Research Opportunities

The bizarre adaptations displayed by troglobites make them excellent animals for evolutionary research. Recent advances in phylogenetic methods and molecular techniques provide important new tools for deciphering relationships among cave animals and their surface relatives. The discovery that close surface relatives are still extant for many tropical and island troglobites allows more appropriate comparative studies between species pairs adapted to wildly different environments. These studies should provide more critical understanding of how certain adaptations correlate with environmental parameters, as well as a better understanding of evolution in general. Some of these studies are in progress, for example, the work of Culver and colleagues on Gammarus minus in springs and caves in the eastern United States. Individual species of troglobites frequently have restricted distributions even within a given area of caves. Usually such a limited distribution indicates the existence of a barrier to subterranean dispersal, but not always. Critical morphological and behavioral studies, corroborated by modern molecular techniques, are showing that some troglobites thought to be widespread actually are composed of several more or less reproductively isolated populations. It has been assumed that cave adaptation was a dead end and that each of these populations evolved separately from the same or closely related surface ancestors that independently invaded caves. However, recent research by Hoch and colleagues on Hawaiian cixiid planthoppers suggests that some troglobites can disperse to new caves through underground voids and diverge into new species.

Caves are island-like habitats that support distinct ecosystems composed of communities of highly specialized organisms. Because the environment is discrete, rigorous, and easily defined, it provides an ideal system in which to conduct ecological studies. The number of species is usually manageable. The physical environment is rigidly constrained by the geological and environmental setting, and the environmental parameters can be determined with great precision because the habitat is surrounded and moderated by thick layers of rock. However, it is a rigorous, high-stress environment and difficult for humans to access and envision because it is so foreign to human experience. Also, one cannot enter or sample the mesocaverns where perhaps most cave animals live. These disadvantages can be overcome by comparing passages differing in the parameter of interest or by designing experiments that manipulate the parameter being studied in the natural environment. Biospeleology is still in the discovery phase. Although our understanding of cave biology has progressed substantially, results of future studies on evolution and ecology will be exciting and add significantly to our fascination with caves.

See Also the Following Articles

Aquatic Habitats • Conservation

Further Reading

Barr, T. C. (1968). Cave ecology and the evolution of troglobites. Evol. Biol. 2, 35-102.

Camacho, A. I. (ed.) (1992). "The Natural History of Biospeleology."

Museo Nacional de Ciencias Naturales, Madrid. Chapman, P. (1993). "Caves and Cave Life." Harper Collins, London. Culver, D. C. (1982). "Cave Life: Evolution and Ecology." Harvard

University Press, Cambridge, MA. Culver, D. C. (ed.) (1985). Special issue, regressive evolution. Nat. Speleol.

Soc. Bull. 47(2), 70-162. Culver, D. C., Kane, T. C., and Fong, D. W. (1995). "Adaptation and Natural Selection in Caves. The Evolution of Gammarus minus." Harvard University Press, Cambridge, MA. Hoch, H., and Howarth, F. G. (1993). Evolutionary dynamics of behavioral divergence among populations of the Hawaiian cave-dwelling planthopper Oliaruspolyphemus (Homoptera: Fulgoroidea). Pac. Sci. 47, 303-318. Howarth, F. G. (1983). Ecology of cave arthropods. Annu. Rev. Entomol. 28, 365-389.

Humphries, W. F. (ed.) (1993). The biogeography of Cape Range, Western

Australia. Rec. West. Aust. Mus. Suppl. 45. Juberthie, C., and Decu, V. (1996). "Encyclopaedia Biospeologica," Vol. I.

Soc. Biospeologie, Moulis, France. Juberthie, C., and Decu, V. (1996). "Encyclopaedia Biospeologica," Vol. II.

Soc. Biospeologie, Moulis, France. Vandel, A. (1965). "Biospeleology. The Biology of Cavernicolous Animals."

Pergamon, Oxford. [Translated by B. E. Freeman] Wilkens, H., Culver, D. C., and Humphries, W. F. (eds.) (2000). "Subterranean Ecosystems." Elsevier, Amsterdam.

0 0

Post a comment