HEDGECOCK ET AL.: GENETIC VARIATION IN PACIFIC SARDINES 



DISCUSSION 



Low Genetic Variation in the Pacific 

 Sardine 



Relative to other clupeoids, the Pacific sar- 

 dine, Sardinops saga.r, is depauperate in allo- 

 zyme variation. Direct comparison with the 

 northern anchovy, Engraulis mordax, in this 

 study shows that the Pacific sardine has less 

 than 259c of the average heterozygosity of the 

 northern anchovy (Table 2A vs. Table 5). The 

 northern anchovy, not the Pacific sardine, ap- 

 pears to have levels of variation typical of those 

 reported in allozyme studies of clupeoids (Table 

 8). Average heterozygosity for 15 marine species 

 of the order Clupeiformes is 7.1% (95% C.L.: 

 6.0-8.2%). The average e.xpected heterozygosity 



for the Pacific sardine, 1.0%, and even the 

 slightly greater heterozygosity found in the 

 Guaymas population sample, 1.6% fall signifi- 

 cantly below the clupeoid distribution {z = 

 -4.02, P < 0.000033 and z = -3.39, P < 0.0003, 

 respectively). 



There is so little variation within and between 

 Pacific sardine populations that it is not possible 

 to test whether distributions of genotypes con- 

 form to the expectations of random mating or 

 whether allelic frequencies are heterogeneous 

 throughout the range of populations sampled. 

 That sardines in widely separated localities have 

 the same rare alleles (Table 2B) suggests 

 strongly, however, that there has been substan- 

 tial gene flow among contemporary populations 

 (Slatkin 1985). 



Table 8. — Allozyme variation reported for marine species of the order Clupeiformes. 



'Polymorphism defined either as Po99 or inclusive of all observed variation 

 ^H, are either unbiased estimtes (Nei 1978) or simple averages. 



=(1) Hedgecock et al, 1988; (2) Fujio and Kato 1979; (3) Grant 1984; (4) Andersson et al. 1981; (5) Kornlield et al. 

 1982; (6) Grant and Utter 1984; (7) Smith and Robertson 1981 ; (8) Daly and Richardson 1980; (9) Grant 1985a. 



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