Gold and Richardson: Sciaenops ocellatus from Mosquito Lagoon 



61 



alleles per locus or lower estimates of mean het- 

 erozygosity, or both, than do red drum from the 

 northeastern Gulf and Carolina coast. The differ- 

 ences in genetic variation, however, are non-random 

 across loci. Heterozygosity per locus values among 

 Mosquito Lagoon fish at loci (e.g., ACP-2* , ADA*, 

 ADH*, sAAT-1*, and EST-1*) where alternate alleles 

 occurred at frequencies of five percent or greater 

 were equivalent to values among fish from the 

 northeastern Gulf and Carolina coast (data not 

 shown). Differences in heterozygosity per locus val- 

 ues were observed at loci (e.g., GPI-B *, PEPB* , and 

 PEPD* ) where alleles occurring in a frequency of one 

 to three percent in northeastern Gulf or Carolina coast 

 fish, or both, were not found among Mosquito Lagoon 

 fish (Appendix Table 1). 



Significant heterogeneity (P<0.05) in allele fre- 

 quencies among test groups was found by using the 

 G-test at ADA* (G=33.92, df=22, P=0.004) and sAAT- 

 1* (G=13.59, df=6, P=0.036). Additional G-tests were 

 carried out after pooling alleles whose frequency in 

 any sample was less than 10%. Significant hetero- 

 geneity was again found at ADA* (G=9.62, df=4, 

 P=0.048) and also at PEPB* (G=6.86, df=2, PM3.034). 

 Examination of allele frequencies at ADA*, sAAT-1, 

 and PEPB* did not reveal any striking differences 

 among test groups, suggesting that heterogeneity 

 was due to accumulation of small differences in fre- 

 quencies of rare alleles. At ADA*, for example, the 

 frequency of Allele *115 was higher among Mosquito 

 Lagoon fish and lower among Carolina coast fish; 

 whereas the frequencies of Alleles *90 and *85 were 

 higher among northeastern Gulf fish (Appendix 

 Table 1). At sAAT-1* and PEPB*, slight frequency dif- 

 ferences were apparent for Allele * 110 (higher in 

 Mosquito Lagoon fish) and Allele 115 (higher in 

 northeastern Gulf fish and absent 

 from Mosquito Lagoon fish), re- 

 spectively (Appendix Table 1). The 

 observation that G-test heteroge- 

 neity was due to small, cumula- 

 tive frequency differences was cor- 

 roborated by V-tests where no sig- 

 nificant heterogeneity (P>0.05) in 

 allele frequencies was found at 

 any locus following corrections for 

 multiple tests. 



MtDNA fragment patterns from 

 single digestions with 13 restric- 

 tion enzymes generated 36 com- 

 posite mtDNA haplotypes among 

 fish from Mosquito Lagoon, eleven 

 of which (numbers 114, 134-143) 

 have been found only in Mosquito 

 Lagoon red drum (Appendix Table 



2). Estimates of mtDNA variation (Table 2) indi- 

 cated that nucleon diversity (the probability of any 

 two individuals differing in mtDNA haplotype) was 

 highest in red drum from the northeastern Gulf and 

 lowest in red drum from the Carolina coast; whereas 

 intrapopulational nucleotide sequence diversity (the 

 genetic difference between any two individuals) was 

 greatest among Mosquito Lagoon fish. These esti- 

 mates of mtDNA variation are among the highest 

 reported to date for a non-clupeid, marine fish spe- 

 cies (Richardson and Gold, 1993). 



Highly significant heterogeneity in mtDNA- 

 haplotype frequencies among test groups and be- 

 tween pairwise comparisons of test groups were 

 found in both G-tests and Monte Carlo 

 bootstrapping (Table 3). These results indicate that 

 all three test groups differ significantly from each 

 other. V-tests, carried out on haplotypes found in ten 

 or more individuals (12 haplotypes total), identified 

 six haplotypes (Table 4) that differed significantly 

 among test groups. Genetic distances based on 

 allozymes and mtDNAs (Table 5) indicate that red 

 drum from Mosquito Lagoon are at least as diver- 

 gent genetically from red drum in the northeastern 

 Gulf and Carolina coast as the latter two are from 

 each other. 



Discussion 



Tests of heterogeneity clearly indicate that red drum 

 from Mosquito Lagoon differ genetically from red 

 drum in the northeastern Gulf and along the Caro- 

 lina coast and that at least three subpopulations of 

 red drum occur in U.S. waters. That the genetic 

 differences appear more pronounced in mtDNA than 



