122 
M.R. Yardin, B.J. Richardson 
Mackie 1993, Grant-Mackie and Cook 1990). A. 
trapezia apparently sporadically colonized New 
Zealand during the Late Pliestocene period. 
The distribution of A. trapezia is now restricted to 
the eastern coast of Australia with a second, 
disjunct, southwestern Australian population. 
Questions have been raised as to whether the 
southwestern Australian population of A. trapezia 
has diverged during the separation time from the 
eastern populations. Speciation depends not only 
upon the spatial duration of the geographic barrier, 
changes in climate and related fauna and flora but 
also upon the characteristics of the organism itself. 
These include habitat selection, vagility and means 
of reproduction and dispersal. The phenomenon of 
disjunction has aroused considerable interest in 
studies of speciation and has been studied in great 
detail by classical geneticists (e.g., Mayr 1942,1954, 
1963; Huxley 1942). Even though it is generally 
accepted that geographic isolation favours 
allopatric speciation, other factors such as special 
ecological features are also important (e.g., Johnson 
and Black 1990). 
The aim of the study was to determine the level 
of genetic divergence and hence the specific status 
of the geographically disjunct southwestern 
Australian population of A. trapezia relative to the 
east Australian populations. 
MATERIALS AND METHODS 
Seven individuals of Anadara trapezia were 
obtained from Oyster Harbour, near Albany, 
Western Australia. To examine the degree of 
genetic divergence in this population, the sample 
set from Oyster Harbour (35°30'S, 118°E) was 
compared with two sample sets, each of seven 
specimens, one from Corinella, Western Port Bay 
Victoria (38°22'S and 145°34'E), and the other from 
Fingal Bay, Tweed Heads estuary, northern New 
South Wales (28°16'S and 153°35'E). These two 
samples were taken as representatives of the 
southern and northern sections of the east coast 
population respectively. 
As discussed in Richardson et al. (1986), the 
sample size needed for the electrophoretic 
detection of a suspected cryptic species is a 
minimum of five individuals. Since the detection of 
cryptic species relies heavily upon finding fixed 
differences, the method depends upon the number 
Table 1 Electrophoretic conditions and staining methods. * Indicates polymorphic locus. Locus was considered 
polymorphic if more than one allele was detected. 
Enzyme 
Abbreviation 
E.C. 
Number 
Buffer 
system 
Number 
of loci 
Alanopine dehydrogenase 
ALPD* 
1.5.1.17 
A 
i 
Enolase 
ENOL 
4.2.1.11 
B 
i 
Glutamate dehydrogenase 
GDH 
1.4.1.3 
A 
i 
Isocitrate dehydrogenase 
IDH* 
1.1.1.42 
B 
i 
Glucose-6-phosphate dehydrogenase 
G6PD 
1.1.1.49 
A 
i 
Sorbitol dehydrogenase 
SORDH 
1.1.1.14 
A 
i 
Glucose dehydrogenase 
GLDH 
1.1.1.118 
A 
i 
6-phospho gluconate dehydrogenase 
6-PGD 
1.1.1.44 
A 
i 
Malic enzyme 
ME* 
1.1.1.40 
A 
i 
Fumarate hydratase 
FUM 
4.2.1.2 
A 
i 
Strombine dehydrogenase 
STR 
1.5.1.X 
A 
i 
Aconitate hydratase 
ACON 
4.2.1.3 
A 
i 
Esterase methylumbelliferyl butyrate 
EST 
3.1.1.1 
B 
i 
Alanine amino transferase 
GPT 1 
GPT 2 
2.6.1.2 
B 
2 
Malate dehydrogenase 
MDH 1* 
MDH 2* 
1.1.1.37 
A 
2 
Octopine dehydrogenase 
ODH* 
1.5.1.11 
A 
1 
Cytosol amino peptidase/leucine amino peptidase 
CAP* 
Formerly LAP* 
3.4.11.1 
A 
1 
Mannose phosphate isomerase 
MPI* 
5.3.1.8 
C 
1 
Phosphoglucomutase 
PGM* 
2.7.5.1 
A 
1 
Glucose phosphate isomerase 
GP1* 
5.3.1.9 
A 
1 
Arginine kinase 
AK 
2.7.3.3 
A 
1 
Aspartate amino transferase 
GOT 1 
GOT 2 
2.6.1.1 
A 
2 
Pyruvate kinase 
PYR 
2.7.1.40 
B 
1 
Guanine deaminase 
GDA* 
3.5.4.3 
D 
1 
