Troglofauna are small

cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...

-dwelling

animal Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...

s that have adapted to their dark surroundings. Troglofauna and stygofauna are the two types of

subterranean fauna file:P anguinus1.jpg, The olm (''Proteus anguinus''), a typical cave dwelling chordate, Endemism, endemic of Dinaric Alps Subterranean fauna refers to Animal, animal species that are adaptation, adapted to live in an underground Natural environmen ...

(based on life-history). Both are associated with subterranean environments – troglofauna are associated with caves and spaces above the water table and stygofauna with water. Troglofaunal species include

spider Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider silk, silk. They are the largest order of arachnids and ran ...

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

myriapods Myriapods () are the members of subphylum Myriapoda, containing arthropods such as millipedes and centipedes. The group contains about 13,000 species, all of them terrestrial. Although molecular evidence and similar fossils suggests a diversifi ...

and others. Some troglofauna live permanently underground and cannot survive outside the cave environment. Troglofauna adaptations and characteristics include a heightened sense of hearing, touch and smell. Loss of under-used senses is apparent in the lack of pigmentation as well as eyesight in most troglofauna. Troglofauna insects may exhibit longer

appendage An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...

s and a lack of wings.

Ecological categories

Troglofauna are divided into three main categories based on their

ecology Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...

: * Troglobionts (or

troglobites A troglobite (or, formally, troglobiont) is an animal species, or population of a species, strictly bound to underground habitats, such as caves. These are separate from species that mainly live in above-ground habitats but are also able to live u ...

): species, or populations of species, strictly bound to subterranean habitats. * Troglophiles: species living mainly aboveground but also in subterranean habitats. These are further divided into eutroglophiles (aboveground species also able to maintain a permanent subterranean population) and subtroglophiles (species inclined to perpetually or temporarily inhabit a subterranean habitat, but strongly associated with aboveground habitats for some functions). *

Trogloxene Trogloxenes or subtroglophiles, also called cave guests, are animal species which periodically live in underground habitats such as caves or at the very entrance, but cannot live exclusively in such habitats. Among many scientists, trogloxenes and ...

s: species only occurring sporadically in an underground habitat and unable to establish a subterranean population.

Environment

Troglofauna usually live in moderate cave regions. The overall climates of these caves do not significantly change throughout the year. Humidity in such caves is generally high ranging from 95 to 100 percent; evaporation rates are low. The cave ecosystem in which troglofauna reside can be divided into four zones: entrance, twilight, transition and deep cave. The entrance zone is where the surface and underground environments meet. Light becomes scarcer in the twilight zone. The transition zone is almost completely dark; however some outside environmental effects can still be felt. Finally, the deep cave zone is completely dark, relatively stable, and exhibits no evaporation. Troglobites are usually found in the deep cave zone.

Diet and lifecycle

Troglofauna have adapted to the limited food supply and are extremely energy efficient. Food is found from "twigs, leaves, bacteria and

epigean Epigeal, epigean, epigeic and epigeous are biological terms describing an organism's activity above the soil surface. In botany, a seed is described as showing epigeal germination when the cotyledons of the germinating seed expand, throw off the ...

animals (including

zooplankton Zooplankton are the heterotrophic component of the planktonic community (the " zoo-" prefix comes from ), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequent ...

)." Food is also found from trogloxene carcasses, egg deposits, and faeces such as bat guano. Troglofaunal beetles are predators and may feed on other troglofaunal animals rather than bacteria, twigs and guano. Francis G. Howarth hypothesized on adaptations troglofauna have made to exist in the cave environment, postulating that troglofauna "have lost many of the water conservation mechanisms of surface relatives, and more nearly resemble permanently aquatic arthropods in water balance mechanisms, including cuticular permeability." Troglofauna thrive in a humid environment and when a "chamber is too dry ... animals display either agitated or comatose behavior", indicating they are highly susceptible to changes in temperature and humidity. To survive in an environment where food is scarce and oxygen levels are low, troglofauna often have very low

metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...

. As a result, troglofauna may live longer than other terrestrial species.

Reproduction

Reproduction varies by species and may be infrequent, but very little is known.

Evolution and dispersal

Troglofauna have evolved in isolation.

Stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...

barriers, such as rock walls and layers, and

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

barriers, such as rivers and streams, prevent or hinder the dispersal of these animals. Consequently, troglofauna habitat and food availability can be very disjunct and precluding a great range in diversity across the landscape.

