What Do You Eat When You're Subterranean?
Underground races add spice to many fantasy worlds, but keeping them from starving requires a few more ingredients. All life forms need a source of energy to fuel their ongoing (and ultimately losing) battle with entropy. There are two basic strategies for obtaining energy on Earth. Some organisms, called autotrophs or "self-is-food," can capture energy from non-living sources in their environment. The others, called heterotrophs or "other-is- food," eat organic materials (such as autotrophs, heterotrophs, decaying bodies, or waste products) that contain energy originally captured by autotrophs. An underground race can eat autotrophs or heterotrophs or be autotrophs and capture their own energy.
On Earth, all energy-capture strategies (two autotrophic methods plus heterotrophism) were developed by various bacteria. Photosynthesis, the ultimate basis for nearly all life on the planet, captures the energy of sunlight. Chemosynthesis, the only known autotrophic exception to photosynthesis, captures the energy released when inorganic substances are oxidized. Heterotrophs are fueled by oxidizing organic compounds created by other living things. Rather than come up with something new, the ancestors of multi-celled life shanghaied one or more types of bacteria and converted them into little "engines" for their cells. Plants have chloroplasts (descended from photosynthesizing bacteria) and mitochondria (descended from heterotrophic bacteria). Fungi and animals have only mitochondria. It may seem odd that plants have mitochondria, but they need to live even when the sun is not shining. They store sunlight energy in organic compounds and use their mitochondria to tap it later.
Underground autotrophs have to use a means of energy capture other than photosynthesis, because sunlight is rare in deep caverns. The only known autotrophs that do not photosynthesize are chemosynthetic bacteria. They oxidize such inorganic substances as elemental sulfur, thiosulfate, hydrogen sulfide, ammonia, nitrite, ferrous ions, or hydrogen gas, depending on the species. Most require oxygen, though not necessarily in high concentrations. Some types live in aerated soil and play key roles in the planetary sulfur and nitrogen cycles. Some grow in hot springs, such as those in Yellowstone Park. Other types live on the ocean bottom near sources of hydrogen sulfide and methane. These include hydrothermal vents (underwater volcanoes), whale carcasses, and cold-seeps. In cold- seeps, sulfate and methane from groundwater or sediments are converted to hydrogen sulfide by specialized bacteria.
Humans eat bacteria in vinegar, yogurt, and cheese, but cultivating a foodstuff composed exclusively of microscopic organisms might be challenging. The bacteria humans eat are in an organic medium, such as milk, which is itself a nutritious source of digestible energy. Chemosynthetic bacteria, on the other hand, have mediums such as soil or sulfur water. Luckily, there is nothing to prevent the GM from stepping in and inventing a multi-celled autotroph with chemosynthetic "chloroplasts." This would be an entirely new kingdom, and the GM would have enormous latitude in creating its characteristics. It could easily be as different from plants as the two heterotrophic kingdoms, animals and fungi, are from each other. It could grow in underground hot springs like seaweed or prowl caverns in search of the right sediments. The new kingdom might have a single species or thousands, might be common or extremely rare. It could be a refugee from an ancient time, dependent on the race it sustained. A real-life example of a species carried over from an earlier age by human intervention is the ginkgo, a beautiful and once- common tree that probably began to die out when dinosaurs stopped spreading its seeds. It may owe its existence today to being cultivated for centuries in Chinese monasteries and palace gardens.
Of course, the GM need not be limited to the energy-capture mechanisms found on Earth. Other energy sources could theoretically support autotrophic life. The GM could invent bacteria that utilized these sources . . . or even go so far as inventing multi-celled organisms that, at the dawn of time, had press-ganged the fantasy bacteria into providing them energy-capture services.
Hot objects emit photons (mostly in the infrared), and these could be captured and utilized in a manner very similar to photosynthesis. For example, an organism could capture energy from the heat radiated by a magma pool. Of course, magma chambers are not known for being particularly safe or stable habitats. Underwater, life can only capture heat energy indirectly, because the radiated photons are quickly absorbed by the water. However, heat can add energy to chemical reactions and make them potential sources of chemosynthetic energy. For example, at hydrothermal vents, magma superheats seawater, which causes the water to react with dissolved sulfate. The heat energy is stored in the chemical bonds of hydrogen sulfide. Chemosynthetic bacteria break these bonds and capture the stored energy. The bacteria release sulfate as a waste product, and the sulfur cycle closes. This situation could also exist in caverns, in an underground stream bathing a magma pocket, for instance. This type of heat energy capture is not feasible on land because everything is roughly at equilibrium and lacks the necessary steep temperature gradients.
