13 
Abstract— The evolutionary asso- 
ciations between closely related fish 
species, both contemporary and his- 
torical, are frequently assessed by 
using molecular markers, such as 
microsatellites. Here, the presence 
and variability of microsatellite loci in 
two closely related species of marine 
fishes, sand seatrout ( Cynoscion are- 
narius) and silver seatrout ( C . nothus), 
are explored by using heterologous 
primers from red drum (Sciaenops 
ocellatus). Data from these loci are 
used in conjunction with morphologi- 
cal characters and mitochondrial DNA 
haplotypes to explore the extent of 
genetic exchange between species off- 
shore of Galveston Bay, TX. Despite 
seasonal overlap in distribution, low 
genetic divergence at microsatellite 
loci, and similar life history param- 
eters of C. arenarius and C. nothus, all 
three data sets indicated that hybrid- 
ization between these species does not 
occur or occurs only rarely and that 
historical admixture in Galveston 
Bay after divergence between these 
species was unlikely. These results 
shed light upon the evolutionary his- 
tory of these fishes and highlight the 
genetic properties of each species that 
are influenced by their life history 
and ecology. 
Manuscript submitted 24 April 2008. 
Manuscript accepted 22 August 2008. 
Fish. Bull. 107:13-23 (2009). 
The views and opinions expressed 
or implied in this article are those 
of the author and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Evolutionary associations between sand seatrout 
( Cynoscion arenarius) and silver seatrout 
(C. nothus ) inferred from morphological characters, 
mitochondrial DNA, and microsateSlite markers 
Joel D. Anderson (contact author ) 1 
Dusty L. McDonald 1 
Glen R. Sutton 2 
William J. Karel 1 
Email address for contact author: JoelAnderson@tpwd.state.tx.us 
1 Perry R. Bass Marine Fisheries Research Station 
Texas Parks and Wildlife Department 
HC02 Box 385, Palacios, Texas 77465 
2 Galveston Bay Field Office 
Texas Parks and Wildlife Department 
1502 FM 517 East, 
Dickinson, Texas 77539 
The molecular genetic associations 
between populations of sand seatrout 
( Cynoscion arenarius) and silver seat- 
rout (C. nothus) have not been specifi- 
cally examined on a large scale with 
DNA methods despite the close ties 
between the respective fisheries for 
the two species. In particular, the pos- 
sibility of contemporary hybridization 
or historical admixture between these 
species remains to be explored by 
using a large panel of unlinked DNA 
markers. Sand and silver seatrout are 
so morphologically similar that they 
are collectively known as white trout 
by fishermen (Ginsburg, 1931). Both 
species are abundant throughout the 
Gulf of Mexico (hereafter, GOM); the 
distribution range for sand seatrout 
extends into the Atlantic Ocean, north 
to Georgia, and the distribution range 
for silver trout extends to Massachu- 
setts (Hildebrand and Schroeder, 1928; 
Cordes and Graves, 2003). These seat- 
rout make up a modest proportion of 
bycatch in shrimp and other commer- 
cial trawl operations (Warren, 1981), 
although commercial landings have 
decreased dramatically in the last 30 
years (Fig. 1). Weinstein and Yerger 
(1976) completed perhaps the most 
comprehensive study of molecular evo- 
lution in the genus Cynoscion ; they 
assessed protein electrophoresis vari- 
ants in all four western North Atlantic 
species (C. arenai'ius, C. nothus, spot- 
ted seatrout [C. nebulosus ], and gray 
weakfish [C. regalis\). Although these 
methods provided some insight into 
the evolutionary relationships among 
the species, the data of Weinstein 
and Yerger (1976) were insufficient 
to answer direct questions about rates 
of contemporary and recent historical 
gene flow within and among Cynoscion 
species. Enzyme electrophoresis has 
since been superceded by DNA-based 
methods on a broad scale. Microsatel- 
lite markers are likely more sensitive 
for studies involving high rates of gene 
flow and low levels of population iden- 
tity (Wright and Bentzen, 1994). This 
is particularly true for marine fishes, 
whose populations are often charac- 
terized by enormous census sizes and 
higher rates of migration between 
subpopulations than freshwater and 
terrestrial organisms (DeWoody and 
Avise, 2000). 
Previous morphological compari- 
sons of sand and silver seatrout have 
resulted in a suite of distinct charac- 
teristics that vary between species in 
larval (Ditty, 1989) and adult stages 
(Ginsburg, 1929, 1931; Gunter, 1945; 
Moshin, 1973; Chao, 2002). However, 
both display a similar streamlined 
and fusiform body shape, and the 
ranges of numerous commonly used 
morphometric and meristic measures 