Species

Troglofaunal species include representatives of many animal groups, including

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

centipedes Centipedes (from Neo-Latin , "hundred", and Latin language, Latin , "foot") are predatory arthropods belonging to the class Chilopoda (Ancient Greek , ''kheilos'', "lip", and Neo-Latin suffix , "foot", describing the forcipules) of the subphyl ...

millipede Millipedes (originating from the Latin , "thousand", and , "foot") are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derive ...

pseudoscorpion Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like arachnids belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida. Pseudoscorpions are generally beneficial to humans bec ...

harvestmen The Opiliones (formerly Phalangida) are an Order (biology), order of arachnids, Common name, colloquially known as harvestmen, harvesters, harvest spiders, or daddy longlegs (see below). , over 6,650 species of harvestmen have been discovered w ...

isopods Isopoda is an Order (biology), order of crustaceans. Members of this group are called isopods and include both Aquatic animal, aquatic species and Terrestrial animal, terrestrial species such as woodlice. All have rigid, segmented exoskeletons ...

collembola Springtails (class Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects. Although the three lineages are sometimes grouped together in a class called Entognatha because they have internal m ...

ns,

diplura The order Diplura ("two-pronged bristletails") is one of three orders of non-insect hexapods within the class Entognatha (alongside Collembola (springtails) and Protura). The name "diplura", or "two tails", refers to the characteristic pair o ...

ns,

beetle Beetles are insects that form the Taxonomic rank, order Coleoptera (), in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 40 ...

s and

salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...

s. Troglofaunal gastropods are endemic to the U.S. and in Europe; they are mostly concentrated in the northeastern Mediterranean regions. Troglofaunal scorpions are mostly found in Mexican caves. Troglobitic spiders are found more widespread in the U.S., Europe, and Japan. However, they are also found in

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

, the Congos (the

DRC The Democratic Republic of the Congo (DRC), also known as the DR Congo, Congo-Kinshasa, or simply the Congo (the last ambiguously also referring to the neighbouring Republic of the Congo), is a country in Central Africa. By land area, it is t ...

and the

RotC The Reserve Officers' Training Corps (ROTC; or ) is a group of college- and university-based officer-training programs for training commissioned officers of the United States Armed Forces. While ROTC graduate officers serve in all branches o ...

Cuba Cuba, officially the Republic of Cuba, is an island country, comprising the island of Cuba (largest island), Isla de la Juventud, and List of islands of Cuba, 4,195 islands, islets and cays surrounding the main island. It is located where the ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

, and the

Philippines The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...

. Troglofauna are found worldwide. Troglofaunal salamanders are found in Europe and the U.S. Many caves remain undiscovered due to lack of visible entrances and more habitat exists in fissures,

vugs A vug, vugh, or vugg () is a small- to medium-sized cavity inside rock. It may be formed through a variety of processes. Most commonly, cracks and fissures opened by tectonic activity ( folding and faulting) are partially filled by quartz, calc ...

and other spaces above the watertable. Consequently, many species of troglofauna may not have been discovered.

Discovery

More troglofaunal species are being identified. A report from 2007 described how scientists had recently discovered 255 new caves and 30 undescribed invertebrate species in Sequoia and

Kings Canyon National Park Kings Canyon National Park is a national park of the United States in the southern Sierra Nevada, in Fresno and Tulare Counties, California. Originally established in 1890 as General Grant National Park, the park was greatly expanded and ren ...

s of Sierra Nevada mountains, California – "an extraordinary number for such a small area".

Threats to troglofauna

Floodwaters can be detrimental to troglofaunal species, by dramatically changing the availability of habitat, food and connectivity to other habitats and oxygen. Many troglofaunal species are likely to be sensitive to changes in their environment and floods, which can accompany a drop in temperature that may adversely affect some animals. Extreme winter temperatures may affect troglofaunal species near the surface. Birds and bats in caves prey on troglofauna. Troglofauna are likely to compete with each other for survival. Humans also pose a threat to troglofauna. Mismanagement of contaminants (e.g. pesticides and sewage) may poison troglofaunal communities, whilst removal of habitat, either directly or indirectly (e.g. rising watertable) is also a major threat.

References

External links

"Flora and Fauna of Caves: Troglobites" at Showcaves.com

* * {{Cite news , url=https://news.mongabay.com/2024/03/rising-temperatures-threaten-the-tiny-animals-responsible-for-groundwater-quality/ , title=Rising temperatures threaten the tiny animals responsible for groundwater quality , author=Bernardo Araujo , work=Mongabay , date=18 March 2024 Cave animals Subterranea (geography)