Radioactive elements are present underground, and a fantasy bacterium might harvest radioactive energy. Tending radiosynthetic species, happily growing on uranium deposits, could be a challenge for the farmers. The invented species would have to be less sensitive to radioactive damage than Earth species are. This is not as unreasonable as it seems. Oxygen is very reactive and was probably highly toxic to the original life on Earth (when oxygen was rare), but modern life is quite oxygen tolerant.
Many fantasy worlds have an additional source of energy: raw magic. A very clear idea of what mana is and how it behaves would be helpful when inventing a manasynthetic species. Is mana restricted to mages or does it exist in the environment? If only mages can produce mana, then a manasynthetic species would probably be created and sustained by them, like an animated skeleton. However, if mages have inhabited the world for a billion years, life forms could have evolved to capture energy from them. Also, being created by mages does not preclude a certain amount of autonomy if the spell is self- sustaining. For example, a mage may have created autotrophs with a self-propagating create-food spell. Modern mages would have to know the spells necessary to supply the autotrophs with energy, but would not necessarily know how to create more of them.
If mana is a natural energy, akin to radiation, free-living manasynthetic species could have evolved independently. Then the question is whether a mana source always radiates the same amount of energy. Plants, especially plants grown under low light, can be severely damaged when suddenly exposed to high photon flux densities. Therefore, sudden pulses of mana or large magical discharges could have disastrous consequences for underground manasynthetic farms.
If the members of the underground race do not eat autotrophs (and are not autotrophs themselves), they will have to live on heterotrophs. Heterotrophs require access to organic material, created ultimately by autotrophs. If those autotrophs are photosynthetic, the organic material will have to be transported underground after it is created. One way to move organic material is for the race to carry it. The gardening ants are a real-life example of an underground race that eats fungus raised on plant material that they bring down from the surface.
The underground race will probably have a source of water in their caverns. If the water flows from the surface, it could carry a load of organic materials: leaf detritus, insects, microorganisms, partially decayed animals. These could be consumed by heterotrophic bacteria, fungi, non-green plants, insects, or even fish. In a similar manner, most of the primary energy for many stream ecosystems is supplied by the land plants that grow along their banks. Fungi could theoretically bring organic material underground for themselves. A mushroom is the relatively small reproductive structure of a large fungus that snakes in nearly invisible threads throughout the soil. So if it is possible to reach the soil layer from the cavern, it is reasonable to imagine a fungus that "fruits" underground. Truffles actually do, but in the soil, not in caves.
Of course, a cave is not a good place for a mushroom. Above-ground, wind can spread its spores, and gravity will deposit them on the rich, top layer of soil. Young fungi can begin life in a smorgasbord of partially decayed organic matter. This would not be the case underground. Left to its own devices, this fungus mutant would probably die out quickly. However, a mutant that could not survive naturally will do fine with outside help. For example, the bananas in the grocery store are the seedless fruit of a sterile plant -- evolutionarily a dead end, but faithfully cultivated by banana-eating humans. If the underground race could find a single mutant with subterranean mushrooms, they could then help it to survive. They might have to gather the spores and stick them to the roof of a cavern to get them nearer the surface. Perhaps they would have to fertilize the newly sprouted spores (with the bodies of dead dwarves?) so the young fungi could survive until they reached the organic material in the upper soil layers. The race would want to control most of the caverns in the vicinity, since the fungus would probably send out mushrooms wherever it pleased.
One problem with fungi is digestibility. Fungi are a good source of some vitamins, minerals, and proteins, but they contain very little fat, sugar, or calories -- that is, digestible energy. That might be encouraging to dieters, but it makes them a poor choice for a race's primary energy source. Most of the carbohydrates in fungi are in the form of difficult-to-digest chitin cell walls. Plants have cell walls of equally indigestible cellulose. Most herbivores cultivate specialized, cellulose-digesting, heterotrophic bacteria in their stomachs to make it possible for them to eat plants. Tolkien probably did not envision ruminant dwarves, but it could be done.
