146 
T. C. Kane, T. C. Barr, Jr., and G. E. Stratton 
subgroup populations (CC, BB), where it occurs at low frequency. 
However, electromorph “D” occurs in all populations in the southwest 
region and is generally the most frequent PGI electromorph in these 
populations. If dispersal from southwest to northeast took place along 
the mountains on the Tennessee-North Carolina border, it is significant 
that the “D” electromorph occurs in populations on the first two major 
summits (CC and BB) east of the French Broad River and not elsewhere. 
At the CAH locus the “D” and “F” electromorphs, which are the only 
CAH variants present in the northeast populations, are either rare (“D”) 
or absent (“F”) in southwest populations, with one exception. The 
exception is the single peripheral population of T. haoe (HA), in which 
both electromorphs occur at frequencies comparable to those seen in 
vandykei-subgrouy populations of the northeast region (Table 2). The 
pisgahensis subgroup can be distinguished from all other subgroups by 
the presence of a “null” allele at the CAH locus. This enzyme system, 
which stains intensely and consistently in the other 13 populations 
sampled, fails to yield any zones of staining in the six pisgahensis- 
subgroup populations examined. 
DISCUSSION 
Analysis of the electrophoretic data in this study suggests that 
altitudinal isolation of subgroups in the vandykei species group of 
Trechus is complete. The very great genetic differentiation between 
subgroups (F SJ = 0.533), the fixation of a unique allele in one subgroup 
(CAH locus in pisgahensis ), and the restriction of alleles to geographic 
regions (e.g. PGI electromorph “C” to the northeast region) indicate an 
absence of gene flow between subgroups and regions at present. The 
pisgahensis subgroup appears to have been isolated for the longest 
period of time. Not only does it have a unique allele fixed at the CAH 
locus, but it also shows a marked reduction in heterozygosity, which is 
consistent with long-term isolation. This result is evidence that the 
Asheville basin, which lies between the ranges of the pisgahensis and 
vandykei subgroups, may have been an effective dispersal barrier to 
these beetles even during glacial maxima; consequently, the earlier 
taxonomic treatment of vandykei and pisgahensis as geographic races of 
the same biological species (Barr 1979) requires modification. 
The degree of differentiation between populations within subgroups 
provides a basis for interpreting divergence between subgroups. For 
those subgroups whose component populations are isolated by lowland 
barriers (i.e. pisgahensis, vandykei, tusquitee), differentiation within the 
subgroup is only slight to moderate (F SJ < 0.15). Assuming that gene 
flow is no longer maintained between such isolates, these data suggest 
that the break in gene flow has been relatively recent, possibly as recent 
