GRANT ET AL.: POPULATION GENETICS OF YELLOWFIN SOLE 



TABLE 7. — Gene-diversity analysis of yellowfin sole of the North 

 Pacific Ocean and Bering Sea 



frequency differences among the samples from that 

 region. In addition to adult migration, the passive 

 transport of pelagic eggs and larvae may also con- 

 tribute to gene flow between stocks within these 

 two regions. 



In contrast to the genetic homogeneity within these 

 regions, significant allele- frequency differences were 

 detected for the four polymorphic loci between the 

 Bering Sea and the Gulf of Alaska. This genetic sub- 

 division across the Alaska Peninsula was also re- 

 flected in the genetic distances between samples and 

 in the gene-diversity analysis. 



The reason for the observed genetic structure of 

 yellowfin sole populations cannot be due to isolation 

 by distance, because the greatest genetic differences 

 were detected between nearby populations and not 

 between more distantly separated populations. The 

 two major genetic groups most likely reflect past 

 periods of isolation and genetic divergence caused by 

 coastal glaciation during the Pleistocene. The first of 

 four major glacial periods in Alaska began about 2 

 million yr ago and the last major period of glaciation 

 ended only 1 1,000 yr ago (Ericson and Wollin 1964; 

 Pewe and Roger 1972). During most of these periods 

 glacial ice covered the coastline of the Alaska Penin- 

 sula and central Alaska. Since yellowfin sole are 

 rarely found at depths > 100 m (Hart 1973) and since 



juveniles use shallow bays and estuaries as nursery 

 areas, populations would be greatly influenced by 

 coastal glaciation. There are similar genetic sub- 

 divisions across the Alaska Peninsula or across the 

 Bering Sea for Pacific herring, Clupea pallasi (Grant 

 in press); walleye pollock, Theragra chalcogramma 

 (Iwata 1975; Grant and Utter 1980); and Pacific cod, 

 Gadus macrocephalus (Grant et al. 8 ). 



How similar is the genetic population structure of 

 yellowfin sole to that of other flatfishes? Two statis- 

 tics can be used to make this comparison, genetic dis- 

 tance and relative gene diversities. The former 

 statistic cannot be used for most of the available flat- 

 fish data because only a few loci were examined in 

 these studies. The gene- diversity analysis is more 

 appropriate in cases where only a few loci have been 

 examined because the analysis can be computed for 

 each locus. Nonetheless, the best estimates of pop- 

 ulation structure are averages over loci because ran- 

 dom effects can produce different results for 

 different loci, even though each locus experiences the 

 same population events. Caution must be used when 

 comparing the results of these analyses between 

 species because the results depend, in part, on the 

 geographic extent of the study and, hence, on the 

 number of genetic subdivisions included in the data. 

 A summary of all of the available biochemical data for 

 five species of flatfishes is presented in Table 8 in the 

 form of a gene- diversity analysis. 



Thirteen loci (2 polymorphic loci) were examined in 

 Greenland halibut, Reinhardtius hippoglossoides, 

 collected from four coastal areas of eastern Canada 

 and from the Bering Sea (Fairbairn 1981a). If only 

 the Canadian samples are considered, 99.93% of the 

 gene variation was contained within populations, and 



8 Grant,W. S., C.I. Zhang, and T. Kobayashi. 1982. Biochemical 

 genetics of Gadus: II Population structure of Pacific cod (Gadus 

 macrocephalus). Processed rep., 27 p. Northwest and Alaska Fish- 

 eries Center, National Marine Fisheries Service, NOAA, 2725 

 Montlake Blvd. East, Seattle, WA 98112. 



TABLE 8. — Summary of relative gene diversities in five species of flatfishes. 



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