On the other hand, the bacteria could be applied externally, the same way humans make yogurt. Since yogurt-making is beyond Stone Age technology, such a race would have been reasonably advanced before they stopped foraging on the surface and began to live exclusively underground. (Yogurt is made by heating the medium to destroy dangerous -- or just yucky -- bacteria from the environment, adding a little yogurt bacteria culture, stirring, and keeping it gently warm until the bacteria multiply and partially break down the medium.) Death or loss of the starter culture would be fatal for such a race. Analogously, queen gardening ants carry starter fungus on their nuptial flights, and if the starter is lost or dies, the new colony is doomed.
Gardening ants solved the problem of obtaining digestible energy from fungi by "selectively breeding" domestic fungi with traits that wild fungi do not have. Some domestic fungi secrete specialized enzymes onto the leaf-fragment beds the ants prepare for them. The enzymes break down the leaves and cause sugars to form on them. These sugars are then licked up by worker ants. The fungi also produce tiny, nutrient-rich "fruit." Fungus domestication is obviously possible. However, unless one is playing Ants and Burrows, it might be difficult to sustain an RPG race on the swollen tips of mold hairs and sugar licked off a fungus.
Decaying material in soil is not the only source of organic compounds found underground. Methane is often found in fossil fuel deposits, and bacteria that oxidize methane are an important energy source for communities such as those on cold-seeps. Certain heterotrophic bacteria are able to use petroleum as an energy source. However, fossil fuels are often loaded with heavy metals. The bacteria (and presumably invented species using the same energy source) are able to deal with this, but that does not necessarily make them edible. Many surface plants that are heavy metal tolerant take the metals up and concentrate them in their tissues. An underground race with such a food source would have to have a means of dealing with high levels of heavy metals, either externally (through food preparation technology) or internally (by being tolerant themselves).
Transport ceases to be a problem if the autotrophic source of organic materials is already underground. A GM could have the race farm heterotrophs that eat one of the chemosynthetic, radiosynthetic, or manasynthetic autotrophs already discussed.
An unusual source of organic material for a radically designed fantasy world is true spontaneous generation. It is believed that the first life on Earth was heterotrophic and lived on spontaneously generated organic material. Laboratory experiments have successfully replicated such spontaneous generation, but only under conditions that bear little similarity to modern-day Earth. Early Earth probably had warm, shallow oceans, active volcanoes, and radioactive rocks under an atmosphere of water vapor, carbon dioxide, carbon monoxide, nitrogen, methane, and ammonia. The atmosphere was alive with energy, rent by lightning and bombarded with ultraviolet radiation. Molecular oxygen was essentially absent, and an oxygen- rich atmosphere seems to make the spontaneous generation of organic material impossible. Since lightning and ultraviolet radiation are not too common underground, the GM will have to use an alternative energy source such as radioactivity, volcanism, or magical discharges. Such conditions might even be possible on an Earth-like world in completely sealed caverns. For a race from such caverns, the surface would have a hostile, poisonous atmosphere. Traveling there would be like visiting another planet. The race would probably require a life-support suit (or a protection-from-oxygen spell) and not be able to digest surface food. Another difficulty with spontaneously generated organic matter is that it does not accumulate quickly. It probably inspired the early evolution of all existing energy-capture methods by becoming scarce.
In some organisms that the underground race might eat, the line between heterotrophs and autotrophs blurs. This happens when a heterotroph and an autotroph form a partnership and live entwined with each other. The heterotroph usually provides defense and raw materials from the environment; the autotroph captures energy for them both. The heterotroph is usually much larger and accounts for the appearance of the combo-organism. On land, heterotrophic fungi and autotrophic bacteria or algae form partnerships known as lichens. In cold-seeps and hydrothermal vents, several types of animals, including shrimp, worms, mussels, and clams, have formed partnerships with chemosynthetic bacteria. A GM wishing to create one of these life forms should realize that the major difference between them and true autotrophs is that the partnership was formed much more recently than the dawn of life on Earth. Therefore, both partners have close relatives that are not married (not all fungi are lichens). Sometimes the partners can be separated, if only in a laboratory, and grow independently. The autotrophs usually live within their partners' bodies, not within their cells. Lichens look much different than free-living fungi, because the fungus grows compactly instead of branching out in search of food. The autotroph partners in lichens are photosynthetic, but fantasy lichen could have chemosynthetic, radiosynthetic, or manasynthetic bacteria. Several lichens have been traditionally eaten by humans, including the arctic reindeer moss and desert manna lichen. Since the energy source is the autotrophic partner, lichens may be a better source of digestible energy than are fungi.
