SHAKLEE and SAMOLLOW: GENETIC VARIATION IN A DEEPWATER SNAPPER 



Hawaiian Islands. Absolutely no evidence of mul- 

 tiple stocks was found. 



DISCUSSION 



Genetic Inferences 



Because it was not possible in the present study 

 to verify the Mendelian nature of the observed 

 variation in enzyme phenotypes in Pristipomoides 

 filamentosus by direct genetic tests, such a genetic 

 basis can only be inferred from the results of the x 2 

 goodness-of-fit tests (to Hardy-Weinberg expecta- 

 tions) and by comparison of the snapper data with 

 genetic (Purdom et al. 1976; May et al. 1979; 

 Kornfield et al. 1981), molecular (Darnall and 

 Klotz 1975; Mo et al. 1975), and electrophoretic 

 data (Engel et al. 1971) for these same enzymes in 

 other fish species. The genetic and molecular bases 

 of four of the enzymes scored for variation in P. 

 filamentosus have been well documented in other 

 fish species. For three of these (ADH, GPI, and 

 IDDH ) the banding patterns observed in presumed 

 heterozygote snappers were entirely consistent 

 with expectations from other studies. However, the 

 results for two enzymes require additional 

 comment. 



Lactate Dehydrogenase-C 



Three distinct Ldh loci characterize diploid 

 bony fishes (Markert et al. 1975). The Ldh-C locus 

 typically encodes the eye-specific LDH isozyme 

 ( Whitt 1969, 1970; Shaklee et al. 1973), but in some 

 groups it encodes an isozyme predominant in liver 

 (Sensabaugh and Kaplan 1972; Shaklee et al. 

 1973). Both the eye-specific and the liver- 

 predominant LDH isozymes have been charac- 

 terized biochemically (Whitt 1970; Sensabaugh 

 and Kaplan 1972). Electrophoretic variants of the 

 eye-specific LDH encoded at the Ldh-C locus have 

 been shown to be inherited in Mendelian fashion 

 in freshwater sunfish (Whitt et al. 1971) and 

 poeciliids (Leslie and Vrijenhoek 1977; Morizot 

 and Siciliano 1979). The Ldh-C locus has been 

 reported to be variable in numerous species. In 

 essentially all of these cases, the isozyme pattern 

 of the heterozygote has been difficult to resolve 

 into the expected five isozymes, rather it typically 

 appears as a smear of LDH activity extending 

 from the region of the slow allele homozygote to 

 the region of the fast allele homozygote. The pat- 

 tern of LDH-C variation in P. filamentosus shown 

 in Figure 1 is similar to that reported for these 



other species. Although we were unable to resolve 

 the theoretically predicted five C subunit- 

 containing bands in presumed heterozygotes, 

 their status as heterozygotes seems secure since 

 these individuals exhibited two bands at the posi- 

 tion of the B 3 Ci heterotetrameric isozyme (one 

 having the same mobility as the single slow B 3 C? 



heterotetramer in the slow homozygotes and one 

 having the same mobility as the single fast B3C1 

 heterotetramer in the fast homozygotes), just as 

 expected for such heterozygotes (Fig. 1). 



Umbelliferyl Esterase 



Although there are numerous published studies 

 of biochemical properties, genetic variation, and 

 inheritance in fish esterases (Koehn 1969; Fujino 

 1970; Holmes and Whitt 1970; Metcalf et al. 1972; 

 Smith et al. 1978; Leslie and Pontier 1980; Van 

 Beneden et al. 1981), the diversity and hetero- 

 geneity of these enzymes makes the assign- 

 ment of homology difficult. However, since virtu- 

 ally all of the above investigations involved the use 

 of a-naphthyl esters as substrates in the staining 

 reaction and the UMB off! filamentosus (stained 

 using 4-methylumbelliferyl acetate as substrate) 

 does not show detectable activity with a-naphthyl 

 acetate, it seems unlikely that the umbelliferase 

 of the pink snapper is homologus with any of these 

 esterases of other fishes. The only other reports of 

 UMB variation in fish are those of Ward and 

 Beardmore (1977) (= "Est-D") for plaice and of 

 Shaklee et al. (1983) for blue marlin. In both of 

 these species, as in P. filamentosus, UMB exhibits 

 single-banded homozygotes and triple-banded 

 heterozygotes (with isozyme staining intensities 

 in an approximate 1:2:1 ratio as expected for a 

 dimeric protein). These observations and the gen- 

 eral agreement between observed genotype dis- 

 tributions and those expected, assuming Hardy- 

 Weinberg equilibrium, support our genetic in- 

 terpretations of the observed variation in UMB in 

 pink snapper. 



Stock Structure 



Significant differences in allele frequency 

 among fish of differing ages within a single 

 Mendelian population or stock can be due to 1) 

 the differential mortality of certain genotypes 

 (natural selection), 2) genotype-specific differ- 

 ences in catchability (distribution, activity, behav- 

 ior, etc.), 3) chance fluctuations due to nonrep- 

 resentative spawning in different years (genetic 



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