FISHERY BULLETIN: VOL. 82, NO. 4 



marginatus is homologous to this GPI locus of 

 other decapods. 



Mannosephosphate Isomerase (MPI.) Man- 

 nosephosphate isomerase is polymorphic in many 

 crustaceans and behaves as a monomeric protein. 

 The observed MPI phenotypes in P. marginatus 

 are consistent with this presumed subunit struc- 

 ture (Fig. 2). Further, a more detailed analysis of 

 the MPI variation in P. marginatus indicates that 

 the MPI locus in this species is sex-linked and 

 that, although there are three alleles segregating 

 in the species, males always have at least one slow 

 allele while females only very rarely carry this 

 same allele (Shaklee 1983). Because of this restric- 

 tion on segregation, the slow allele was pooled 

 with the medium (100) allele (Table 2) for the 

 statistical analyses of population structure. 



Peptidases (PEP). Like esterases, the pep- 

 tidases represent a family of enzymes sharing 

 similar catalytic activities. However, unlike the 

 esterases, there are a relatively small number 

 of different peptidases, and they exhibit differen- 

 tial and somewhat characteristic substrate 

 specificities (Frick 1983). Peptidases have been 

 studied in both P. argus and P. cygnus. Hanley 

 (1980) reported that two peptidases (using 

 leucylglycylglycine and leucyltyrosine as sub- 

 strates) are monomorphic in P. cygnus. Menzies 

 and Kerrigan (1979a) and Menzies (1981) reported 

 two monomorphic and three polymorphic pep- 

 tidases in P. argus. One of these variable pep- 

 tidases is a prolidase (stained with leucylproline 

 or phenylalanylproline) which appears to be a 

 dimer and exhibits three alleles. The other two 

 variable peptidases (stained with leucylglycine or 

 phenylalanyltyrosine) are apparently monomers. 

 Whether or not the two variable peptidases in P. 

 marginatus (which behave as monomers, Fig. 2) 

 are homologous to any of those described in P. 

 argus is not clear at this point. 



Phosphoglucomutase (PGM). Essentially all 

 species of decapod crustaceans exhibit one PGM in 

 muscle. The enzyme is reported to be monomeric 

 and it exhibits Mendelian inheritance in H. 

 americanus (Hedgecock et al. 1975). The PGM of P. 

 marginatus appears to be homologous to this PGM 

 of other decapods. 



Despite that direct inheritance testing of the 

 presumed genetic variation observed in the 

 Hawaiian P. marginatus was not attempted, the 

 general agreement between the observed isozyme 

 patterns and those reported for other decapod 

 crustaceans, the data indicating the genetic 



basis for variation in EST, GPI, MPI, and PGM in 

 other decapods, and the general agreement in P. 

 marginatus between observed genotypic distribu- 

 tions and those expected assuming Hardy- 

 Weinberg equilibrium, strongly support the as- 

 sumption that the observed variation in the 

 Hawaiian spiny lobster is under direct genetic 

 control. 



The present study of P. marginatus has revealed 

 electrophoretic variation encoded by 7 gene loci. 

 However, in spite of the fact that over 1,800 lobsters 

 from five localities were analyzed, none of the 

 statistical tests of stock structure provided con- 

 vincing evidence of subpopulation differentiation 

 within the Hawaiian Archipelago. Indeed, the 

 overall impression is one of remarkable genetic 

 uniformity throughout the range of this species. 

 This outcome is perhaps not too surprising, since 

 levels of detectable genetic variation are quite low 

 in P. marginatus: hence, a robust test of stock 

 structure using electrophoresis is difficult at best 

 and requires very large sample sizes. Additionally, 

 assuming that this species has larval life history 

 characteristics similar to those of other species in 

 the family, namely a series of planktonic phyl- 

 losoma stages lasting from 6 to 12 mo, dispersal 

 and mixing of larvae throughout the Hawaiian 

 Archipelago might be expected. However, this 

 same current-driven transport and dispersal 

 might also be expected to disperse larvae to other 

 Pacific island groups near Hawaii (e.g., Johnston 

 Atoll, the Line Islands, the Marquesas, the 

 Tuamotus, the Gilbert Islands, the Marshall Is- 

 lands, etc.). It is, therefore, somewhat of a paradox 

 that, with the exception of one report of a single 

 individual that was collected at Johnston Atoll 

 (Brock 1973), P. marginatus is only found in the 

 Hawaiian Islands. 



The lack of demonstrable subpopulation dif- 

 ferentiation in P. marginatus is not unusual for a 

 decapod crustacean. Studies of other decapods 

 have also generally failed to reveal stock 

 heterogeneity (Lester 1979; Smith et al. 1980). 

 Even in those cases where some genetic differ- 

 ences among stocks have been reported, the 

 amount of differentiation is almost always very 

 small (Tracey et al. 1975; Hanley 1980; Mulley and 

 Latter 1981a, b). The only notable exception is the 

 case of P. argus which exhibits substantial varia- 

 tion throughout the Caribbean (Menzies and Ker- 

 rigan 1979a; Menzies 1981). Hence, the Hawaiian 

 spiny lobster fits the common decapod pattern of 

 low heterozygosity and little subpopulation dif- 

 ferentiation. At this point, all indications suggest 



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