22 
Fishery Bulletin 107(1) 
and silver seatrout, which have sympatric distributions 
in the GOM. 
This finding supports the monophyly of an assem- 
blage that includes sand seatrout and gray weakfish 
and may indicate that silver seatrout diverged from 
this group before the sea level changes of the last gla- 
cial maximum. The current data indicate complete di- 
vergence in two morphological characters and a single 
genetic (mtDNA) locus between sand and silver seat- 
rout. In contrast, the morphological data of Aguirre and 
Shervette (2005) indicate a sister-species relationship 
between sand seatrout and weakfish. Interestingly, the 
silver seatrout is the only one of the three species that 
is not partially estuarine-dependent, indicating that 
estuarine independence may have evolved after the spe- 
ciation process. Furthermore, because silver seatrout 
are not tied to shallow estuarine waters, they may have 
eluded the significant vicariance effects (that is, genetic 
divergence caused by the appearance of a transient or 
permanent boundary) caused by sea level shifts during 
periods of glacial advance. However, caution must be 
used in interpreting genetic data in light of contem- 
porary distribution range because extant distributions 
are not necessarily good indicators of geographic rang- 
es at the time of divergence (Losos and Glor, 2003). 
Whatever the case, trophic partitioning between the 
two species likely contributes to the heterogeneous 
offshore distribution of sand seatrout, in contrast to 
the relatively consistent offshore distribution of silver 
seatrout (Ginsberg, 1931; Byers, 1981; McDonald et al., 
2009). These data indicate that partitioning may also 
play a role in the maintenance of reproductive barri- 
ers between species, resulting in distinctive genetic 
profiles, and little evidence of evolutionary association 
after speciation. 
Acknowledgments 
The fisheries monitoring staff at the Galveston Bay Field 
Office, Texas Parks and Wildlife (TPW), including ecosys- 
tem leaders R. Hensley and B. Balboa, were responsible 
for sample collection. Samples were collected during TPW 
routine monitoring, which is funded by Federal Aid in 
Sportfish Restoration Grant (FRM-34). Assistance during 
sample processing was provided by M. Jesberg, A. Mione, 
E. Young, and R. Vickers. Improvements to the first 
draft were provided by M. Fisher and B. Bumguardner 
(TPW), and three anonymous reviewers. This research 
project was funded in part by dedicated funds from a 
Federal Aid in Sportfish Restoration Grant (F-158-R). 
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