Merkouris et al.: Genetic diversity in Chionoecetes bairdi and C. opilio 
533 
2*, ADA-3*, ALAT*, CBYR*, (5GALA*, GAPDH*, 
pGLUA*, G3PDH-1*, G3PDH-2*, GPI-A1*, IDHP-1*, 
MDH-A1 *, MDH-A2*, MEP-1*, MPI*, PEPA*, PEPD- 
2*, PGDH*, PGM-1*, PROT-1*, PROT-2*, PROT-3* , 
and TPI-1*, were scored in all C. bairdi and C. opilio 
populations analyzed; 16 loci, AAT-1*, AAT-2*, AH - 
3*, ALAT*, CBYR*, G3PDH-1*, G3PDH-2*, GPI-A1*, 
IDHP-1*, MDH-A1* , MDH-A2*, PEPA*, PGDH*, 
PGM-1*, PROT-3*, and TPI-1*, were polymorphic in 
at least one population of either species. Eleven loci, 
ADA-1*, ADA-2*, ADA-3*, pGALA*, GAPDH*, 
pGLUA*, MEP-1*, MPI*, PEPD-2*, PROT-1*, and 
PROT-2*, were monomorphic for the identical allele. 
Significant differences (P<0. 01) between the two spe- 
cies were detected at eight loci, AH-3*, G3PDH-1*, 
GPI-A1*, IDHP-1*, MDH-A1 *, PEPA*, PGDH*, and 
PROT-3*. Two loci, AH-3* and PROT-3*, were par- 
ticularly informative with nearly fixed differences for 
alternate alleles (Table 3). In addition, with the ex- 
ception of C. opilio from the Pribilof Island area col- 
lections, C. opilio expressed only the IDHP-1* 100 
allele, whereas C. bairdi were highly variable. Sev- 
eral low-frequency variants (P<0.05) also contributed 
to the overall differences between the species. Numer- 
ous low-frequency alleles detected in only Bering Sea 
collections of C. bairdi were also detected in Alaskan 
C. opilio collections, including the following: AAT-2 *69, 
CBYR* 117, G3PDH-2*86, GPI-A1*55, MDH-A1*79, 
PGM-1*103, and PROT-3*88. Also, a rare allele, 
PGDH* 112, was detected only in Bristol Bay C. bairdi 
and in Pribilof Island and Atlantic Ocean C. opilio. 
Multilocus variation between species was estimated 
by genetic-distance measures. Between-species ge- 
netic-distance measures ranged from 0.222 to 0.251. 
The largest genetic distance was between Atlantic C. 
opilio and two northern Gulf of Alaska C. bairdi popu- 
lations, those of Kachemak Bay and Montague Strait. 
The smallest between-species genetic distance was that 
for Pribilof Island and Bering Sea C. opilio compared 
with that for Bering Sea and Pribilof Island C. bairdi. 
Table 5 
Hierarchical log-likelihood analysis for Chionoecetes opilio. 
Source 
df 
Overall 
Total 
96 
121.93* 
Among 
32 
41.63 
Within 
64 
80.30 
Bering Sea 
64 
80.30 
Atlantic Ocean 
0 
0.00 
* Significant value (P< 0.05 ) 
Chiocoetes bairdi x C. opilio hybrids 
Hybrids between C. bairdi and C. opilio crabs in the 
Bering Sea have been identified morphologically and 
genetically (Karinen and Hoopes, 1971; Johnson, 
1976; Grant et al., 1978; Hoopes et al. 1 ). Several col- 
lections in our study had allele frequencies suggest- 
ing either low levels of introgression between the 
species or the inclusion of hybrid or backcross indi- 
viduals in the collection. For example, low frequen- 
cies of PROT-3*100 were observed in C. bairdi crabs 
from Bristol Bay, the Bering Sea, and the Pribilof 
Islands. PROT-3* 100 was not observed in C. bairdi 
from non-Bering Sea collections. Similarly, PROT- 
3*88 was observed in C. opilio collections from the 
Bering Sea, St. Matthew Island, and the Pribilof Is- 
lands, and low frequencies of IDHP-1*81 and *119 
were observed in Pribilof Island C. opilio collections; 
these alleles were not observed in C. opilio collected 
from the Atlantic Ocean. 
Discussion 
Allozyme electrophoresis techniques have been used 
extensively to describe evolutionary relationships 
within genera of decapod crustaceans (Bert, 1986; 
Bert and Harrison, 1988; Busack, 1989; Abdullah and 
Shukor, 1993); however, these techniques have gen- 
erally revealed very low levels of intraspecific genetic 
variation (Nelson and Hedgecock, 1980; Smith et al., 
1980; Busack, 1988; Seeb et al., 1990b). Exceptions 
to this generalization are found in species that occur 
over broad geographic areas or in widely different 
environments (Nelson and Hedgecock, 1980; Mulley 
and Latter, 1981; Kartavtsev et al., 1991). Signifi- 
cant population heterogeneity has been found in spe- 
cies that exhibit highly specialized life history at- 
tributes (Stevens, 1991) and in some freshwater spe- 
cies (Macaranas et al., 1995; Fetzner et al., 1997). 
Within a marine species, Seeb et al. ( 1990a) discrimi- 
nated populations of red king crab from major geo- 
graphic areas of the Gulf of Alaska and Bering Sea. 
Allozyme techniques have also been used to examine 
seasonal variability of decapod larval, megalopal, and 
adult allelic frequencies (Kordos and Burton, 1993). 
Davidson et al. (1985) examined population struc- 
ture in North Atlantic C. opilio using allozymes and 
interpreted their observed esterase polymorphisms 
as phenotypic expressions of probable genotypic dif- 
ferences. However, we feel caution should be used in 
interpreting their data until genetic transmission of 
these markers can be shown by inheritance studies 
because we were unable to interpret the genetic ba- 
sis of observed esterase activity. 
