaweed you find washed ashore, or peruse footage from a deep sea remotely operated vehicle (ROV) to catch glimpses of organisms whose lifestyles are far different than our own. John Steinbeck perfectly expresses the awe one feels when they encounter an animal colony in the Log from the Sea of Cortez :

“Each member of the colony is an individual animal, but the colony is another individual animal, not at all like the sum of its individuals... So a man of individualistic reason, if he must ask, 'Which is the animal, the colony or the individual?' must abandon his particular kind of reason and say, 'Why, it's two animals and they aren't alike in any more than the cells of my body are like me. I am much more than the sum of my cells, and, for all I know, they are much more than the division of me.”

Don't forget to check more on feedthedatamonster.com and stay hungry!

Kira Treibergs is a PhD student in Bob Woollacott’s lab in the department of Organismic and Evolutionary Biology at Harvard University. She received her MS in biology and developed a life-long passion for invertebrate zoology at the Oregon Institute of Marine Biology, the University of Oregon’s marine lab in Charleston, Oregon. You might recognize her as one of the creators of the Octopi Wall Street meme, which started out as a fundraiser for the Charleston Marine Life Center. When she isnt snorkeling in tide pools or inspecting the sea life growing on the sides of docks, you can find her playing bluegrass cello with friends or sailing on the Charles River.

References and further reading:

Duffy, J.E. (1996) Eusociality in a coral-reef shrimp. Nature, 381(512-514).

Harper, J.L. (1986) The growth and form of modular organisms. Eds. Brian Roy Rosen, and J. White. London, UK: Royal Society.

Hughes, R.N. Functional biology of clonal animals. Springer, 1989.

Memory Alpha (collaborative Star Trek encyclopedia)

Nautilus Live expedition

Ruppert, E.E., Fox, R.S. & Barnes, R.D. (2004) Invertebrate zoology: a functional evolutionary approach. Thomson-Brooks/Cole.

Steinbeck, J. and Ricketts, E.F. The Log from the Sea of Cortez: The Narrative Portion of the Book, Sea of Cortez. New York: Viking Press, 1951.

Vertebrate eusociality