The NSS Bulletin - ISSN 1090-6924
Volume 47 Number 2: 89-100 - December 1985
A publication of the National Speleological Society

Regressive Evolution in Collembola
K. Christiansen

Abstract

Regressive evolution in collembola is examined in two habitats-caves and soil. Four genera are examined: Friesia, Folsomia, Schaefferia and Pseudosinella. The first genus shows regression only in soil, the second largely in soil, the third mainly in caves and the fourth almost entirely in caves. Six features show clear regression in collembola: 1) eyes, 2) furcula size, 3) tenent hair structure and size, 4) pigment, 5) unguiculus, 6) water retention ability. The first three of these were chosen for analysis. The regression of these features was examined in soil and cave forms with the goal of seeing which of the major theories used to explain regressive evolution best fitted the data observed.

The first conclusion was that there is seldom positive correlation between features displaying regressive evolution. A second is that regressive evolution in caves displays traits quite distinct from those seen in the soil. The result of these, is that different features undergoing regressive evolution behave as if they were under separate evolutionary regimes even when they are subjected to analogous selective forces.

These data do not fit an extant explanation well but are least in conflict with 1) material compensations, 2) evolutionary trap theory and 3) the indirect effect of pleitotropy, if these can be integrated so as not to be mutually exclusive.

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