Anderson: Systematics of the North American menhadens in the genus Brevoortia 



373 



Table 3 



Genetic diversity estimates over four nuclear loci (AF49462, AF39658, AF39657, and AF39661I and the mtDNA control region 

 locus, for Atlantic menhaden iBrevoortia tyranniis). Gulf menhaden ^B. patroniis), flnescale menhaden (B. gunteri), and yellowfin 

 menhaden (B. smithi). The diversity estimates include allelic diversity (/;. alleles/locus) at each microsatellite locus and overall 

 (k ), multilocus expected heterozygosity (H^,), relative effective population size estimated from multi-locus heterozygosity ( Of), the 

 95% confidence range of mtDNA nucleotide diversity i,t), and the 95% confidence range of mtDNA haplotype diversity (h). Sample 

 sizes were equal (;! = 39) in all comparisons unless otherwise noted. 



'Allelic counts for B. patronus are different from those presented in Table 1 because fewer individuals were used to account for smaller sample 

 sizes in the three remaining species. 



B. tyrannus, to 0.413 in B. gunteri and 0.370 

 in B. smithi. This disparity is due to near fixa- 

 tion of alleles in both small-scaled species at 

 a single locus which is highly polymorphic in 

 both large-scaled species (AF39657), but also 

 reflects decreased variability at all marker loci. 

 As a result, the estimates of Op. in large-scaled 

 species were four to five times larger than those 

 for small-scaled species. 



Sequencing data set 



The mtDNA sequencing data set indicates an 

 enormous amount of genetic variation in the 

 control region of menhaden (Table 3), although 

 this variation was not evenly distributed across 

 the entire alignment. In particular, regions 

 of sequence conservation in the data set were 

 directly adjacent to highly degenerate regions 

 more typical of the mitochondrial control region 

 of clupeids (Grant et al., 1998). Over a total 

 dataset of 360 bp, 149 sites were polymorphic, 

 and pairwise sequence comparisons resulted in 

 an average of 28.7 nucleotide differences among 

 haplotypes. Of 113 individuals assayed, 106 

 haplotypes were identified in the four species. 

 Despite this high level of sequence divergence, 

 only three single-base deletions were detected 

 in the multiple alignment of 113 individuals 

 (deletions were treated as missing data). The 

 control region of menhaden is A-T rich (contains 

 greater than 50% adenine and thymine bases), 

 with averaged base frequencies of A = 0.269, 

 T = 0.487, C (cytosine) = 0.156, and G (guanine) = 

 0.167, and with no evidence for heterogeneity of 

 base frequencies among taxa (x^=59.40, P=1.00). 



Large-scaled menhaden 



B. patrunus 



B. tM'aiimi.s 



B. smithi 



•- Small-scaled menhaden 



B. gunteri 



F,=005 



Figure 2 



Neighbor-joining dendrogram of populations (n = 20, in each 

 population) of Gulf menhaden (Brevoortia patronus), Atlantic 

 menhaden (B. tyrannus), finescale menhaden (B. gunteri), and 

 yellowfin menhaden (B. smithi). The distance metric used for 

 neighbor-joining was F^, (Weir and Cockerham, 1984), which 

 is the estimated proportion of genetic variance that is due to 

 between-population effects 