Certain shrimp farm chemosynthetic bacteria on their exoskeletons and feed their farms by swimming to "fields" of dissolved sulfur compounds. The shrimp then graze bacteria off their own bodies. Tube worms supply their bacteria with inorganic carbon, oxygen, hydrogen sulfide, and nitrate that they absorb from the surrounding water. The substances are transported in the worm's blood to the internal organ where it keeps its bacteria. The worms then excrete the bacteria's waste products: sulfate and protons. The worms may live to be 250 years old in the stable environment of cold seeps. Adult tube worms have no mouths or digestive systems since, like plants, they have an internal energy source. It is believed that the larvae are born with mouths and eat their bacteria when they begin life.
One type of mussel contains two kinds of bacteria: some that oxidize methane and some that oxidize sulfur compounds. Presumably, this allows it to change gears if one source of energy is depleted. Clams partnering with chemosynthetic bacteria harbor these bacteria within the cells of their gills. The bacteria are passed on to the next clam generation in the eggs. The partnership is so tight that attempts to culture the bacteria independently in the laboratory have failed. These clams are probably the closest thing on Earth to a chemosynthetic plant.
An adventurous GM might want to have an underground race whose members are combo-organisms and have their own internal engines cranking out energy. This does not mean that the race can just sit back and forget about food, however. They will have to supply their internal autotrophs with all the minerals, fluids, and gases they require as raw materials.
Some GMs will prefer designing a single food-species for their underground race, since it involves less work (and fewer opportunities for over-zealous players to ask sticky questions). However, many of the problems discussed above cease to be an issue if the underground race is part of a diverse ecosystem. Mushrooms or lichens do not have to be perfectly digestible if, as is the case for humans, they make up only part of the diet. Having sufficient hot- spring surface area to cultivate paper-thin bacterial mats is not so critical when they are a delicacy and not the race's sole source of energy. There are a few real world examples of ecosystems based entirely upon chemosynthetic bacteria.
The most famous chemosynthesis-based ecosystems are at deep-sea hydrothermal vents. Chemosynthetic bacteria oxidizing sulfur compounds support a host of heterotrophs such as fish, shrimp, snails, crabs, clams, mussels, barnacles, sponges, and octopuses. Tube worms can grow to more than a meter long, easily large enough to sustain an underground RPG race. This type of ecosystem is not restricted to the deep, lightless regions of the ocean, but it is much more striking in places devoid of photosynthesis-based life.
An example of a chemosynthesis-based cavern ecosystem is in Movile Cave in Romania. It consists of limestone caves partially submerged in hot springs that are rich in hydrogen sulfide, ammonium ions, and methane. Prior to discovery, the caves were sealed off from the world above. They have a specific atmosphere enriched in methane with up to ten times more carbon dioxide and one third less oxygen than the outside air. Microbial mats made up of bacteria and fungi float on the water surface, adhere to cave walls and sit on submerged cavern floors. Bacterial species include some that oxidize methane and some that oxidize sulfur compounds. The deep waters of the cave have no oxygen, so the submerged mats may consist entirely of heterotrophs that feed on methane or material falling from above. The microbial mats feed terrestrial and aquatic animals such as snails, worms, pillbugs, millipedes, springtails, and bristletails. Carnivores include blind predatory leeches, water scorpions, pseudoscorpions, centipedes, and spiders. The chemical differences between photosynthesis and chemosynthesis likely mean that, in a closed system like Movile Cave, the development of an unusual atmosphere is inevitable. However, a chemosynthetic ecosystem can probably form even if the cavern's atmosphere is not isolated from the surface. (The Movile Cave system has apparently survived being exposed to the surface by the shaft its discoverers constructed.)
Designing an ecosystem requires extra effort, but it will make the underground race more sustainable and less susceptible to famine disasters. The first building block of an ecosystem is an energy source. The GM can use one or several of the energy sources discussed here. Each energy source needs at least one autotrophic species to capture it. Bacteria are the most likely autotrophs, but they can be supplemented by some multi-celled species. Heterotrophic microbes and insects could graze on the bacteria and provide food for larger predators. Decomposers (usually bacteria and fungi) must be present to prevent the ecosystem from collapsing with all its raw materials tied up in dead bodies and waste products. Each ecosystem component is a potential source of food. For instance, the underground race might sweeten their lichen tea with ants full of leaf-mold sugars, roast the moles that live on bacteria-grazing insects, spicing them with microbial mat (for that sulfur tang), and make salads of subterranean mushrooms and chemosynthetic seafood, sprinkled with manasynthetic lice the mage combs out of his beard.
