78 WF. Ponder, D.J. Colgan, T. Terzis, S.A. Clark, A.C. Miller 
D. globosa Cb 
Ca 
Cal (D24) 
A 
B 
Ca 
Cd 
Cc 
Ch 
Da 
Db 
D. harrisi E 
Ga 
H1 
F 
H3 
+----+----+----+----+----+----+----+----+----+----+----+----+ 
.20 .17 .13 .10 .07 .03 .00 
Figure 23. Phenogram showing relationships of Dalhousia based on unweighted pair group (UPGMA) clustering of 
Nei’s unbiased (Nei, 1978) genetic distances between samples pooled into spring groups. D. globosa Cala 
(D24) and D. harrisi H1 and H3 samples have been treated separately, as suggested by inspection of theif 
genetic frequencies. 
524 population has been sufficiently isolated from D. globosa populations for long enough to evolve 
large allelic frequency differences and, in at least this one example, novel allozymes. This population 
has the shell features of D. harrisi (Fig. 3E,H), there being no significant (P«0.01) differences in 
shell dimensions and ratios. However, members of this sample tend to fall in the overlap zone 
between the two species (Fig. 22B). 
Figure 23 shows that the distribution of genetic variation in Dalhousia is not random. The genetic 
distance between populations pooled in spring groups is generally concordant with the degree of 
