CRAWFORD ET AL : STOCK IDENTIFICATION OF WEAKFISH 



Malate dehydrogenase 



Mdh-1 



Mdh-2 



Mdh-3 



Origin 



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 <P_ <P_ 0_ (P^ o 



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Mdh-2 

 genotypes 



Figure 2.— Diagram of observed isozyme pattern for Mdh. The darlc bands are pro- 

 tein products of presumptive loci and the lighter bands are heteropolymers formed 

 from among the products of different loci. 



localities that significantly deviated from HWE 

 caused the chi-square values to become nonsignifi- 

 cant. At a frequency of 0.149 (if assumed through- 

 out the sampling range) the expected number of in- 

 dividuals homozygous for the null allele among all 

 the samples is 20, yet only two were found. 



Our analyses indicated that there were no signif- 

 icant differences of allelic frequencies among sam- 

 pling locations or among geographic regions (Table 

 2). The value of F,^ was 0.046 and Nei's (1972) 

 genetic distances were <0.003. No significant dif- 

 ferences in allelic frequencies between juveniles 

 (mean total length = 113 mm) and adults (mean total 

 length = 310 mm) existed (Pgd: x' = 2.622, P > 

 0.05, df = 1; Mdh-2: x^ = 0.001, P > 0.05, df = 1). 



Comparisons between male and female fish in- 

 dicated significantly different allozyme frequencies 

 for Mdh-2 but not for Pgd. The frequency of the 

 common allele (100) at the Mdh-2 locus was 0.518 

 + 0.033 (SE) for 114 males and 0.637 ± 0.035 (SE) 

 for 95 females, and these frequencies were signifi- 

 cantly different (x' = 6.024, P < 0.05, df = 1). No 

 differences were found at the Pgd locus (x" = 

 1.785, P > 0.10, df = 1). 



DISCUSSION 



Our study of allelic frequencies from populations 

 of C. regalis along the east coast between Cape Cod, 

 MA and Cape Hatteras, NC identified no statistical- 

 ly distinguishable differences. Nei's (1972) genetic 

 distances are quite small and the F^f value (0.046) 

 is low; both indicate little genetic variation among 

 the populations. Nonsignificant allelic frequency 

 comparisons among geographic locations and size/ 

 age classes were consistent with population homo- 

 geneity. A comparison of allelic frequencies at the 

 Mdh-2 locus showed a significant difference between 

 sexes. We are unable to explain this difference and 

 cannot discount sex linkage or sexual selection as 

 possible causes. Alternatively, with the numerous 

 chi-square tests used in the analyses a Type II 

 statistical error may have occurred. 



Sample populations at several locations showed 

 a heterozygote deficiency at Mdh-2 causing devia- 

 tions from Hardy-Weinberg equilibrium. Several 

 factors may cause heterozygote deficiencies (e.g., 

 inbreeding, Wahlund effect, selection against het- 

 erozygotes, scoring biases, and null alleles; Speiss 



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