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At Home in the Dark
| Article
# : |
11465 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
4 / 1994 |
1,743 Words |
| Author
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Branley Allan Branson
Branley Allan Branson is professor of biology emeritus at
Eastern Kentucky University and editor of the Transactions of
the Kentucky Academy of Science. |
Throughout the long evolutionary history of vertebrate animals, creatures have inexorably adapted themselves to myriad niches and environments. Sometimes body parts and chemical pathways changed to such an extent that certain animals were unsuited for life in most environments but were, instead, preadapted for life in highly specialized habitats. If those types of habitats were available, such animals moved in and were able to survive, to continue changing so that they were progressively made fitter and fitter for special ways of life,
Sometimes those special ways of life unfolded in antilife habitats--blazing deserts, hot springs, the edges of glaciers, the maritime abyss--but none of those special environments were any more formidable than caves. Eternal darkness and bone-chilling temperatures prevail century after century and food chains are meager in the extreme, based on organic materials being swept in from above or being brought in by animals, like bats, that are not entirely cave adapted. Competition for the wherewithal of life is extreme, forcing the cave coteries to maintain small populations and keep individuals well separated from one another.
Not many animals were preadapted for this kind of life. In America, true cave-dwelling vertebrate animals are few in number, mostly a few kinds of salamanders and a handful of fish species. Of all these, none are more thoroughly cave adapted than the weird-looking members of the cave fish family of the unglaciated part of the eastern United States.
Although a few members of other fish families in other parts of the world live in caves-there are also two blind subterranean catfishes known from the aquifers of Texas (Satan euiystorn us and Thogloglanis pattersoni)--none have become as thoroughly modified for this kind of life as have the most extreme species of the American family Amblyopsidae. The six living species of the family demonstrate graphically how the process of evolution for darkness probably came about.
Special modifications
Because not one person in a million has ever seen an American cave fish, we must describe these interesting little creatures. The family is divided into four genera--some ichthyclogists say five--and six species, and all family members share certain characteristics. All dwell in swamps, springs, or caves and have very small, reduced eyes or no eyes whatsoever. The pelvic fins are extremely small or nonexistent, and certain skeletal elements are
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