Graves et al ' Biochemical genetics of Paralabrax 



65 



Discussion 



The results of the electrophoretic and mtDN A analyses 

 are similar in several respects. First, the absolute level 

 of genetic differentiation between the Paralabrax 

 species is relatively small and is consistent with values 

 typically found between other closely related organisms 

 (Avise and Aquadro 1982, Ferris and Berg 1987). Sec- 

 ond, the comparison of P. maculatofasciatus and 

 P. nebulifer yields the smallest genetic distance of the 

 three pairwise comparisons. 



A major focus of the electrophoretic and mtDNA 

 analyses was to find a biochemical character which 

 would unambiguously differentiate the early-life- 

 history stages of the three Paralabrax species found 

 in southern California coastal waters. The electro- 

 phoretic investigation revealed several apparently fixed 

 allelic differences between any two of the three species 

 and demonstrated that a screening of a minimum of 

 two electrophoretic loci will result in a positive specific 

 identification. This methodology can be used to iden- 

 tify late larvae, juveniles, or adults in which there is 

 sufficient tissue (or enzyme activity) to survey two or 

 more loci. However, it was not always possible to score 

 the diagnostic loci in Paralabrax eggs and larvae 

 smaller than 10 mm total length. Although it may have 

 been possible to improve the resolution of the electro- 

 phoretic techniques, we chose to rely upon mtDNA 

 restriction fragment differences to identify Paralabrax 

 eggs and early larvae. 



The restriction endonuclease analysis of Paralabrax 

 mtDNA, like the electrophoretic survey, demonstrated 

 considerable genetic differentiation among the three 

 species. Several restriction endonucleases were each 

 capable of distinguishing the three species of basses. 

 Furthermore, the mtDNA analysis not only worked 

 with relatively large adult tissue samples, but with 

 quantities as small as an individual egg. Consequent- 

 ly, the mtDNA analysis is the method of choice for the 

 identification of Paralabrax early-life-history stages. 



Several ecological and assessment studies involving 

 Paralabrax eggs and early larvae have not been possi- 

 ble because of an inability to specifically identify the 

 early-life-history forms. The mtDNA isolation and 

 analysis techniques presented in this paper will facili- 

 tate such studies. Furthermore, because the methods 

 work with ethanol-preserved as well as fresh speci- 

 mens, there is no need to separate Paralabrax eggs 

 and larvae from a fresh plankton tow while at sea. 



Acl<nowledgments 



Robert Lavenberg kindly provided the Paralabrax 

 eggs and larvae and reviewed a copy of this manu- 

 script. This study was supported by grant F#50-R from 

 the California Department of Fish and Game. 



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