Volume 39, Number 1,
October 1992:
Springtails

Text-only version

ABOUT THIS ISSUE
- about KSN
- about the author

IN THIS ISSUE
- part 1
- part 2
- part 3
- part 4
- part 5
- part 6
- part 7
- part 8
- part 9
- part 10

SLIDESHOW
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Springtails
by Kenneth Christiansen

Caves are another habitat with conditions very favorable for Collembola. In spite of this, and the fact that many individuals accidentally fall or are swept into caves, relatively few species can survive and reproduce in caves. Almost all surfaces species such as Folsomia candida which are found in caves, are opportunistic invaders, unable to face competition from species which are specially evolved for cave life. The opportunistic forms are trapped by water pools and have difficulty moving over the water-filmed surfaces. The forms which have evolved for a long time in caves (called troglomorphs) have feet adapted for water surfaces and run over them with ease. Collembola make many evolutionary adaptations to caves, including conspicuous elongation of appendages and increased size. These evolutionary changes have occurred independently in cave systems all over the world to produce highly evolved members of different genera and tribes, all resembling the large Pseudosinella christianseni (Figure 19). Whether you are looking at caves in Australia, Europe, North America or Japan you can be certain that highly evolved cave forms of the family Entomobryidae will look like this. These forms bear a striking superficial similarity in body form to species found in the trees in tropical regions. However, unlike them they lack both pigment and eyes and their feet resemble those seen in aquatic species such as Sminthurides aquaticus. In lack of pigment or eyes, they resemble the deep soil forms.

Cave Collembola also show striking physiological adaptations for cave life. As springtails evolve species become more and more adapted to cave life, they tend to become intolerant of minor changes in environmental conditions, even though some species have lost the ability to detect and respond to such changes. In contrast to this delicacy in relation to physical conditions, many of these cave forms have a remarkable capacity to endure starvation, and some remain alive in culture for more than two years with only distilled water added to a bare substrate of charcoal and plaster.

Collembola may not actually be quite as indifferent to the food supply as this observation suggests. While they may prefer certain foods, most species are capable of surviving on a wide variety of materials, including fecal matter and bacteria. Thus they are able to reprocess their own wastes. In one experiment with specimens living on clay, it was found that the organic matter of the surface layer had increased after 8 months during which only distilled water had been added. According to an even more remarkable report, a population of Folsomia candida increased in numbers on a substrate of glass beads to which only distilled water was added. A possible explanation of this apparent violation of the laws of thermodynamics is that the Collembola were obtaining energy not only from their own cast skins and feces but from microorganisms introduced into the culture as airborne spores.