with Yates correction for small sample sizes (Sokal 

 and Rohlf 1969). Nei's (1978) measure of genetic 

 distance for small sample sizes was calculated be- 

 tween the two groups. 



Results and Discussions 



Data were collected from 22 enzyme systems en- 

 coding the following 32 presumed loci (polymorphic 

 loci having one or more variant alleles are indicated 

 by *): AAT*, ACP-1, ACP-2*, ADA*, ADH*, ALD, 

 G3P-1*, G3P-2, CK-1, CK-2, EST, GAP-1*, GAP-2, 

 GL-1, GL-2, IDH*, LDH-1*, LDH-2, LDH-3, LGG*, 

 MDH-1, MDH-2, MDH-3, ME, PGD*, PGM-1, 

 PGM-2, GPI-1, GPI-2*, PGK*, MPI, SOD. 



Allelic distributions for the 13 polymorphic loci 

 indicate considerable similarity for most of the 

 systems but some distinct differences as well, based 

 on the contingency analysis (Table 2). The nonsig- 

 nificant differences observed at nine of the loci are 

 not highly informative given the limited number of 

 individuals that were sampled. 



However, the differences that were statistically sig- 

 nificant provide considerable information. The most 

 striking difference is at the ADH locus, where no 

 alleles were shared between the 12 arrowtooth and 

 the 10 Kamchatka flounders. These data alone con- 

 firm the genetic distinctness of the two types. The 

 allelic distribution between the two forms is almost 

 as distinct at the GAP-1 locus; a lesser, but signifi- 

 cant difference also exists at the ACP-2 locus. Gel 

 banding patterns observed for these three loci are 

 shown in Figure 1. 



Not surprisingly, the genotypic frequencies at the 

 ADH and GAP-1 loci also deviated significantly (P 

 < 0.001) from the ratios of a binomial expansion of 

 allelic frequencies (Hardy-Weinberg equilibrium ex- 

 pected in a single, randomly mating population). This 

 difference resulted from excesses of homozygous and 

 deficits of heterozygous classes, a situation expected 

 in population mixtures (i.e., the Wahlund effect, see 

 Futuyma 1979). 



The distinct genotypic distribution of the two 

 forms at the ADH and GAP-1 loci, coupled with their 

 sympatric occurrence and subtle but consistent mor- 

 phological identities, support their present tax- 

 onomic status as distinct congeneric species. How- 

 ever, the value of genetic distance observed, 0.052, 

 is rather low for distinct species suggesting recent 

 speciation (Avise 1976). 



Recent genetic studies of two other pleuronectid 

 species sampled from the same geographic region 

 indicate only conspecific variation. The Alaska Pen- 

 insula separates two population groups of yellowfin 



sole, Limanda aspera, at a mean genetic distance 

 of 0.005 (Grant et al. 1983). No significant differences 

 of allelic frequencies were detected in Pacific halibut, 

 Hippoglossus stenolepis, sampled in the Bering Sea 

 and the North Pacific Ocean (Grant et al. 1984). 

 These various outcomes among confamilial group- 

 ings undoubtedly reflect the past and present actions 

 of numerous variables; two major factors are differ- 

 ing capabilities for gene flow based on distinct life 

 history patterns, and differing times and degrees of 

 isolation imposed by glaciation events within the past 

 2 million years (discussed by Grant and Utter 1984). 

 Finally, the possibility of hybridization and intro- 

 gression between the two species of Atheresthes 

 should be examined through more extensive sam- 

 pling of these two forms over a broader geographic 

 range The distinct distribution of ADH alleles ex- 

 cluded a hybrid origin of any individuals in this study. 



Table 2. — Observed number and (in parentheses) within group fre- 

 quency of alleles of 13 polymorphic loci in samples of arrowtooth 

 and Kamchatka flounder. 



'Contingency tests of allelic frequencies using the G-statistic with Yates cor- 

 rection for small sample sizes, assuming all samples drawn from the same 

 population; ns = not significant. 



2 Protein subunit structure based on observed banding patterns of variants; 

 m = monomer, d = dimer, t = tetramer. 



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