134 
John R. Holsinger and David C. Culver 
as Form I in a given cave. These two forms are never found together in 
the same cave, although they sometimes inhabit caves no more than 5 to 
10 km apart. 
In a previous study (Holsinger and Culver 1970), in which the 
morphological variation of this species was carefully analyzed, we 
concluded that the three forms probably represented different eco- 
phenotypes of a single, highly variable species. However, we were 
unable to give a satisfactory explanation for the presence of Form I in 
only two isolated karst areas, except to suggest that it might represent a 
convergent ecotype that occurs only under special environmental 
conditions in the presence of proper genetic variants. Both of these karst 
areas are similar in that they contain large, integrated subterranean 
drainage systems. On the other hand, Form II populations are also 
sometimes found in caves that are components of extensive subterranean 
drainage systems and, in some instances, not far removed geographically 
from caves with Form I populations. 
Genetic studies on G. minus , principally in the Greenbrier Valley of 
West Virginia, by Hetrick (1975), Hetrick and Gooch (1981), and Gooch 
and Hetrick (1979), in which allozyme allele frequencies were determined 
at three polymorphic loci, tend to support the ecophenotype concept. 
The results of these studies indicate that there is generally a greater 
genetic distance between populations of the same ecophenotype in 
different geographic areas than between populations of different 
ecophenotypes in the same small, defined geographic area, and that 
most of the sharper discontinuities coincide closely with potential 
barriers to dispersal, such as streams, stream and karst drainage divides, 
and stratigraphic changes. 
Whether the troglomorphic populations in Ward Cove and the 
Great Savannah are already incipient troglobitic species, are on their 
way to becoming separate species, or simply represent the extreme 
expression of a highly plastic phenotype is debatable and cannot be 
resolved on the basis of the information presently available. Further 
study is clearly needed. 
Terrestrial Species . — The origin of terrestrial troglobites has perhaps 
been more direct and has involved fewer variables than that of aquatic 
troglobites. Most workers agree that the troglobitic terrestrial fauna of 
the north temperate region (viz., North America, Europe, and Japan) 
has been derived from preadapted, epigean ancestors that occupied 
moss, ground litter, and deep-soil habitats of humid forest floors (see 
Vandel 1965b, Barr 1968, Peck and Lewis 1978, Peck 1981b, Culver 
1982, Barr and Holsinger 1985). Moreover, the invasion and colonization 
of caves by terrestrial invertebrates has probably been, and still is, an 
ongoing process, involving the dynamics of taxon cycles and pulses (see 
also Peck 1980, 1981b). With few exceptions, all terrestrial troglobites in 