Even lichen-like organisms might benefit from a varied diet. Hunting down outside sources of energy is probably not effective for something with an internal energy source, but the race might eat to gain nutrients. Carnivorous plants, for example, cannot obtain sufficient nitrogen from the soils they prefer, so they photosynthesize for their energy and eat insects as a nitrogen source. Feeding an underground race requires, first and foremost, a source of energy. The GM will have to decide what this energy source is and how the race acquires it. This includes deciding if they are using the energy source directly (autotrophic), eating something that can utilize the energy source (eating autotrophs), eating something that is getting its energy from other living organisms (eating heterotrophs), or cultivating an autotroph inside their bodies (acting like a lichen). Some energy sources can be present underground naturally (precursors to chemosynthesis, heat, radioactivity, mana). Others, like sunlight, have to be transported there. Organic compounds produced using sunlight can be transported by the race or by water, transported by the food source (hypothetical underground mushrooms), or buried (coal and oil). Although it is possible to design a race with a single food source, creating an ecosystem with a combination of energy sources and food types provides more variety and may ultimately make for a more interesting game.
For the Sake of Appearances
"Plants" based on chemosynthetic bacteria would probably not be green, since the green color comes from pigments used in photosynthesis. Some bacteria that oxidize hydrogen sulfide have particles of inorganic sulfur in their cells, for instance. Images from Movile Cave can be found in the documentary Ends of the Earth: The Secret Abyss of the Movile Cave. The following websites also have images of chemosynthetic life on Earth.
Bacteria That Oxidize Sulfur Compounds
* Thiothrix --
http://www.lpi.usra.edu/education/EPO/y ... bvspring1/
* Sulfolobus --
http://web.umr.edu/~microbio/BIO221_199 ... ricus.html
* Sulfolobus --
http://biology.kenyon.edu/Microbial_Bio ... lobus.html
Bacteria That Oxidize Nitrogen Compounds
* Nitrosomonas --
http://biology.kenyon.edu/Microbial_Bio ... monas.html
* Nitrosospira --
http://genome.jgi-psf.org/finished_micr ... .home.html
Bacteria That Oxidize Iron Compounds
* Thiobacillus ferrooxidans --
http://bugscope.beckman.uiuc.edu/member ... 40x480.jpg
Bacteria That Oxidize Hydrogen Gas
* Xanthobacter --
http://141.150.157.117:8080/prokPUB/cha ... MPLETE.htm
Animals with Chemosynthetic Bacterial Partners
* Tube worms, Riftia --
http://www.marinetech.org/nine_degrees/ ... e_worm.jpg
* Tube worms, Riftia --
http://pubs.usgs.gov/gip/dynamic/tube_worms.html
* Clams, Calyptogena --
http://walrus.wr.usgs.gov/hydrocarbons/clams.html
* Mussels, Bathymodiolus --
http://oceanexplorer.noaa.gov/explorati ... ussel.html
* Shrimp, Rimicaris exoculata --
http://www.geocities.com/magnus_johnson ... h/rimi.htm
Cave Microbial Mats
*
http://www.geo.utexas.edu/chemhydro/Low ... bitats.htm
Cold Seeps and Hydrothermal Vents
*
http://www.mbari.org/news/homepage/2005 ... #aboutcbcs
*
http://www.ifremer.fr/exocetd/gb/gallery/galleryeco.htm
*
http://www.noc.soton.ac.uk/ventox/files ... /atos.html
Consulted materials:
* Campbell, Neil A. 1990 and 1993. Biology. Second and Third editions. The Benjamin/Cummings Publishing Company, Inc. Redwood City, California.
* Niklas, Karl J. 1997. The Evolutionary Biology of Plants. The University of Chicago Press. Chicago, Illinois.
* Raven, Peter H., Ray F. Evert, and Susan E. Eichhorn. 1992. Biology of Plants. Fifth edition. Worth Publishers. New York, New York.
* Taiz, Lincoln and Eduardo Zeiger. 1991. Plant Physiology. The Benjamin/Cummings Publishing Company, Inc. Redwood City, California.
--Sierra Dawn Stoneberg Holt
