Appalachian Trechus of the vandykei Group 
147 
Table 6. Analysis of gene diversity at two electrophoretic loci in 19 populations 
of five subgroups of the Trechus vandykei species group a . 
Number 
of 
Locus 
alleles 
H x 
H c/ H T 
d cs/ H t 
D sr/H t 
D rt/ H 
CAH 
7 
0.761 
0.303 
0.038 
0.673 
-0.014 
PGI 
6 
0.585 
0.582 
0.049 
0.187 
0.182 
Means 
13 
0.673 
0.442 
0.044 
0.430 
0.084 
a H T = total gene diversity. H c = gene diversity within colonies (local populations). 
D cs = gene diversity among populations within subgroups. D SR = gene 
diversity between subgroups within regions. D_ x = gene diversity between 
K. I 
regions. 
as post-Wisconsian. In fact, differentiation among populations of bowlingi 
is as great as that observed within the three “multi-isolate” subgroups 
mentioned above. The bowlingi populations, however, are sampled 
from an abundant species continuously distributed over the upland area 
in the eastern two-thirds of the Great Smoky Mountains, the most 
extensive mountain range in the region. Furthermore, bowlingi is 
sympatric and usually syntopic with different assemblages of other, 
more narrowly distributed Trechus species in different parts of its range 
(Barr 1962, 1979). Thus, differentiation in bowlingi could result from 
longer, stepwise pathways of gene flow, but it may also reflect local 
adaptation to a broader spectrum of microhabitat heterogeneity 
throughout its more extensive geographic range. 
Biochemical, biogeographical, and morphological affinities (Barr 
1979) between (a) bowlingi and the tusquitee subgroup and (b) haoe and 
the vandykei subgroup suggest a relatively recent common ancestor in 
each case. Other relationships between subgroups are vague, suggesting 
that the associated speciation events occurred in the more distant past. 
The present data do permit some speculation as to the route of dispersal 
of the vandykei species group from the southwest to the northeast 
region. As previously noted, the taxonomic hypothesis that vandykei 
and pisgahensis belong to the same biological species (Barr 1979) is 
rendered untenable on two counts: (1) the electrophoretic data indicate 
that pisgahensis (and its morphologically related Sandymush and 
Whiteside isolates) is the most distinct biochemically and least variable 
of the five vandykei- group clades, suggesting more distant affinity with 
