NOTE Blandon et al.: Genetic population structure of Paralichthys lethostigmci 
675 
Table 2 
Assignment test outcomes. Values indicate frequency of assignment of individuals from a collection locality (rows) to the locality to 
which it is most similar (columns). Numbers on the diagonal indicate correct assignments. The “East” category combines collections 
from North Carolina to Sabine Lake, Texas, and the “West” category combines Texas sites from Galveston Bay to Laguna Madre. 
NC = Core Sound, North Carolina; STA = off St. Augustine, Florida; ALA = Mobile Bay, Alabama; MIS = off Biloxi, Mississippi; 
SAB = Sabine Lake, Texas; GAL = Galveston Bay, Texas; MAT = Matagorda Bay, Texas; LM = Laguna Madre, Texas. 
Assigned to 
From 
NC 
STA 
ALA 
MIS 
SAB 
GAL 
MAT 
LM 
NC 
29 
0 
4 
0 
2 
0 
0 
0 
STA 
13 
0 
5 
1 
0 
1 
0 
0 
ALA 
8 
0 
6 
3 
0 
0 
0 
0 
MIS 
4 
1 
0 
4 
3 
1 
0 
0 
SAB 
15 
1 
4 
2 
10 
5 
0 
0 
GAL 
9 
0 
2 
1 
2 
22 
1 
0 
MAT 
8 
0 
6 
6 
1 
0 
14 
25 
LM 
7 
0 
4 
0 
0 
1 
3 
19 
East 
158 
1 
West 
33 
61 
MAT 
m 
Figure 2 
Unrooted neighbor-joining tree depicting the underlying structure 
found in the pairwise Cavalh-Sforza and Edwards chord distance 
matrix for eight collections of southern flounder. Numbers indicate 
bootstrap support in 1000 replications and white ellipses indicate 
nodes with bootstrap support below 50%. LLM = Lower Laguna 
Madre; MAT = Matagorda Bay; GAL = Galveston Bay; SAB = 
Sabine Lake; MS = Mississippi; AL = Alabama; STA = St. Augus- 
tine, Florida; NC = North Carolina. 
tistically significant correlations were observed be- 
tween chord distances and geographic distances 
h-0.416, £=1.549, P=0.06). 
Discussion 
Genetic differentiation was not extensive over most 
of the range of P. lethostigmci examined in this 
study. Samples collected from Core Sound in North 
Carolina to Sabine Lake on the upper Texas coast 
were genetically similar. However, a discontinuity 
in allele frequencies was identified on the Texas 
coast between Galveston and Matagorda Bays. In 
addition, statistically significant dines in allele fre- 
quencies at the G6PDH-2 * locus and in average 
individual heterozygosity were observed across the 
Gulf of Mexico. These observations do not suggest 
the occurrence of independent stocks of southern 
flounder in the Gulf of Mexico but do support 
the hypothesis that genetic structuring is present. 
Southern flounder samples collected off St. Augus- 
tine, FL, and off North Carolina cluster with sam- 
ples in the Gulf of Mexico from Galveston Bay, 
Texas, eastward, despite a modern-era distribu- 
tional gap that encompasses the southern reaches 
of Florida from the Loxahatchee River on the Atlan- 
tic Coast to the Caloosatchee Estuary on the Gulf 
Coast (NOAA 5 ). This apparent gap may not repre- 
sent an effective barrier to gene flow or may be 
of such recent origin that differentiation has been 
minimal. It is also possible that differences existed 
that were undetected by techniques used in our study. 
Significant correlation between genetic and geographic 
distance was not found, lending no support to application 
of the isolation by distance model (Wright, 1943) to pop- 
5 NOAA. 1985. Gulf of Mexico coastal and ocean zones stra- 
tegic assessment:data atlas, 188 p. Strat. Assess. Branch, 
Ocean Assess. Div., Off. Oceanography Mar. Assess., Nat. Ocean 
Serv. and the Southeast Fish. Center, NMFS, NOAA, U.S. Dep. 
Commer., 75 Virginia Beach Dr, Miami, FL 33149. 
