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[Vol. 93 
Co. Ridge through some of the scattered cave systems known in the 
area. The close biochemical similarity of henroti and tellkampfi 
support this view over the alternative hypothesis that henroti 
represents a separate isolation of the surface dwelling ancestral spe- 
cies. Furthermore, Barr (1979b) notes that henroti has apparently 
not extended its range as far northward and westward as the geolog- 
ical evidence and the distribution of Hadenoecus subterraneus 
would suggest is possible. This observation, coupled with the evi- 
dence of high genetic similarity between henroti and tellkampfi, is 
supportive of a southern origin for N. tellkampfi with the range of 
henroti representing the most recent northward dispersal. 
The allozyme data fail to demonstrate a broad zone of hybridiza- 
tion between tellkampfi and viator (pattern (3) above). Moreover, 
inclusion of additional information fails to explain the discrepancy 
between the biochemical distinctness of the two taxa, on the one 
hand, and the independent evidence for a broad zone of hybrid- 
ization on the other. The lack of any geological barrier between 
tellkampfi and viator and the large degree of morphological inter- 
gradation between the two taxa (Barr, 1979b) give great support to 
the hypothesis of hybridization. Two of the viator populations 
examined in this study (i.e., C and S) lie within the zone of morpho- 
logical intergradation, making the lack of biochemical hybridization 
even more puzzling. 
Genetic differentiation in N. tellkampfi occurs primarily between 
subspecies, with high genetic similarity (S > 0.90) and only slight 
(Fst < 0.05) to moderate (0.05 < Fst <0.15) genetic differentiation 
among infrasubspecific populations. Culver (1982) reanalyzed 
Laing et al.’s (1976) data on P. hirtus and found that the average 
between area Nei index for P. hirtus populations in the ranges of 
different N. tellkampfi subspecies was I = 0.794. The average I 
between N. tellkampfi subspecies from the present study is 0.791. 
Further, analysis based on conditional allele frequencies indicates 
that gene flow level in both species can be qualitatively described as 
low. Interestingly the two species differ greatly in their ecological 
and demographic characteristics (Kane, 1982) and a substantial 
amount of evidence suggests that N. tellkampfi has a longer evolu- 
tionary history of cave isolation than does P. hirtus (Laing et al., 
1976; Barr, 1979b). 
Caccone (1985) suggests that gene flow levels and degree of 
genetic differentiation in cave species may be influenced by their 
